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HAND-BOOK 


OF 


PHYSIOLOGY. 


Digitized  by  the  Internet  Archive 

in  2010  with  funding  from 
Columbia  University  Libraries 


http://www.archive.org/details/handbookofphysioOOkirk 


KIRKES    HAND-BOOK    OF    FHY816WMY. 


HAND-BOOK 


PHYSIOLOGY. 


BY 

W.    MORRANT    BAKER;    F.R.C.S. 

s  to  st.  Bartholomew's  hospital  and  consulting  surgeon  to  the  evelina  hospital 

FOR   SICK    CHILDREN;    LECTURER    OX   PHYSIOLOGY   AT   ST.  BARTHOLOM  -     ITAL,    AND 

LATE   MEMBER    OF  THE   BOARD  OF    EXAMINERS   OF   THE   ROYAL  COLLEGE   OF 

SURGEONS    OF   ENGLAND. 

A>"T) 

VINCENT    DORMER    HARRIS,    M.D.  Loud., 

DEMONSTRATOR  OF  PHYSIOLOGY  AT   ST.   BARTHOLOMEW'S   HOSPITAL. 


(tMcbcntb    Orbit  ion. 


w :tz   nearly   f:tz    htitzezd   illtstzaz:: 


PHILADELPHIA  : 

P.    BLAKISTOX,    SOX    &    CO., 

1012,    WALNUT    STREET. 

l88+ 


VTli  l[[ 


^4 


PREFACE  TO  THE  ELEVENTH  EDITION 


Ix  the  preparation  of  the  present  edition  of  Kirkes' 
Physiology,  we  have  endeavoured  to  maintain  its  character 
as  a  guide  for  students,  especially  at  an  early  period  of 
their  career  ;  and,  while  incorporating  new  facts  and  observa- 
tions which  are  fairly  established,  we  have  as  far  as  possible 
omitted  the  controvertible  matters  which  should  only  find  a 
place  in  a  complete  treatise  or  in  a  work  of  reference. 

A  large  number  of  new  illustrations  have  been  added,  for 
many  of  which  we  are  indebted  to  the  com  I  :  Dr.  Klein, 

Professor  Michael  Foster,  Prole—  Schafer,  Dr.  Mahomed, 
Mr.  Gant,  and  Messrs.  McMillan,  who  have  been  so  good 
•  allow  various  figures  to  be  copied.  Our  thanks  are 
also  due  to  Mr.  Win.  Lapraik,  F.C.S.,  who  has  kindly  pre- 
pared a  table  of  the  absorption  spectra  oi  the  blood  and 
bile,  based  upon  his  own  observations ;  as  well  as  to  Mr.  S. 
K.  Alcock  for  several  careful  drawings  of  microscopical 
preparations,  and  for  reading  several  sheets  in  their  passage 
through  the  pr<  ss. 

Mr.  Danielsson,  of  the  firm  of  Lebon  &  Co.,  has  executed 
all  the  new  figures  to  our  entire  satisfaction :  and  for  the 
skill  and  labour  he  has  expended  upon  them  we  are  much 
indebted  to  him. 

We  are  desirous  also  of  acknowledging  the  help  we  have 
derived    from    the   following    works: — Klein's    Histoid 


vi  TREFACE    TO    THE    ELEVENTH    EDITION. 

M.  Foster's  Text  Book  of  Physiology ;  Pavy's  Food  and 
Dietetics  ;  Quain's  Anatomy,  Vol.  II.,  Ed.  ix. ;  Wickham 
Legg's  Bile,  Jaundice,  and  Bilious  Diseases  ;  Watney's 
Minute  Anatomy  of  the  Thymus;  Rosenthal's  Muscles  and 
Nerves ;  Cadiat's  Traite  D'Anatomie  Generale  ;  Ranvier's 
Traite  Technique  D 'Histologic ;  Landois'  Lehrbuch  der 
Physiologie  des  Menschen,  and  the  Journal  of  Physiology. 

W.  MOREANT  BAKER, 
V.  D.  HARRIS. 

Wimpole  Street, 
August,  1884. 


CONTENTS 


CHAPTER  I. 

PACK 

The  General  and  Distinctive  Characters  of  Living  Beings      i 


CHAPTER  II. 

Structural  Basis  of  the  Human  Body 5 

Cells ;h- 

Protoplasm 7 

Nucleus I1 

Intercellular  Substance    .                 20 

Fibres **• 

Tubules 21 


CHAPTER  III. 

Structure  of  the  Elementary  Tissues 21 

Epithelium 22 

Connective  Tissues 33 

Areolar  Tissue 37 

White  Fibrous  Tissue *&« 

Yellow  Elastic  Tissue 38 

Gelatinous 39 

Retiform  or  Adenoid 40 

Neuroglia 41 

Adipose 42 

Cartilage 46 

Bone 51 

Teeth 67 


CHAPTER  IV. 

The  Blood 78 

Quantity  of  Blood 79 

Coagulation  of  the  Blood 80 


viii  CONTEXTS. 


PAGE 

The  Blood— continued. 

Conditions  affecting  Coagulation 88 

The  Blood- Corpuscles 92 

Physical  and  Chemical  Characters  of  Bed  Blood-Cells       .        .     .  lb. 

The  White  Corpuscles,  or  Blood-Leucocytes 98 

Chemical  Composition  of  the  Blood 102 

The  [Serum 105 

Variations  in  Healthy  Blood  under  Different  Circumstances     .     .  107 
Variations  in  the  Composition  of  the  Blood  in  Different  Parts  of 

the  Body 108 

Gases  contained  in  the  Blood 109 

Blood- Crystals 112 

Development  of  the  Blood 119 

Uses  of  the  Blood 123 

Uses  of  the  various  Constituents  of  the  Blood     .  ih. 


CHAPTER  V. 

CIRCULATION  OF   THE   BLOOD 124 

The  Systemic,  Pulmonary,  and  Portal  Circulations    .        .        .    .  125 
The  Forces  concerned  in  the  Circulation  of  the  Blood     .        .        .127 

The  Heaet ' \l>. 

Structure  of  the  Valves  of  the  Heart 135 

The  Action  of  the  Heart 137 

Function  of  the  Valves  of  the  Heart 139 

Sounds  of  the  Heart    .                 145 

Impulse  of  the  Heart 147 

The  Cardiograph          .         .         .         .         .         .         .         .         .     .  148 

Frequency  and  Force  of  the  Heart's  Action 151 

Influence  of  the  Nervous  System  on  the  Action  of  the  Heart     .     .  154 

Effects  of  the  Heart's  Action 157 

The  Arteries.  Capillaries,  and  Veins 160 

Structure  of  the  Arteries 161 

Structure  of  Capillaries                164 

Structure  of  Veins 168 

Function  of  the  Arteries 171 

The  Pulse 177 

Sphygmograph 178 

Pressure  of  the  Blood  in  the  Arteries,  or  Arterial  Tension      .        .185 

The  Kymograph 186 

Influence  of  the  Nervous  System  on  the  Arteries    .        .        .        .  1 90 

Circulation  in  the  Capillaries 197 

Diapedesis  of  Blood-Corpuscles 198 


CONTENTS, 


IX 


Circulation  in  tin:  Varus 201 

Blood-pres8aie  in  the  veins 202 

:ity  of  the  Circulation 203 

ity  of  the  Blood  in  the  Arteries 204 

.,    Capillaries 206 

r                   „           ••     Veins #. 

Velocity  of  the  Circulation  as  a  whole ib. 

Peculiarities  of  the  Circulation  in  Different  Parts        .  208 

Circulation  in  the  Brain *&« 

Circulation  in  the  Erectile  Structures 210 

Agents  concerned  in  the  Circulation 211 

Discovery  of  the  Circulation 212 

Proofs  of  the  Circulation  of  the  Blood ib. 


CHAPTER  VI. 


Respiration 

Position  and  Structure  of  the  Lungs  . 
Structure  of  the  Trachea  and  Bronchial  Tubes 
Structure  of  Lobules  of  the  Lungs 
Mechanism  of  Respiration        .... 
Respiratory  Movements       .... 

Respiratory  Rhythm 

Respiratory  Sounds     ..... 
Respiratory  Movements  of  Glottis  . 
Quantity  of  Air  respired      .... 
Vital  or  Respiratory  Capacity 
Force  exerted  in  Respiration 
Circulation  of  Blood  in  the  Respiratory  Organs 
Changes  of  the  Air  in  Respiration 
Changes  produced  in  the  Blood  by  Respiration 
Mechanism  of  various  Respiratory  Actions . 
Influence  of  the  Nervous  System  in  Respiration 
Effects  of  Vitiated  Air — Ventilation   . 
Effect  of  Respiration  on  the  Circulation  . 
Apncea — Dyspnoea — Asphyxia     . 


214 

215 

218 

221 

227 

ib. 


233 

ib. 

234 

ib. 

235 
236 
ib. 
238 

244 

247 

249 

252 

253 

25S 


CHAPTER  VII. 

Foods 262 

Classification  of  Foods 264 

Foods  containing  chiefly  Nitrogenous  Bodies      ....  265 

„  „  „        Carbohydrate  Bodies      .        .        .     .  267 


CONTEXTS. 


Foods — continued. 

Foods  containing  chiefly  Fatty  Bodies 
Substances  supplying  the  Salts 
liquid  Foods 

Effects  of  Cooking       .... 

Effects  of  an  Insufficient  Diet . 

Starvation 

Effects  of  Improper  Food 

Effects  of  too  much  Food    . 

Diet  Scale 


268 
ib. 
ib. 

ib. 

269 
270 
272 
273 
275 


CHAPTER  VIII. 

Digestion 276 

Passage  of  Food  through  the  Alimentary  Canal         .        .  277 

Mastication 278 

Insalivation 279 

The  Salivary  Glands  and  the  Saliva ib. 

Structure  of  the  Salivary  Glands ib. 

The  Saliva 283 

Influence  of  the  Xervous  System  on  the  Secretion  of  Saliva  .        .  285 

The  Pharynx 291 

The  Tonsils ib. 

The  CEsophagus  or  Gullet 292 

Swallowing  or  Deglutition      ....                 ...  294 

Digestion  of  Food  in  the  Stomach 296 

Structure  of  the  Stomach 297 

Gastric  Glands 299 

The  Gastric  Juice 303 

Functions  of  the  Gastric  Juice 305 

Movements  of  the  Stomach 308 

Vomiting 310 

Influence  of  the  Nervous  System  on  Gastric  Digestion    .        .        .312 

Digestion  of  the  Stomach  after  Death 313 


Digestion  in  the  Intestines 315 

Structure  of  the  Small  Intestine ib. 

Yalvulae  Conniventes 317 

Glands  of  the  Small  Intestine ib. 

The  Villi 321 

Structure  of  the  Large  Intestine 325 

The  Pancreas  and  its  Secretion 328 


CONTENTS.  xi 

DlGBSTION    IN   THE    lXTKSTINKS— nmtiniiol. 

Structure  of  the  Liver 332 

Functions  of  the  Liver 338 

The  Bile ib. 

The  Li ver  as  a  Blood-elaborating  Organ 347 

Glycogenic  Function  of  the  Liver      .......  348 

Summary  of  the  Changes  which  take  place  in  the  Food  during  its 

Passage  through  the  Small  Intestine 352 

Succus  Entericus    .        .        . 351 

Summary  of  the  Process  of  Digestion  in  the  Large  Intestine    .     .  355 

Defecation 357 

1 1   -os  contained  in  the  Stomach  and  Intestines          .        .        .     .  358 

Movements  of  the  Intestines 359 

Influence  of  the  Nervous  System  on  Intestinal  Digestion          .     .  360 


CHAPTER  IX. 

Absorption 361 

The  Lacteal  and  Lymphatic  Vessels  and  Glands        .         ...  ib. 

Lymphatic  Glands 368 

Properties  of  Lymph  and  Chyle 373 

Absorption  by  the  Lacteal  Vessels 375 

Absorption  by  the  Lymphatic  Vessels 376 

Absorption  by  Blood-vessels 377 


CHAPTER  X. 

Animal  Heat 382 

Variations  in  Bodily  Temperature ib. 

Sources  of  Heat 384 

Loss  of  Heat 387 

Production  of  Heat 390 

Inhibitory  Heat-centre 391 


CHAPTER  XI. 

Secretion 393 

Secreting  Membranes 394 

Serous  Membranes ib. 

Mucous  Membranes 396 


xii  CONTENTS. 

PACE 

Secretion — eont  in  ued. 

Secreting  Glands 39s 

Process  of  Secretion 401 

Circumstances  influencing  Secretion          ....  403 

Mammary  Glands  and  their  Secretion          .        .        .    .  405 

Chemical  Composition  of  Milk 409 


CHAPTER  XII. 

The  Skin  and  its  Functions 410 

Structure  of  the  Skin .         .         .  ib. 

Sudoriparous  Glands            416 

Sebaceous  Glands 417 

Structure  of  Hair 418 

Structure  of  Nails 421 

Functions  of  the  Skin 422 


CHAPTER  XIII. 

The  Kidneys  and  Urine 422 

Structure  of  the  Kidneys  .  428 

Structure  of  the  Ureter  and  Urinary  Bladder        ....  436 

The  Urine  437 

The  Secretion  of  Urine 450 

Micturition 460 


CHAPTER  XIY. 


The  Vascular  Glands 

Structure  and  Functions  of  the  Spleen 

.      ib. 

i) 

Thymus  .         .         .         .         . 

.     .    466 

JJ                  ;>                 » 

Thyroid        .... 

.    468 

>»               ••               n 

Supra-renal  capsules 

.     .     469 

>'                   s?                   »» 

Pituitary  Body 

•     472 

5J                          •■> 

Pineal  Gland 

.     .      ib. 

Functions  of  the  Vascular  Glands  in  general 

.      ib. 

CHAPTER  XV. 

Causes  and  Phenomena  of  Motion  474 

Ciliary  Motion ib. 

Amoeboid  Motion 475 


CONTENTS.  xiii 


iw.r. 

Causes  and  Phenomena  of  Motion — continued. 

Muscular  Motion 47° 

Plain  or  Onstriped  Muscle ib. 

Btriated  Muscle 47s 

Development  of  Muscle 4^3 

I'hvsiology  of  Muscle  at  rest 4<v>4 

„             ,,                 in  activity 4^8 

Rigor  Mortis             5°4 

Actions  of  the  Voluntary  Muscles 5°7 

„             „        Involuntary  Muscles 511 

Sources  of  Muscular  Action 512 

Electrical  Currents  in  Nerves 5r3 


CHAPTER  XVI. 

The  Voice  and  Speech 518 

Mode  of  Production  of  the  Human  Voice ib. 

The  Larynx 520 

Application  of  the  Voice  in  Singing  and  Speaking          .        .         .526 
Speech 530 


CHAPTER  XVII. 

Nutrition  :  The    Income   and  Expenditure   of   the  Human 

Body 533 

Nitrogenous  Equilibrium  and  Formation  of  Fat        .         .         .     .     538 


CHAPTER  XVIII. 

The  Nervous  System 540 

Elementary  Structures  of  the  Nervous  System            .        .         .     .  ib. 

Structure  of  Nerve-Fibres 541 

Terminations  of  Nerve-Fibres             547 

Structure  of  Nerve-Centres 550 

Functions  of  Nerve  Fibres 552 

Classification  of  Nerve-Fibres 554 

Laws  of  Conduction  in  Nerve-Fibres 555 

Functions  of  Nerve-Centres 558 

Laws  of  Reflex  Actions 560 

Secondary  or  Acquired  Reflex  Actions 562 


xiv  CONTENTS. 

PAGE 

Cerebrospinal  Nervous  System 564 

The  Spiual  Cord  and  its  Nerves 565 

The  White  Matter  of  the  Spinal  Cord 567 

The  Grey  Matter  of  the  Spinal  Cord 568 

Nerves  of  the  Spinal  Cord 569 

Functions  of  the  Spinal  Cord 573 

The  Medulla  Oblongata 583 

Its  Structure ib. 

Distribution  of  the  Fibres  of  the  Medulla  Oblongata      .        .        .  584 

Functions  of  the  Medulla  Oblongata 587 

Structure   and  Physiology  of    the   Pons  Varolii.   Crura 
Cerebri.    Corpora    Quadrigemina.    Corpora    Geniculata. 

Optic  Thai.ami.  and  Corpora  Striata 590 

Pons  Varolii ib. 

Crura  Cerebri  ...         ........  ib. 

Corpora  Quadrigemina 592 

Corpora  Striata  and  Optic  Thalami 593 

The  Cerebellum 595 

Functions  of  the  Cerebellum 596 

The  Cerebrum 600 

Convolutions  of  the  Cerebrum 601 

Structure  of  the  Cerebrum 604 

Chemical  Composition  of  the  Grey  and  White  Matter   .        .        .  606 

Functions  of  the  Cerebrum .  608 

Effects  of  the  Piemoval  of  the  Cerebrum 609 

Localisation  of  Functions 610 

Experimental  Localisation  of  Functions 613 

Sleep 617 

Physiology  of  the  Cranial  Nerves n>. 

Physiology  of  the  Third  Cranial  Nerve 620 

..               ,,       Fourth  Cranial  Nerve 621 

.,               „       Fifth  or  Trigeminal  Nerve 622 

,,               „      Sixth  Nerve 627 

„               ,,       Facial  Nerve 628 

.,               ..       Glosso- Pharyngeal  Nerve 630 

,,               .,       Pneumogastric  Nerve 631 

.,               .,       Spinal  Accessory  Nerve 635 

.,       Hypoglossal  Nerve ib. 

Physiology  of  the  Spinal  Nerves 636 

Physiology  of  the  Sympathetic  Nerve ib. 

Functions  of  the  Sympathetic  Nervous  System      ....  640 


I  ONTENTS.  xv 


CHAPTER  XIX. 


PAGE 

The  Senses      .        .               646 

Commit.  9          ions ib. 

satians 647 

The  Sense  of  Touch 651 

The  Sense  of  Taste 65S 

The  Tongue  and  its  Papillae 659 

The  Sense  of  Smell 666 

The  Sense  of  Hearing 671 

Anatomy  of  the  Organ  of  Hearing 672 

Phy         _       f  Hearing 6-9 

Functions  of  the  External  Ear                 .         .         .         .         .    .  ib. 

Functions  of  the  Middle  Ear  :   the  Tympanum.  Ossicula.  and 

Fenestras 6S0 

Functions  of  the  Labyrinth 6S- 

Sensibility  of  the  Auditory  Nerve 


The  Sense  of  sight 

The  Eyelids  and  Lachrymal  Apparatus 

The  Structure  of  the  Eye-ball .... 

Optical  Appara:    - 

Accommodation  of  the  Eye       .... 

Defects  in  the  Apparatus 

Spherical  Aberration 

Chromatic  Aberration 

The  Blind  Spot 

Visual  Purple 

Col        Sensations 

Eeciprocal  Action  of  different  parts  of  the  Ketina 

Movements  of  the  Eye 

Simultaneous  Action  of  the  two'Ev  -  . 


691 

692 

ib. 

699 

"03 
7cS 
710 
7ii 

713 
716 

7-3 

n 

729 


CHAPTER  XX. 

Generation  and  Development   ....  -,«=; 

/  ju 

Generative  Organs  of  the  Female ^ 

Enimpregnated  Ovum -,q 

the  Ovum -  V, 

Menstruation »., 

Corpus  Luteum *.- 


xvi  CONTEXTS. 

PAGE 

Generation  and  Development — continued. 

Impregnation  of  the  Ovum 75° 

Male  Sexual  Functions *&« 

Structure  of  the  Testicle *& 

Spermatozoa 752 

The  Semen 75^ 

Development 757 

Changes  of  the  Ovum  up  to  the  Formation  of  the  Blastoderm        .  ib. 

Segmentation  of  the  Ovum 759 

Fundamental  Layer-  of  the  Blastoderm  :   Epiblast  ;    Mesbblast  ; 

Hypoblast 760 

First  Rudiments  of  the  Embryo  and  its  Chief  Organs        .         .     .  761 

Fcetal  Membrane- 767 

The  Umbilical  Vesicle 769 

The  Amnion  and  Allantois ib. 

The  Chorion 771 

Changes  of  the  Mucous  Membrane  of  the  Uterus  and  Formation 

of  the  Placenta 773 

Development  of  Organs 778 

Development  of  the  Vertebral  Column  and  Cranium       .         .         .  ib. 

..     Face  and  Visceral  Arches 782 

.,     Extremities 784 

..                 ..      Vascular  System 785 

Circulation  of  Blood  in  the  Foetus 796 

Development  of  the  Nervous  System 798 

..      Organs  of  Sense 802 

Alimentary  Canal        .         .         .         .         .     .  806 

Respiratory  Apparatus    .....  810 

Wolffian    Bodies.    Urinary    Apparatus,    and 

Sexual  Organs 810 


CHAPTER  XXI. 

On  the  Relation  of  Life  to  other  Forces       ....    819 


APPENDIX. 
The  Chemical  Basis  of  the  Human  Body 844 


CONTENTS.  xvii 


ArPENDIX  B: 

PAGE 

Anatomical  Weights  and  Measures 86 1 

Measures  of  Weight ib. 

n       ..  Length ib. 

Sizes  of  various  Histological  Elements  and  Tissues     .         .         .     .  862 

Specific  Gravity  of  various  Fluids  and  Tissues        ....  863 
Table  showing  the  per-centage  composition  of  various  Articles  of 

Food ib. 

Classification  of  the  Animal  Kingdom 864 

ib. 


French   Measurements  of  Length,  Capacity,  and   Weight 

rendered  into  English  Equivalents xviii 

Table  for  converting  Degrees  of  the  Fahrenheit  Thermo- 
meter Scale  into  Degrees  Centigrade        ....     ib. 


INDEX S67 


TO  BINDER. 
The  Coloured  Plate  to  face  p.  115. 


XY111 


*Table  for  converting  Degrees 
of  tie  FAHRENHEIT  Ther- 
mometer Scale  into  Degrees 

CENTIGRADE. 

Fahrenheit.  Cbktigbadb. 

5ooD   260° 

401    205 

392    200 

383    195 

374    190 

356    180 

347    175 

338    170 

329    165 

320    160 

311    155 

302    150 

284    140 

275    135 

266    130 

248    120 

239    115 

230    110 

212    100 

203    95 

194    90 

176    80 

167    75 

140    60 

122    50 

113    45 

105    40-54 

104    40 

100    37-8 

98-5   36-9 

95    35 

86    30 

77        25 

68    20 

50   10 

41    5 

32  Zero  0 

23    -  5 

14    -10 

+  5    -15 

-  4    -20 

-13    —25 

-22    -30 

-40     -40 

-76    -60 

1  degree  Fahr.  =  •54°  C. 

18  '..  „   =  1°C. 

3-6   ..  ..   =  2°  C. 

4-5   ..  ..   =  2-5°  C. 

5-4   ••  -,   =  3°  C. 

*  Modified  from  Fownes'  Chemistry. 


MEASUREMENTS. 

FRENCH   INTO    ENGLISH. 


1  metre 
10  decimetres 
100  centimetres 
.000  millimetres 


LENGTH. 

\ 


=  39*37  English 

inches 
(or  1  yard  and  3^  in.) 


i  decimetre 
10  centimetres 
100  millimetres 


=  3'937  inches 
(or  nearly  4  inches) 


1  centimetre 
10  millimetres 

1  milli  metre 


=  '3937  or  about 
(nearly  §  inch.) 

=  nearly  i  inch. 


CAPACITY. 

1. 000  cubic  decimetres     ~| 

,  .  ..    ,,  J-  =  1  cubic  metre 

1. 000.000  cubic  centimetres    J 

1  cubic  decimetre        \ 

or  (  =  1  litre 

!  •  ,.    u         (      Cmi  fluid  oz.. 

1.000  cubic  centimetres     J     ormther  less  than 

an  English  quart) 


WEIGHT. 


1  gramme 
10  decigrammes 
100  centigrammes 
1. 000  millierammes 


=  i5"432349  grs. 
(or  nearly  15*) 


i  decigramme 
10  centigrammes 
100  milligrammes 


=  rather  more 
than  ii  grain 


1  centigramme 
10  decigrammes 


-  =  rather  more 

than  530  grain 


millier  i^nme 


=  rather  more 
tnan  sb  grain 


Measure  of  1  decimetre,  or  10  centimetres,  or  100  millimetres. 


Cranium. 

7  Cervical  Vertebrae. 

Clavicle. 
Scapula. 

12  Dorsal  Vertebrae. 
Humerus. 

5  Lumbar  Vertebrae. 


Hiuni. 

Ulnar. 

Eadius. 

Pelvis. 


Bones  of  the  Carpus. 

Bones  of  the  Meta- 
carpus. 

Phalanges  of  Fingers. 
Femur. 


-     Patella. 


Tibia. 
Fibula. 


Bones  of  the  Tarsus. 
Bones  of  the  Meta- 
tarsus. 
Phalanges  of  Toes. 


THE    SKELETON   (after  Holdex). 


Highest 
point  of 
Crest  of  the 
Ilium . 


Anterior  Su- 
perior Spine 
of  the  Hium. 


Symphysis  Pubis. 


DIAGRAM    OF    THORACIC    AND    ABDOMINAL    REGIONS. 


A .  Aortic  Valve. 
M.  Mitral  Valve. 


P.  Pulmonary  Valve. 
T.  Tricuspid  Valve. 


HANDBOOK    OF    PHYSIOLOGY. 


CHAPTER    I. 

TEE    GENERAL    AXD    DISTINCTIVE    CHARACTERS    OF 
LIVING    BEINGS. 

Hitman  Physiology  is  the  science  which  treats  of  the  life  of 
man — of  the  way  in  which  he  lives,  and  moves,  and  has  his  being. 
It  teaches  how  man  is  begotten  and  born  ;  how  he  attains  ma- 
turity ;  and  how  he  dies. 

Having,  then,  man  as  the  object  of  its  study,  it  is  unnecessary 
to  speak  here  of  the  laws  of  life  in  general,  and  the  means  by 
which  they  are  carried  out,  further  than  is  requisite  for  the  more 
clear  understanding  of  those  of  the  life  of  man  in  particular. 
Yet  it  would  be  impossible  to  understand  rightly  the  working  of  a 
complex  machine  without  some  knowledge  of  its  motive  power  in 
the  simplest  form ;  and  it  may  be  well  to  see  first  what  are  the  so- 
called  essential*  of  life — those,  namely,  which  are  manifested  by 
all  living  beings  alike,  bv  the  lowest  vegetable  and  the  highest 

©  ©  "  v  ©  © 

animal — before  proceeding  to  the  consideration  of  the  structure 
and  endowments  of  the  organs  and  tissue  belonging  to  man. 

The  essentials  of  life  are  these, — Birth,  Growth  and  Development, 
Decline  and  Death. 

The  term  birth,  when  employed  in  this  general  sense  of  one  of 
the  conditions  essential  to  life,  without  reference  to  any  particular 
kind  of  living  being,  may  be  taken  to  mean,  separation  from  a 
parent,  with  a  greater  or  less  power  of  independent  life. 

Taken  thus,  the   term,   although  not   defining  any  particular 

ge  in  development,  serves  well  enough  for  the  expression  of  the 
fact,  to  which  no  exception  has  yet  been  proved  to  exist,  that  the 
capacity  for  life  in  all  living  beings  is  obtained  by  inheritance. 

B 


2  GROWTH.  [chap.  I. 

Growth,  or  inherent  power  of  increasing  in  size,  .although 
essential  to  our  idea  of  life,  is  not  confined  to  living  beings.  A 
crystal  of  common  salt,  or  of  any  other  similar  substance,  if  placed 
under  appropriate  conditions  for  obtaining  fresh  material,  will 
grow  in  a  fashion  as  definitely  characteristic  and  as  easily  to  be 
foretold  as  that  of  a  living  creature.  It  is,  therefore,  necessary  to 
explain  the  distinctions  which  exist  in  this  respect  between  living 
and  lifeless  structures  ;  for  the  manner  of  growth  in  the  two  cases 
is  widely  different. 

Differences  between  Living  and  Lifeless  Growth. — 
(i.)  The  growth  of  a  crystal,  to  use  the  same  example  as  before, 
takes  place  merely  by  additions  to  its  outside :  the  new  matter 
is  laid  on  particle  by  particle,  and  layer  by  layer,  and,  when 
once  laid  on,  it  remains  unchanged.  The  growth  is  here  said  to 
be  superficial.  In  a  living  structure,  on  the  other  hand,  as,  for 
example,  a  brain  or  a  muscle,  where  growth  occurs,  it  is  by  addi- 
tion of  new  matter,  not  to  the  surface  only,  but  throughout  even- 
part  of  the  mass ;  the  growth  is  not  superficial  but  interstitial, 

(2.)  All  living  structures  are  subject  to  constant  decay ;  and 
life  consists  not,  as  once  supposed,  in  the  power  of  preventing  this 
never-ceasing  decay,  but  rather  in  making  up  for  the  loss  atten- 
dant on  it  by  never-ceasing  repair.  Thus,  a  man's  body  is  not 
composed  of  exactly  the  same  particles  day  after  day,  although  to 
all  intents  he  remains  the  same  individual.  Almost  every  part  is 
changed  by  degrees ;  but  the  change  is  so  gradual,  and  the  re- 
newal of  that  which  is  lost  so  exact,  that  no  difference  may  be 
noticed,  except  at  long  intervals  of  time.  A  lifeless  structure,  as 
a  crystal,  is  subject  to  no  such  laws  ;  neither  decay  nor  repair 
is  a  necessary  condition  of  its  existence.  That  which  is  true  of 
structures  which  never  had  to  do  with  life  is  true  also  with  re- 
spect to  those  which,  though  they  are  formed  by  living  parts,  are 
not  themselves  alive.  Thus,  an  oyster-shell  is  formed  by  the 
living  animal  which  it  encloses,  but  it  is  as  lifeless  as  any  other 
mass  of  inorganic  matter ;  and  in  accordance  with  this  circumstance 
its  growth  takes  place,  not  interstitially,  but  layer  by  layer,  and 
it  is  not  subject  to  the  constant  decay  and  reconstruction  which 
belong  to  the  living.  The  hair  and  nails  are  examples  of  the 
same  fact. 

(3.)  In  connection  with  the  growth  of  lifeless  masses  there  is  no 


ohap.  I.]  DEVELOPMENT.  3 

alteration  in  the  chemical  constitution  of  the  material  which  is 
taken  up  and  added  to  the  previously  existing  mass.  For  example, 
when  a  crystal  of  common  salt  grows  on  being  placed  in  a  fluid 

which  contains  the  same  material,  the  properties  of  the  salt  are 
not  changed  by  being  taken  out  of  the  liquid  by  the  crystal  and 
added  to  its  surface  in  a  solid  form.  But  the  case  is  essentially 
different  in  living  beings,  both  animal  and  vegetable.  A  plant, 
like  a  crystal,  can  only  grow  when  fresh  material  is  presented  to 
it ;  and  this  is  absorbed  by  its  leaves  and  roots ;  and  animals,  for 
the  same  purpose  of  getting  new  matter  for  growth  and  nutrition, 
take  food  into  their  stomachs.  But  in  both  these  cases  the 
materials  are  much  altered  before  they  are  finally  assimilated  by 
the  structures  they  are  destined  to  nourish. 

(4.)  The  growth  of  all  living  things  has  a  definite  limit,  and  the 
law  which  governs  this  limitation  of  increase  in  size  is  so  invariable 
that  we  should  be  as  much  astonished  to  find  an  individual  plant 
or  animal  without  limit  as  to  growth  as  without  limit  to  life. 

Development  is  as  constant  an  accompaniment  of  life  as 
growth.  The  term  is  used  to  indicate  that  change  to  which, 
before  maturity,  all  living  parts  are  constantly  subject,  and  by 
which  they  are  made  more  and  more  capable  of  performing  their 
several  functions.  For  example,  a  full-grown  man  is  not  merely  a 
magnified  child  ;  his  tissues  and  organs  have  not  only  grown,  or 
increased  in  size,  they  have  also  developed,  or  become  better  in 
quality. 

No  very  accurate  limit  can  be  drawn  between  the  end  of  de- 
velopment and  the  beginning  of  decline ;  and  the  two  processes 
may  be  often  seen  together  in  the  same  individual.  But  after  a 
time  all  parts  alike  share  in  the  tendency  to  degeneration,  and 
this  is  at  length  succeeded  by  death. 

Differences  between  Plants  and  Animals. — It  has  been 
already  said  that  the  essential  features  of  life  are  the  same  in  all 
living  things  ;  in  other  words,  in  the  members  of  both  the  animal 
and  vegetable  kingdoms.  It  may  be  well  to  notice  briefly  the 
distinctions  which  exist  between  the  members  of  these  two  king- 
doms. It  may  seem,  indeed,  a  strange  notion  that  it  is  possible 
to  confound  vegetables  with  animals,  but  it  is  true  with  respect 
to  the  lowest  of  them,  in  which  but  little  is  manifested  beyond 
the  essentials  of  life,  which  are  the  same  in  both. 

b  2 


4  ANIMALS    CONTRASTED  [chap.  i. 

(i.)  Perhaps  the  most  essential  distinction  is  the  presence  or 
absence  of  power  to  live  upon  inorganic  material.  By  means  of 
their  green  colouring  matter,  chlorophyl — a  substance  almost 
exclusively  confined  to  the  vegetable  kingdom,  plants  are  capable 
of  decomposing  the  carbonic  acid,  ammonia,  and  water,  which  they 
absorb  by  their  leaves  and  roots,  and  thus  utilizing  them  as  food. 
The  result  of  this  chemical  action,  which  occurs  only  under  the 
influence  of  light,  is,  so  far  as  the  carbonic  acid  is  concerned,  the 
fixation  of  carbon  in  the  plant  structures  and  the  exhalation  of 
oxygen.  Animals  are  incapable  of  thus  using  inorganic  matter, 
and  never  exhale  oxygen  as  a  product  of  decomposition. 

The  power  of  living  upon  organic  as  well  as  inorganic  matter 
is  less  decisive  of  an  animal  nature  ;  inasmuch  as  fungi  and  some 
other  plants  derive  their  nourishment  in  part  from  the  former 
source. 

(2.)  There  is,  commonly,  a  marked  difference  in  general  chemical 
composition  between  vegetables  and  animals,  even  in  their  lowest 
forms  ;  for  while  the  former  consist  mainly  of  cellulose,  a  substance 
closely  allied  to  starch  and  containing  carbon,  hydrogen,  and 
oxygen  only,  the  latter  are  composed  in  great  part  of  the  three 
elements  just  named,  together  with  a  fourth,  nitrogen ;  the  chief 
proximate  principles  formed  from  these  being  identical,  or  nearly 
so,  with  albumen.  It  must  not  be  supposed,  however,  that  either 
of  these  typical  compounds  alone,  with  its  allies,  is  confined  to  one 
kingdom  of  nature.  Nitrogenous  compounds  are  freely  produced 
in  vegetable  structures,  although  they  form  a  very  much  smaller 
proportion  of  the  whole  organism  than  cellulose  or  starch.  And 
while  the  presence  of  the  latter  in  animals  is  much  more  rare  than 
is  that  of  the  former  in  vegetables,  there  are  many  animals  in 
which  traces  of  it  may  be  discovered,  and  some,  the  Ascidians,  in 
which  it  is  found  in  considerable  quantity. 

(3.)  Inherent  power  of  movement  is  a  quality  which  we  so 
commonly  consider  an  essential  indication  of  animal  nature,  that 
it  is  difficult  at  first  to  conceive  it  existing  in  any  other.  The 
capability  of  simple  motion  is  now  known,  however,  to  exist  in  so 
many  vegetable  forms,  that  it  can  no  longer  be  held  as  an  essential 
distinction  between  them  and  animals,  and  ceases  to  be  a  mark  by 
which  the  one  can  be  distinguished  from  the  other.  Thus  the 
zoospores  of  many  of  the  Cryptogamia  exhibit  ciliary  or  amoeboid 


chap,  ii.]  WITH    VEGETABLES.  5 

movements  (p.  9)  of  a  like  kind  to  those  seen  in  animalcules* \ 
and  even  among  the  higher  orders  of  plants,  many,  e.g.,  Dioncea 
Mttscipula  (Venus'a  fly-trap),  and  Mimosa  Sensitwa  (Sensitive 
plant),  exhibit  such  motion,  either  at  regular  times,  or  on  the 
application  of  external  irritation,  as  might  lead  one  were  this 
tact  taken  by  itself,  to  regard  them  as  sentient  beings.  InhnvnT 
power  of  movement,  then,  although  especially  characteristic  of 
animal  nature,  is.  when  taken  by  itself,  no  proof  of  it. 

(4.)  The  presence  of  a  digestive  canal  is  a  very  general  mark  by 
which  an  animal  can  be  distinguished  from  a  vegetable.  But  the 
lowest  animals  are  surrounded  by  material  that  they  can  take  as 
food,  as  a  plant  is  surrounded  by  an  atmosphere  that  it  can  use  in 
like  manner.  And  every  part  of  their  body  being  adapted  to 
absorb  and  digest,  they  have  no  need  of  a  special  receptacle  for 
nutrient  matter,  and  accordingly  have  no  digestive  canal.  This 
distinction  then  is  not  a  cardinal  one. 

It  would  be  tedious  as  well  as  unnecessary  to  enumerate  the 
chief  distinctions  between  the  more  highly  developed  animals  and 
vegetables.  They  are  sufficiently  apparent.  It  is  necessary  to 
compare,  side  by  side,  the  lowest  members  of  the  two  kingdoms, 
in  order  to  understand  rightly  how  faint  are  the  boundaries 
between  them. 


CHAPTEE    II. 

STRUCTURAL    BASIS    OF    THE    HITMAN    BODY. 

By  dissection,  the  human  body  can  be  proved  to  consist  of 
various  dissimilar  parts,  bones,  muscles,  brain,  heart,  lungs,  in- 
testines, &c.,  while,  on  more  minute  examination,  these  are  found 
to  be  composed  of  different  tissues,  such  as  the  connective,  epithe- 
lial, nervous,  muscular,  and  the  like. 

Cells. — Embryology  teaches  us  that  all  this  complex  organisa- 
tion has  been  developed  from  a  microscopic  body  about  y^  in.  in 
diameter  (ovum),  which  consists  of  a  spherical  mass  of  jelly-like 
matter    enclosing    a    smaller    spherical    body    (germinal    vesicle). 


6  STRUCTURAL    BASIS    OF    THE    HUMAN    BODY.     [chap.  ii. 

Further,  each  individual  tissue  can  be  shown  largely  to  consist 
of  bodies  essentially  similar  to  an  ovum,  though  often  differing 
from  it  very  widely  in  external  form.  They  are  termed  cells  :  and 
it  must  be  at  once  evident  that  a  correct  knowledge  of  the  nature 
and  activities  of  the  cell  forms  the  very  foundation  of  physiology. 

Cells  are,  in  fact,  physiological  no  less  than  histological  units. 

The  prime  importance  of  the  cell  as  an  element  of  structure 
was  first  established  by  the  researches  of  Schleiden,  and  his  con- 
clusions, drawn  from  the  study  of  vegetable  histology,  were  at  once 
extended  by  Schwann  to  the  animal  kingdom.  The  earlier 
observers  defined  a  cell  as  a  more  or  less  spherical  body 
limited  by  a  membrane,  and  containing  a  smaller  body  termed 
a  nucleus,  which  in  its  turn  encloses  one  or  more  nucleoli.  Such 
a  definition  applied  admirably  to  most  vegetable  cells,  but  the  more 
extended  investigation  of  animal  tissues  soon  showed  that  in  many 
cases  no  limiting  membrane  or  cell-wall  could  be  demonstrated. 

The  presence  or  absence  of  a  cell-wall,  therefore,  was  now  re- 
garded as  quite  a  secondary  matter,  while  at  the  same  time  the 
cell-substance  came  gradually  to  be  recognised  as  of  primary  im- 
portance. Many  of  the  lower  forms  of  animal  life,  e.g.,  the 
Rhizopoda,  were  found  to  consist  almost  entirely  of  matter  very 
similar  in  appearance  and  chemical  composition  to  the  cell-sub- 
stance of  higher  forms  :  and  this  from  its  chemical  resemblance  to 
flesh  was  termed  Sarcode  by  Dujardin.  When  recognised  in 
vegetable  cells  it  was  called  Protojilasm  by  Mulder,  while  Remak 
applied  the  same  name  to  the  substance  of  animal  cells.  As  the 
presumed  formative  matter  in  animal  tissues  it  was  termed 
Blastema,  and  in  the  belief  that,  wherever  found,  it  alone  of  all 
substances  has  to  do  with  generation  and  nutrition,  Beale  has 
named  it  Germinal  matter  or  Bioplasm.  Of  these  terms  the  one 
most  in  vogue  at  the  present  day  is  Protoplasm,  and  inasmuch  as 
all  life,  both  in  the  animal  and  vegetable  kingdoms,  is  associated 
with  protoplasm,  we  are  justified  in  describing  it,  with  Huxley, 
as  the  "physical  basis  of  life." 

A  cell  may  nowT  be  defined  as  a  nucleated  mass  of  protoplasm,* 
of  microscopic  size,  which  possesses  sufficient  individuality  to  have 
a  life-history  of  its  own.     Each  cell   goes  through  the  same  cycle 


*  In  the  human  body  the  cells  range  from  the  red  blood-cell  (g^in.)  to 
the  ganglion-cell  (3^  in.). 


ohap.  ii.]  PROTOPLASM.  7 

of  changes  as  the  whole  organism,  though  doubtless  in  a  much 
shorter  time.  Beginning  with  its  origin  from  Borne  pre-existing 
cell,  it  grows,  produces  other  colls,  and  finally  dies.  It  is  true  that 
several  Lower  forms  of  life  consist  of  non-nucleated  protoplasm,  but 
the  above  definition  holds  good  for  all  the  higher  plants  and  animals. 

Hence  a  summary  of  the  manifestations  of  cell-life  is  really  an 
account  of  the  vital  activities  of  protoplasm. 

Protoplasm. — Physical  characters. —  Physically,  protoplasm  is 
viscid,  varying  in  consistency  from  semi-fluid  to  strongly  coherent. 
Chemical  characters. — Chemically,  living  protoplasm  is  an  ex- 
tremely unstable  albuminoid  substance,  insoluble  in  water.  It 
is  neutral  or  weakly  alkaline  in  reaction.  It  undergoes  heat 
stiffening  or  coagulation  at  about  130°^.  (54'5°C.),  and  hence  no 
organism  can  live  when  its  own  temperature  is  raised  beyond 
this  point,  though,  of  course,  many  can  exist  for  a  time  in  a 
much  hotter  atmosphere,  since  they  possess  the  means  of  regu- 
lating their  own  temperature.  Besides  the  coagulation  produced 
by  heat,  protoplasm  is  coagulated  by  all  the  reagents  which 
produce  this  change  in  albumen.  If  not-living  protoplasm  be 
subjected  to  chemical  analysis  it  is  found  to  be  made  up  of  nume- 
rous bodies*  besides  albumen,  e.g.,  of  glycogen,  lecithin,  salts  and. 
water,  so  that  if  living  protoplasm  be,  as  some  believe,  an  inde- 
pendent chemical  body,  when  it  no  longer  possesses  life,  it  under- 
goes a  disintegration  which  is  accompanied  by  the  appearance  of 
these  new  chemical  substances.  When  it  is  examined  under  the 
microscope  two  varieties  of  protoplasm  are  recognised — the  hyaline, 
and  the  granular.  Both  are  alike  transparent,  but  the  former  is 
perfectly  homogeneous,  while  the  latter  (the  more  common  variety) 
contains  small  granules  or  molecules  of  various  sizes  and  shapes. 
Globules  of  watery  fluid  are  also  sometimes  found  in  protoplasm  ; 
they  look  like  clear  spaces  in  it,  and  are  hence  called  vacuoles. 

Vital  or  Physiological  characters. — These  may  be  conveniently 
treated  under  the  three  heads  of — I.  Motion ;  II.  Nutrition  ; 
and  III.  Reproduction. 

I.  Motion. — It  is  probable  that  the  protoplasm  of  all  cells  is 
capable  at  some  time  of  exhibiting  movement;  at  any  rate  this 
phenomenon,  which  not  long  ago  was  regarded  as  quite  a  curiosity, 

*  For  an  account  of  which,  reference  should  be  made  to  the  Appendix. 


STRUCTURAL    BASIS    OF    THE    HUMAN    BODY.     [chap.  ii. 


has  been  recently  observed  in  cells  of  many  different  kinds.  It 
may  be  readily  studied  in  the  Amoebic,  in  the  colourless  blood- 
cells  of  all  vertebrata,  in  the  branched  cornea-cells  of  the  frog,  in 
the  hairs  of  the  stinging-nettle  and  Tradescantia,  and  the  cells  of 
Yallisneria  and  Chara. 

These  motions  may  be  divided  into  two  classes — (a)  Fluent 
and  (b)  Ciliary. 

Another  variety — the  molecular  or  vibratory — has  also  been  classed  by 
some  observers  as  vital,  but  it  seems  exceedingly  probable  that  it  is  nothing 
more  than  the  well-known  "  Brownian  "  molecular  movement,  a  purely 
mechanical  phenomenon  which  may  be  observed  in  any  minute  particles 
e.g.,  of  gamboge,  suspended  in  a  fluid  of  suitable  density,  such  as  water. 

Such  particles  are  seen  to  oscillate  rapidly  to  and  fro,  and  not  to  progress 
in  any  definite  direction. 

(a.)  Fluent. — This  movement  of  protoplasm  is  rendered  percep- 
tible (i)  by  the  motion  of  the  granules,  which  are  nearly  always 
imbedded  in  it,  and  (2)  by  changes  in  the  outline  of  its  mass. 

If  part  of  a  hair  of  Tradescantia  (fig.  1 )  be  viewed  under  a  high 
magnifying  power,  streams   of  protoplasm    containing  crowds   of 

granules  hurrying  along, 
like  the  foot  passengers  in 
a  busy  street,  are  seen 
flowing  steadily  in  definite 
directions,  some  coursing 
round  the  film  which  lines 
the  interior  of  the  cell-wall, 
and  others  flowing  towards 
or  away  from  the  irregular 
mass  in  the  centre  of  the 
cell-cavity.  Many  of  these 
streams  of  protoplasm  run 
together  into  larger  ones, 
and  are  lost  in  the  central 
mass,  and  thus  ceaseless  variations  of  form  are  produced. 

In  the  Amoeba,  a  minute  animal  consisting  of  a  shapeless  and 
structureless  mass  of  sarcode,  an  irregular  mass  of  protoplasm  is 
gradually  thrust  out  from  the  main  body  and  retracted  :  a  second 
mass  is  then  protruded  in  another  direction,  and  gradually  the 
whole  protoplasmic  substance  is,  as  it  were,  drawn  into  it.  The 
Amoeba  thus  comes  to  occupy  a  new  position,  and  when  this  is 


Fig.  1. — Cell  of  Tradescantia  drawn  at  successive 
intervals  of  two  minutes.  The  cell-contents 
consist  of  a  central  mass  connected  by  many 
irregular  processes  to  a  peripheral  film  :  the 
whole  forms  a  vacuolated  mass  of  protoplasm, 
which  is  continually  changing  its  shape. 
(Schofield.) 


obap.ii.]  PEOTOPLASMIC    KOTION.  9 

repeated  several  times  we  have  locomotion  in  a  definite  direction, 
together  with  a  continual  change  <»t'  form.  These  movements 
when  observed  in  other  cells,  such  as  the  colourless  blood-cor- 
puscles of  higher  animals  (fig.  2)  are  hence  termed  amoeboid. 

Colourless  blood-corpuscles  were  first  observed  to  migrate,  /.<"..  past 
through  the  walls  of  the  blood-vessels  (p.  198).  by  Waller,  whose  observations 
were  confirmed  and  extended  to  connective  tissue  corpuscles  by  the  re- 
searches 1  if  Recklinghausen,  ( !ohnheim,  and  others,  and  thus  the  phenomenon 
of  migration  has  been  proved  to  play  an  important  part  in  many  normal, 
and  pathological  processes,  especially  in  thai  of  inflammation. 

This  amoeboid  movement  enables  many  of  the  lower  animals  to 
capture  their  prey,  which  they  accomplish  by  simply  flowing  round 
and  enclosing  it. 

The  remarkable  motions  of  pigment-granules  observed  in  the 

branched  pigment-cells  of  the  frog's  skin  by  Lister  are  probably 


Fig.  2. — Human  colourless  blood-eorpiiscle,  showing-  its  successive  changes  of  outline  within 
ten  minutes  when  kept  moist  on  a  warm  stage.     (Schoneld.) 

due  to  amoeboid  movement.  These  granules  are  seen  at  one  time 
distributed  uniformly  through  the  body  and  branched  processes 
of  the  cell,  while  under  the  action  of  various  stimuli  (e.f/.,  light 
and  electricity)  they  collect  in  the  central  mass,  leaving  the 
branches  quite  colourless. 

(b.)  Ciliary  action  must  be  regarded  as  only  a  special  variety  of 
the  general  motion  with  which  all  protoplasm  is  endowed. 

The  grounds  for  this  view  are  the  following  :  In  the  case  of  the 
Infusoria,  which  move  by  the  vibration  of  cilia  (microscopic  hair- 
like processes  projecting  from  the  surface  of  their  bodies)  it  has 
been  proved  that  these  are  simply  processes  of  their  protoplasm 
protruding  through  pores  of  the  investing  membrane,  like  the  oars 
of  a  galley,  or  the  head  and  legs  of  a  tortoise  from  its  shell : 
certain  reagents  cause  them  to  be  partially  retracted.  Moreover, 
in  some  cases  cilia  have  been  observed  to  develop  from,  and  in 
others  to  be  transformed  into,  amoeboid  processes. 

The  movements  of  protoplasm  can  be  very  largely  modified  or 
even  suspended  by  external  conditions,  of  which  the  following  are 
the  most  important. 


10        STRUCTURAL    BASIS    OF    THE    HUMAN    BODY.      [chap  rr. 

i.  Changes  of  temperature. — Moderate  heat  aets  as  a  stimulant : 
this  is  readily  observed  in  the  activity  of  the  movements  of  a 
human  colourless  blood-corpuscle  when  placed  under  conditions 
in  which  its  normal  temperature  and  moisture  are  preserved. 
Extremes  of  heat  and  cold  stop  the  motions  entirely. 

2.  Mechanical  stimuli. — When  gently  squeezed  between  a  cover 
and  object  glass  under  proper  conditions,  a  colourless  blood-cor- 
puscle is  stimulated  to  active  amoeboid  movement. 

3.  Nerve  influence. — By  stimulation  of  the  nerves  of  the  frog's 
cornea,  contraction  of  certain  of  its  branched  cells  has  been 
produced. 

4.  Chemical  stimuli. — Water  generally  stops  amoeboid  move- 
ment, and  by  imbibition  causes  great  swelling  and  finally  bursting 
of  the  cells. 

In  some  cases,  however,  (myxomycetes)  protoplasm  can  be 
almost  entirely  dried  up,  and  is  yet  capable  of  renewing  its  motions 
when  again  moistened. 

Dilute  salt-solution  and  many  dilute  acids  and  alkalies,  stimu- 
late the  movements  temporarily. 

Ciliary  movement  is  suspended  in  an  atmosphere  of  hydrogen 
or  carbonic  acid,  and  resumed  on  the  admission  of  air  or  oxygen. 

5.  Electrical. — Weak  currents  stimulate  the  movement,  while 
strong  currents  cause  the  corpuscles  to  assume  a  spherical  form 
and  to  become  motionless. 

II.  Nutrition. — The  nutrition  of  cells  will  be  more  appro- 
priately described  in  the  chapters  on  Secretion  and  Nutrition. 

Before  describing  the  Reproduction  of  cells  it  will  be  necessary 
to  consider  their  structure  more  at  length. 

Minute  Structure  of  Cells. — (a.)  Cell-ivall. — We  have  seen 
(p.  6)  that  the  presence  of  a  limiting-membrane  is  no  essential 
part  of  the  definition  of  a  cell. 

In  nearly  all  cells  the  outer  layer  of  the  protoplasm  attains  a 
firmer  consistency  than  the  deeper  portions :  the  individuality  of 
the  cell  becoming  more  and  more  clearly  marked  as  this  cortical 
layer  becomes  more  and  more  differentiated  from  the  deeper 
portions  of  cell-substance.  Side  by  side  with  this  physical,  there 
is  a  gradual  chemical  differentiation,  till  at  length,  as  in  the  case 
of  the  fat-cells,  we  have  a  definite  limiting  membrane  differing 
chemically  as  well  as  physically  from  the  cell-contents,  and  re- 


CHAP.  II.]  MINUTE    STRUCTURE    OF    CELLS.  U 

maining  as  a  Bhrivelled-up  bladder  when  they  have  beeD  removed. 
Such  a  membrane  is  transparent  and  structureless,  flexible,  and 
permeable  to  fluids. 

The  cell-substance  can,  therefore,  still  be  nourished  by  imbibi- 
tion through  the  cell-wall.  In  many  cases  (especially  in  fat)  a 
membrane  of  some  toughness  is  absolutely  necessary  to  give  to 
the  tissue  the  requisite  consistency.  When  these  membranes 
attain  a  certain  degree  of  thickness  and  independence  they  are 
termed  capsules  :  as  examples,  we  may  cite  the  capsules  of 
cartilage-cells,  and  the  thick,  tough  envelope  of  the  ovum  termed 
the  "  primitive  chorion." 

(b.)  Cell  content*. — In  accordance  with  their  respective  ages, 
positions,  and  functions,  the  contents  of  cells  are  very  varied. 

The  original  protoplasmic  substance  may  undergo  many  trans- 
formations; thus,  in  fat  cells  we  may  have  oil,  or  fatty  crystals, 
occupying  nearly  the  whole  cell-cavity  :  in  pigment  cells  we  find 
granules  of  pigment  ;  in  the  various  gland  cells  the  elements  of 
their  secretions.  Moreover,  the  original  protoplasmic  contents  of 
the  cell  may  undergo  a  gradual  chemical  change  with  advancing 
_■■  ;  thus  the  protoplasmic  cell-substance  of  the  deeper  layers  of 
the  epidermis  becomes  gradually  converted  into  keratin  as  the 
cell  approaches  the  surface.  So,  too,  the  original  protoplasm  of 
the  embryonic  blood-cells  is  replaced  by  the  haemoglobin  of  the 
mature  coloured  blood-corpuscle. 

The  minute  structure  of  cells  has  lately  been  made  the  subject 
of  careful  investigation,  and  what  was  once  regarded  as  homo- 
geneous protoplasm  with  a  few  scattered  granules,  has  been  stated 
to  be  an  exceedingly  complex  structure.  In  colourless  blood- 
corpuscles,  epithelial  cells,  connective  tissue  corpuscles,  nerve- 
cells,  and  many  other  varieties  of  cells,  an  intracellular  network 
of  very  fine  fibrils,  the  meshes  of  which  are  occupied  by  a  hyaline 
interstitial  substance,  has  been  demonstrated  (Heitzmann's  net- 
work) (fig.  3).  At  the  nodes,  where  the  fibrils  cross,  are  little 
Bwellings,  and  these  are  the  objects  described  as  granules  by  the 
older  observers  :  but  in  some  cells,  e.</.,  colourless  blood-corpuscles, 
there  are  real  granules,  which  appear  to  be  quite  free  and  un- 
connected with  the  intra-cellular  network. 

(c.)  yucleus. — Xuclei(fig.  3)  were  first  pointed  out  in  the  year  1833, 
by  Robert  Brown,  who  observed  them  in  vegetable  cells.     They  are 


12         STRUCTURAL    BASIS    OF    THE    HUMAN    I30DY.      [chap.  ii. 

either  small  transparent  vesicular  bodies  containing  one  or  more 
smaller  particles  (nucleoli),  or  they  are  semi-solid  masses  of  proto- 
plasm always  in  the  resting  condition  bounded  by  a  well-defined 
envelope.  In  their  relation  to  the  life  of  the  cell  they  are  certainly 
hardly  second  in  importance  to  the  protoplasm  itself,  and  thus 
Beale    is    fully    justified    in    comprising-    both    under    the    term 


Fig".  3 — (a).  Colourless  blood-corpuscle  showing  intra-cellular  network  of  Heitzma.nu,  and  two 
nuclei  with  intra-nuclear  network.    (Klein  and  Noble  Smith.) 
(b.)  Colon red  blood-corpuscle  of  newt  showing  intra-cellular  network  of  fibrils  (Heitzmann). 
Also  oval  nucleus  composed  of  limiting-  membrane  and  fine  intra-nuclear  network 
of  fibrils,     x  800.     (Klein  and  Noble  Smith.) 

"germinal  matter."  They  exhibit  their  vitality  by  initiating  the 
process  of  division  of  the  cell  into  two  or  more  cells  (fission)  by  first 
themselves  dividing.  Distinct  observations  have  been  made  show- 
ing that  spontaneous  changes  of  form  may  occur  in  nuclei  as  also 
in  nucleoli. 

Histologists  have  long  recognised  nuclei  by  two  important 
characters  : — 

(1.)  Their  power  of  resisting  the  action  of  various  acids  and 
alkalies,  particularly  acetic  acid,  by  which  their  outline  is  more 
clearly  defined,  and  they  are  rendered  more  easily  visible.  This 
indicates  some  chemical  difference  between  the  protoplasm  of  the 
cell  and  nuclei,  as  the  former  is  destroyed  by  these  reagents. 

(2.)  Their  quality  of  staining  in  solutions  of  carmine,  hema- 
toxylin, &c.  Nuclei  are  most  commonly  oval  or  round,  and  do 
not  generally  conform  to  the  diverse  shapes  of  the  cells  ;  they  are 
altogether  less  variable  elements  than  cells,  even  in  regard  to  size, 
of  which  fact  one  may  see  a  good  example  in  the  uniformity  of  the 
nuclei  in  cells  so  multiform  as  those  of  epithelium.  But  some- 
times nuclei  appear  to  occupy  the  whole  of  the  cell,  as  is  the 
case  in  the  lymph  corpuscles  of  lymphatic  glands  and  in  some 
small  nerve  cells. 


obap.il]  REPRODUCTION    OF    CELl  13 

Their  position   in  the   cell  is   very  variable.     In    many  cells, 
dally  where  rth  is  1  ring,  two  or  more  1. 

are  present. 

The  nuclei  <>f  many  ells   ha  shown  to  contain  a 

\-nuclear  network  in  every  oilar  to  th  I  ribed 

■bore  as  intra-eellnlar  (fig.  3),  the  tut  of  which  are  occu- 

pied by  Bemi-fluid  protopla>m. 

III.  Reproduction. — The  life  of  individual  cells  is  probably 
very  short  in  comparison  with  that  of  the  organism  they  com] 

and  their  constant  decay  and  death  necessitate  constant  repro- 
duction. The  mode  in  which  this  takes  place  has  1'  _  d  the 
subject  of  great  controversy. 

In  the  case  of  plants,  all  of  whoe     tisE      a    ire  either  cellular  or 

composed  of  cells  which  are  modified  or  have  1  in  various 

.  the  theory  that  all  new  cells  are  derived  from  pre-existimr 

was  early  advanced  and  very  generally  accepted.     But  in  the 

3  of  animal  tise  -  Schwann  and  others  maintained  a  theory  of 
spontaneous  or  free  cell  formation. 

According-  to  this  view  a  minute  corpuscle  (the  future  nucle- 
olus) springs  np  spontaneously  in  a  structureless  substance 
(blastema)  very  much  as  a  crystal  is  formed  in  a  solution.  This 
nucleolus  attracts  the  suiTOundin-  molecules  of  matter  to  form  the 
nucleus,  and  by  a  repetition  of  the  process  the  substance  and  wall 
are  produced. 

This  theory,  once  almost  universally  current,  was  first  disputed 
and  finally  overthrown  by  Remak  and  Virchow,  whose  researches 
established  the  truth  expressed  in  the  words  -•  Omnis  cellula  e 
cellula/' 

It  will  be  seen  that  this  view  is  in  strict  accordance  with  the 

truth  established  much  earlier  in  Vegetable  Histology  that  every 

cell    is   descended   from   some   pre-existimr    (mother-)   cell.     This 

derivation  of  cells  from   cells  takes  place  by  (1)  gemmation^  or 

■a  or  division. 

(1.)  Gemmation. — This  method  has  not  been  observed  in  the 
human  body  or  the  higher  animals,  and  therefore  requires  but  a 
og  notice.  It  consists  ssentially  in  the  budding  off  and 
.rating  of  a  portion  of  the  parent  cell. 

(2.)  Fission  or  Din  ision. — As  examples  of  reproduction  by  fission, 
we  may  select  the  ovum,  the  blood  cell,  and  cartilage  cells. 


H 


STRUCTUllAL    BASIS    OF    THE    HUMAN    BODY.     [chap.  11. 


In  the  frog's  ovum  (in  which  the  process  can  he  most  readily 
observed)  after  fertilization  lias  taken  place,  there  is  first  some 
amoeboid  movement,  the  oscillation  gradually  increasing  until  a 
permanent  dimple  a])] tears,  which  gradually  extends  into  a  furrow 
running  completely  round  the  spherical  ovum,  and  deepening 
until  the  entire  yelk-mass  is  divided  into  two  hemispheres  of 
protoplasm  each  containing  a  nucleus  (fig.  4,   b).     This  process 


Fig.  4. — Diagram  of  an  ovum  (a)  undergoing  segmentation.  In  [b)  it  has  divided  into 
•  two  ;  in  (c)  into  f our ;  and  in  (d)  the  process  has  ended  in  the  production  of  the  so- 
called  "  mulberry  mass."    (Frey.) 

being  repeated  by  the  formation  of  a  second  furrow  at  right 
angles  to  the  first,  we  have  four  cells  produced  (c) :  this  subdivision 
is  carried  on  till  the  ovum  has  been  divided  by  segmentation  into 
a  mass  of  cells  (mulberry-mass)  (d)  out  of  which  the  embryo  is 
developed. 

Segmentation  is  the  first  step  in  the  development  of  most 
animals,  and  doubtless  takes  place  in  man. 

Multiplication  by  fission  has  been  observed  in  the  colourless 
blood-cells  of  many  animals.     In  some  cases  (fig.  5),  the  process 


®  ®  6    @ 


Fig.  5. — Blood-corpuscle  from  a  young  deer  embryo,  multiplying  by  fission.    (Frey.) 


has  been  seen  to  commence  with  the  nucleolus  which  divides 
within  the  nucleus.  The  nucleus  then  elongates,  and  soon  a  well- 
marked  constriction  occurs,  rendering  it  hour-glass  shaped,  till 
finally  it  is  separated  into  two  parts,  which  gradually  recede  from 
each  other  :  the  same  process  is  repeated  in  the  cell-substance, 
and  at  length  we  have  two  cells  produced  which  by  rapid  growth 
soon  attain  the  size  of  the  parent  cell  {direct  division).  In  some 
cases  there  is  a  primary  fission  into  three  instead  of  the  usual  two 
cells. 


Ml  IP.    II. J 


CELL    DIVISION. 


15 


In  cartilage  (fig.  6),  a  prod  mtially  similar  occurs,  with  the 

exception  that  (as  in  the   ovum)  the   cells   produced    by  fission 
remain  in  the  original  capsule,  and  in  their  turn  undergo  division, 


Fig.  6. — Diagram  of  a  cartilagi  cell  undergoing  fission  within  its  capsule.  The  process  of 
division  is  represented  as  commencing  in  the  nucleolus,  extending  to  the  nucleus,  and 
at  length  involving  the  body  of  the  cell.     (Frey.) 

s<»  that  a  large  number  of  cells  are  sometimes  observed  within  a 
common  envelope.  This  process  of  fission  within  a  capsule  has 
been  by  some  described  as  a  separate  method,  under  the  title 
"  endogenous  fission,"  but  there  seems  to  be  no  sufficient  reason 
for  drawing  such  a  distinction. 

It  is  important  to  observe  that  fission  is  often  accomplished 
with  great  rapidity,  the  whole  process  occupying  but  a  few 
minutes,  hence  the  comparative  rarity  with  which  cells  are  seen 
in  the  act  of  dividing. 

Indirect  cell  division. — In  certain  and  numerous  cases  the  divi- 
sion of  cells  does  not  take  place  by  the  simple  constriction  of  their 
nuclei  and  surrounding  protoplasm  into  two  parts  as  above  described 
(direct  division),  but  is  preceded  by  complicated  changes  in  their 
nuclei  (karyokinesis).  These  changes  consist  in  a  gradual  re- 
arrangement of  the  intranuclear  network  of  each  nucleus,  until  tw<  > 
nuclei  are  formed  similar  in  all  respects  to  the  original  one.  The 
nucleus  in  a  resting  condition,  i.e.,  before  any  changes  preceding 
division  occur,  consists  of  a  very  close  meshwork  of  fibrils, 
which  stain  deeply  in  carmine,  imbedded  in  protoplasm,  which 
does  not  possess  this  property,  the  whole  nucleus  being 
contained  in  an  envelope.  The  first  change  consists  of  a  slight 
enlargement,  the  disappearance  of  the  envelope,  and  the  increased 
definition  and  thickness  of  the  nuclear  fibrils,  which  are  also  more 
separated  than  they  were  and  stain  better.    This  is  the  stage  of  con- 


1 6        STRUCTURAL    BASIS    OF    THE    HUMAN    BODY.     [chap.  h. 

volution  (fig.  7,  b,  c).  The  next  step  in  the  process  is  the  arrange- 
ment of  the  fibrils  into  some  definite  figure  by  an  alternate  looping 
in  and  out  around  a  central  space,  by  which  means  the  rosette  or 
wreath  stage  (fig.  7,  d)  is  reached.      The  loops  of  the  rosette  next 


Fig.  7. — Koryokinesis.  a,  ordinary  nucleus  of  a  columnar  epithelial  cell ;  b,  c,  the  same 
nucleus  in  the  stage  of  convolution  ;  d,  the  wreath  or  rosette  form  ;  e,  the  aster  or  single 
star  ;  f,  a  nuclear  spindle  from  the  Descemet's  endothelium  of  the  frog's  cornea  ;  a,  h, 
1,  diaster;  k,  two  daughter  nuclei.     (Klein.) 

become  divided  at  the  periphery,  and  their  central  points  become 
more  angular,  so  that  the  fibrils,  divided  into  portions  of  about 
equal  length,  are,  as  it  were,  doubled  at  an  acute  angle,  and  radiate 
Y-shaped  from  the  centre,  forming  a  star  (aster)  or  wheel  (fig.  7,  e), 
or  perhaps  from  two  centres,  in  which  case  a  double  star  (diaster) 
results  (fig.  7,  G,  h,  and  1).  After  remaining  almost  unchanged 
for  some  time,  the  V-shaped  fibres  being  first  re-arranged  in  the 
centre,  side  by  side  (angle  outwards),  tend  to  separate  into  two 
bundles,  which  gradually  assume  position  at  either  pole  From 
these  groups  of  fibrils  the  two  nuclei  of  the  new  cells  are  formed 
(daughter  nuclei)  (fig.  7,  k),  and  the  changes  they  pass  through 
before  reaching  the  resting  condition  are  exactly  those  through 
which  the  original  nucleus  (mother  nucleus)  has  gone,  but  in  a 
reverse  order,  viz.,  the  star,  the  rosette,  and  the  convolution.  During 
or  shortly  after  the  formation  of  the  daughter  nuclei  the  cell  itself 
becomes  constricted,  and  then  divides  in  a  line  about  midway 
between  them. 

Functions  of  Cells. — The  functions  of  cells  are  almost  infinitely 
varied  and  make  up  nearly  the  whole  of  Physiology.     They  will 


chap,  ii.]  DECAY    AND    DEATH    OP    CEL1  17 

l>e  more  appropriately  considered  in  the  chapters  treating  of  the 
nis  and  systems  of  organs  which  the  cells  compot 
Decay  and  Death  of  Cells.     There  aretwo  chief  ways  in  which 
the  comparatively  brief  existence  of  cells  is  brought   to  an  end. 
Mechanical  abrasion,  (2)  Chemical  transformation. 

1.  The  various  epithelia  furnish  abundant  examples  of  mecha- 
nical abrasion.  As  it  approaches  the  free  surface  the  cell  be© 
more  and  more  flattened  and  scaly  in  form  and  more  horny  in 
consistence,  rill  at  length  it  is  simply  rubbed  off.  Hence  we  find 
epithelial  cells  in  the  mucus  of  the  mouth,  intestine,  and  genito- 
urinary tract. 

2.  In  the  case  of  chemical  transformation  the  cell-contents 
undergo  a  degeneration  which,  though  it  may  be  pathological,  is 
very  often  a  normal  process. 

Thus  we  have  (a.)  fatty  metamorphosis  producing  oil-globules  in 
the  secretion  of  milk,  fatty  degeneration  of  the  muscular  fibres  of 
the  uterus  after  the  birth  of  the  foetus,  and  of  the  cells  of  the 
<  rraanan  follicle  giving  rise  to  the  ;'  corpus luteuni."  (See  chapter 
On  ( feneration.) 

( 1». )  Pigmentary  degeneration  from  deposit  of  pigment,  as  in  the 
epithelium  of  the  air-vesicles  of  the  lungs. 

(c.)  Calcareous  degeneration  which  is  common  in  the  cells  of 
many  cartilages. 

Having  thus  reviewed  the  life-history  of  cells  in  general,  we  may 
now  discuss  the  leading  varieties  of  form  which  they  present. 

In  passing,  it  may  be  well  to  point  out  the  main  distinctions  It-ticeen 
(ini'iuii  ninl  vegetable  cells. 

It  has  been  already  mentioned  that  in  animal  cells  an  envelope  or  cell- 
wall  is  by  no  means  always  present.  In  adult  vegetable  cells,  on  the  other 
hand,  a  well-defined  cellulose  wall  is  highly  characteristic  ;  this,  it  should 
be  observed,  is  non-nitrogenous,  and  thus  differs  chemically  as  well  as 
structurally  from  the  contained  ma-. 

Moreover,  in  vegetable  cells  (fig.  8,  b).  the  protoplastic  contents  of  the 
cell  fall  into  two  subdivisions  :  (1)  a  continuous  film  which  lines  the  interior 
of  the  cellulose  wall  ;  and  (2)  a  reticulate  mass  containing  the  nucleus  and 
occupying  the  cell-cavity  ;  \t<  interstices  are  filled  with  nuid.  In  young 
vegetable  cells  such  a  distinction  does  not  exist  ;  a  finely  granular  proto- 
plasm occupies  the  whole  cell-cavity  (fig.  8,  A). 

Another  striking  difference  is  the  frequent  presence  of  a  large  quantity 
of  intercellular  substance  in  animal  tissues,  while  in  vegetables  it  is  com 
paratively  rare,  the  requisite  consistency  being  given  to  their  tissues  by  the 

c 


!8        STRUCTURAL    BASIS    OF    THE    HUMAN    BODY.     [chap.  ir. 


tough  cellulose  walls,  often  thickened  by  deposits  of  lignin.  In  animal 
cells  this  end  is  attained  by  the  deposition  of  lime-salts  in  a  matrix  of  inter- 
cellular substance,  as  in  the  process  of  ossification. 


Fig.  8. — (a).   Young  vegetable  cells,  showing  cell-eavity  entirely  filled  with  granular  proto- 
plasm enclosing  a  large  oval  nucleus,  with  one  or  more  nucleoli. 
(b.)  Older  cells  from  same  plant,  showing  distinct  cellulose-wall  and  vacuolation  of 
protoplasm. 

Forms  of  Cells. — Starting  with  the  spherical  or  spheroidal  (fig. 
9,  a)  as  the  typical  form  assumed  by  a  free  cell,  we  find  this 
altered  to  a  polyhedral  shape  when  the  pressure  on  the  cells  in  all 
directions  is  nearly  the  same  (fig.  9,  b). 

Of  this,  the  primitive  segmentation-cells  may  afford  an  example. 


Fig.  9. — Various  forms  of  cells,    a.  Spheroidal,  showing  nucleus  and  nucleolus,     b.  Poly- 
hedral,   c.  Discoidal  (blood-cells),    d.  Scaly  or  squamous  (epithelial  cells,. 


The  discoid  shape  is  seen  in  blood-cells  (fig.  9,  c),  and  the  scale- 
like form  in  superficial  epithelial  cells  (fig.  9,  d).  Some  cells  have 
a  jagged  outline  (prickle-cells)  (fig.  13). 

Cylindrical,  conical,  or  prismatic  cells  occur  in  the  deeper  layers 
of  laminated  epithelium,  and  the  simple  cylindrical  epithelium  of 
the  intestine  and  many  gland  ducts.  Such  cells  may  taper  off  at 
one  or  both  ends  into  fine  processes,  in  the  former  case  being- 
caudate,  in  the  latter  fusiform  (fig.  10).  They  may  be  greatly 
elongated  so  as  to  become  fibres.  Ciliated  cells  (fig.  10,  d)  must 
be  noticed  as  a  distinct  variety  :  they  possess,  but  only  on  their 
free  surfaces,  hair-like  processes  (cilia).     These  vary  immensely  in 


CHAP.   II.  | 


CLASSIFICATION    OF    CELLS. 


19 


si/.c,  and  may  even  exceed  in  length  the  cell  itself.  Finally  we 
have  the  branched  or  stellate  cells,  of  which  the  large  nerve-cells 
of  the  spinal  cord,  and  the  connective  tissue  corpuscle  are  typical 


Fig.  10.—  Various  forms  of  cetts.    a.  Cylindrical  or  columnar.    l>.  Caudate,    c.  Fusiform. 
d.  Ciliated  (from  trachea),    e.  Branched,  stellate. 


examples  (fig.  10,  e).  In  these  cells  the  primitive  branches  by 
secondary  branching  may  give  rise  to  an  intricate  network  of 
processes. 


Classification  of  Cells. — Cells  may  be  classified  in  many 
ways.     According  to  : — 

(a.)  Form :  They  may  be  classified  into  spheroidal  or  polyhedral, 
discoidal,  flat  or  scaly,  cylindrical,  caudate,  fusiform,  ciliated  and 
stellate. 

(b.)  Situation  : — we  may  divide  them  into  blood  cells,  gland 
cells,  connective  tissue  cells,  &c. 

(c.)  Contents : — fat  and  pigment  cells  and  the  like. 

(d.)  Function  : — secreting,  protective,  contractile,  &c. 

(e.)  Origin: — hypoblastic,  mesoblastic,  and epiblastic  cells.  (See 
chapter  on  Generation.) 

It  remains  only  to  consider  the  various  ways  in  which  cells 
are  connected  together  to  form  tissues,  and  the  transforma- 
tions by  which  intercellular  substance,  fibres  and  tubules  are 
produced. 

Modes  of  connection. — Cells  are  connected  : — 

(1)  By  a  cementing  intercellular  substance.  This  is  probably 
always  present  as   a  transparent,   colourless,  viscid,    albuminous 

c  2 


20        STRUCTURAL    BASIS    OF    THE    HUMAN    BODY.     [chap.  ii. 

substance,  even  between  the  closely  apposed  cells  of  cylindrical 
epithelium,  while  in  the  case  of  cartilage  it  forms  the  main  bulk 
of  the  tissue,  and  the  cells  only  appear  as  imbedded  in,  not  as 
cemented  by,  the  intercellular  substance. 

This  intercellular  substance  may  be  either  homogeneous  or 
fibrillated. 

In  many  cases  {e.g.  the  cornea)  it  can  be  shown  to  contain  a 
number  of  irregular  branched  cavities,  which  communicate  with 
each  other,  and  in  which  the  branched  cells  lie  :  through  these 
branching  spaces  nutritive  fluids  can  find  their  way  into  the  very 
remotest  parts  of  a  non-vascular  tissue. 

As  a  special  variety  of  intercellular  substance  must  be  mentioned 
the  basement  membrane  (membrana  propria)  which  is  found  at 
the  base  of  the  epithelial  cells  in  most  mucous  membranes,  and 
especially  as  an  investing  tunic  of  gland  follicles  which  determines 
their  shape,  and  which  may  persist  as  a  hyaline  saccule  after  the 
gland-cells  have  all  been  discharged. 

(2)  By  anastomosis  of  their  processes. 

This  is  the  usual  way  in  which  stellate  cells,  e.g.  of  the  cornea, 
are  united  :  the  individuality  of  each  cell  is  thus  to  a  great  extent 
lost  by  its  connection  with  its  neighbours  to  form  a  reticulum  : 
as  an  example  of  a  network  so  produced,  we  may  cite  the  stroma 
of  lymphatic  glands. 

Sometimes  the  branched  processes  breaking  up  into  a  maze 
of  minute  fibrils,  adjoining  cells  are  connected  by  an  inter- 
mediate reticulum :  this  is  the  case  in  the  nerve-cells  of  the  spinal 
cord. 

Besides  the  Cell,  which  may  be  termed  the  primary  tissue- 
element,  there  are  materials  which  may  be  termed  secondary  or 
derived  tissue-elements.  Such  are  Intercellular  substance,  Fibres 
and  Tubules. 

Intercellular  substance  is  probably  in  all  cases  directly  derived 
from  the  cells  themselves.  In  some  cases  (e.g.  cartilage),  by  the 
use  of  re-agents  the  cementing  intercellular  substance  is,  as  it 
were,  analysed  into  various  masses,  each  arranged  in  concentric 
ayers  around  a  cell  or  group  of  cells,  from  which  it  was  probal  try 
derived  (fig.  6). 

Fibres. — In  the  case  of  the  crystalline  lens,   and  of  muscle  both 


.  n.J  TTJBUU  21 

and  noi  imply  a 

cell  :   in  * 

by  a  multifile;  -  the  nuclei. 

The  various  fibres  and  fibrflls  anective 

gradual   transfonuatioii    of  an    originally   homogeneous   inter- 
cellular   subsl  Fil  pea    thus    formed    may  undergo    g 
chemical  ;t^  well  as  physical  transformation  :  this  is  notably  the 
.  It  i  i  yellow  el.  -  ie,  in  which  the  sharply  defined  el 
3se8s     _  _  vat  power  of  resistance  t"         _ 
strik:    _         rith    the    homog  tter  from  which  they  are 
derive"  1. 

f  which  wen        _    ally  supposed  i  ructure- 

membrane,  have  now  been  proved  to  be  composed  of  flat,  thin 

Iges,       3      I  lapillariea 

With  these  simple  materials  the  various  parts  of  the  body  are 

built  up;  the  more  elementary  tissues  bein_.  -  *  speak,  first 
compounded  of  them  :  while  these  again  are  variously  mixed  and 
interwoven  to  form  ni'-re  intricate  combinations. 

Thus  are  constructed  epithelium  and  its  modifications,  connec- 
tive tissue,  fat.  cartihiL'e,  bone,  the  fibres  of  muscle  and  nerve.  Arc. : 
and  these,  again,  with  the  more  simple  structures  before  men- 
tioned, are  usee  -  materials  wherewith  to  fomi  arteries,  veins, 
and  lympha:  3,  e  reting  md  vascular  glands,  lungs,  heart,  liver, 
and  other  pans  of  the  body. 


CHAPTEB    III. 

STRUCTURE   OF   THE  ELEMENTARY  TISSUES. 

In  this  chapter  the  leading  characters  and  chief  modifica: 
of  two  great  groups  of  tissues — the  Epithelial  and  Connective — 
•will    be    briefly    described;    while    the    Xerv.»us    and    Muscular, 
together  with  several  other  m  _  -       ialized  .  will 

be   appropriately  considered    in    the    chapters    treating    of  their 
physioL  _ 


22  STRUCTURE    OF    ELEMENTARY    TISSUES.        [chap.  hi. 

Epithelium. 

Epithelium  is  composed  of  cells  of  various  shapes  held  together 
by  a  small  quantity  of  cementing  intercellular  substance. 

Epithelium  clothes  the  whole  exterior  surface  of  the  bod}', 
forming  the  epidermis  with  its  appendages — nails  and  hairs; 
becoming  continuous  at  the  chief  orifices  of  the  body — nose, 
mouth,  anus,  and  urethra — with  the  epithelium  which  lines  the 
whole  length  of  the  alimentary  and  genito-urinary  tracts,  together 
with  the  ducts  of  their  various  glands.  Epithelium  also  lines  the 
cavities  of  the  brain,  and  the  central  canal  of  the  spinal  cord,  the 
serous  and  synovial  membranes,  and  the  interior  of  all  blood- 
vessels and  lymphatics. 

The  cells  composing  it  may  be  arranged  in  either  one  or  more 
layers,  and  thus  it  may  be  sub-divided  into  (a)  Simple  and  (b)  Stra- 
tified or  laminated  Epithelium.  A  simple  epithelium,  for  example, 
lines  the  whole  intestinal  mucous  membrane  from  the  stomach  to 
the  anus  :  the  epidermis  on  the  other  hand  is  laminated  throughout 
its  entire  extent. 

Epithelial  cells  possess  an  intracellular  and  an  intranuclear  net- 
work (p.  n).  They  are  held  together  by  a  clear,  albuminous, 
cement  substance.  The  viscid  semi-fluid  consistency  both  of  cells 
and  intercellular  substance  permits  such  changes  of  shape  and 
arrangement  in  the  individual  cells  as  are  necessary  if  the  epithe- 
lium is  to  maintain  its  integrity  in  organs  the  area  of  whose  free 
surface  is  so  constantly  changing,  as  the  stomach,  lungs,  &c. 
Thus,  if  there  be  but  a  single  layer  of  cells,  as  in  the  epithelium 
lining  the  air  vesicles  of  the  lungs,  the  stretching  of  this  mem- 
brane causes  such  a  thinning  out  of  the  cells  that  they  change 
their  shape  from  spheroidal  or  short  columnar,  to  squamous,  and 
vice  versa,  when  the  membrane  shrinks. 

Classification   of  Epithelial    Cells. 

Epithelial  cells  may  be  conveniently  classified  as  : 
i.  Squamo2cs,  scaly,  pavement,  or  tesselated. 

2.  Spheroidal,  glandular,  or  polyhedral. 

3.  Columnar,  cylindrical,  conical,  or  goblet-shaped. 

4.  Ciliated. 

5.  Transitional. 


CHAP.  III.] 


EPITHELIAL    CELL- 


23 


Although,  for  convenience,  epithelial  cells  are  thus  classified, 
yet  tin-  first  three  forms  of  cells  arc  sometimes  met  with  at 
different  depths  in  the  same  membrane.     Ajs  an  example  of  such 


Fig.  11. —  V  m  of  Babbit? s  cornea,    a.  Anterior  epithelium,  showing  the  different 

shapes  of  the  cells  at  various  depths  from  the  free  surface,    b.  Portion  of  the  substance 
of  cornea.     (Klein.) 


a  laminated  epithelium  showing  these  different  cell-forms  at 
various  depths,  we  may  select  the  anterior  epithelium  of  the 
cornea  (fig.  11). 

1.    Squamous    .Epithelium  (fig.    12). — Arranged   (a)   in   several 
superposed  layers  (stratified  or  laminated),  this  form  of  epithelium 
covers  (a)  the  skin,  where  it  is  called  the  Epidermis,  and  lines  (b) 
tin1  mouth,  pharynx,  and  oesopha- 
gus, (c)  the  conjunctiva,  (d)  the 
vagina,     and     entrance     of    the 
urethra  in  both  sexes  ;  while,  as 
(b)  a  single  layer,  the  same  kind 
of  epithelium  forms  (a)  the  pig- 
mentarv  layer  of  the  retina,  and 
lines  (b)  the  interior  of  the  serous 
and  synovial  sacs,  and  (c)  of  the 
heart,   blood-  and  lymph-vessels 

(Endothelium).  It  consists  of  cells,  which  are  flattened  and 
scaly,  with  an  irregular  outline  :  and,  when  laminated,  may 
form  a  dense  horny  investment,  as  on  parts  of  the  palms  of  the 
hands  and  soles  of  the  feet.  The  nucleus  is  often  not  apparent. 
The  really  cellular  nature  of  even  the  dry  and  shrivelled  scales 
cast  off  from  the  surface  of  the  epidermis,  can  be  proved  by  the 
application  of  caustic  potash,  which  causes  them  rapidly  to  swell 
and  assume  their  original  form. 


Fig.  12. — Squamous  epithelium  scales  from 
the  inside  of  the  mouth.  X  260. 
(Henle.) 


24 


STRUCTURE    OF    ELEMENTARY    TISSUES.        [chap.  hi. 


Squamous  cells  are  generally  united  by  an  intercellular  sub- 
stance ;  but  in  many  of  the  deeper  layers  of  epithelium  in  the 
mouth  and  skin,  the  outline  of  the  cells  is  very  irregular. 

Such  cells  (fig.  13)  are  termed  "ridge  and  furrow,"  "  cogged"  or 

" prickle"  cells.  These  "  prickles" 
are  prolongations  of  the  intra- 
cellular network  which  run  across 
from  cell  to  cell,  thus  joining  them 
together,  the  interstices  being 
filled  by  the  transparent  inter- 
cellular cement  substance.  "When 
this  increases  in  quantity  in  in- 
flammation, the  cells  are  unshed 
further  apart  and  the  connecting 
fibrils  or  "prickles"  elongated, 
and  therefore   more  clearly  visi- 


Fig.  13. — Jagged  cells  of  the  middle  layers 
of  pavement  epithelium,  from  a  vertical 
section  of  the  gum  of  a  newborn 
infant.    (Klein.) 


ble. 


H 


Squamous  epithelium,  e.g.  the  pigment  cells  of  the  retina,  may 

have  a  deposit  of  pigment  in 
the  cell-substance.  This  pig- 
ment consists  of  minute  mole- 
cules of  melanin,  imbedded  in 
the  cell-substance  and  almost 
concealing  the  nucleus,  which 
is  itself  transparent  (fig.  14). 

In  white  rabbits  and  other 
albino   animals,  in  which  the 
pigment  of  the  eye  is  absent, 
this  layer  is  found  to  consist 
of  colourless  pavement  epithe- 
lial cells. 
Endothelium — The    squamous  epithelium  lining  the  serous 
membranes,  and  the  interior  of  blood-vessels,  presents  so  many 
special  features  as  to  demand  a  special  description  ;  it  is  called  by 
a  distinct  name — Endothelium. 

The  main  points  of  distinction  above  alluded  to  are,  1.  the  very 
flattened  form  of  these  cells  ;  2.  their  constant  occurrence  in  only 
a  single  layer;  3.  the  fact  that  they  are  developed  from  the 
"  mesoblast,"  while  all  other  epithelial   cells  are  derived  from  the 


.  14. —  Pigment  cells  from  Oc  retina. 
A,  cells  still  cohering,  seen  on  their  sur- 
face ;  a,  nucleus  indistinctly  seen.  In  the 
other  cells  the  nucleus  is  concealed  by 
the  pigment  granules.  B,  twp  cells  seen 
in  pronle  ;  a,  the  outer  or  posterior  part 
containing  scarcely  any  pigment,  x  370. 
(Henle.) 


<H  LP.  III. J 


END01  BELIUM. 


^5 


11  epiblast,"  or  "  hypoblast  ;  '*  4.  they  line  closed  cavities  not  com- 
municating with  the  exterior  of  the  body.  Endothelial  cells  form 
an  important  and  well-defined  Bub-division  of  squamous  epithelial 
cells,  which  has  been  especially  studied  during  the  last  few  3 
Their  examination  has  been  much  facilitated  by  the  adoption  of 
the  methyl  of  Btaining  serous  membranes  with  Bilver  nitrate. 


Fig.  15. — Part  of  the  omentum  of  a  cat,  stained  in  .silver  nitrate,  x  100.  The  tissue  forms  a 
embramef  that  is  to  say,  one  "which  is  studded  with  holes  or  window-. 
In  the  figure  these  are  of  various  shapes  and  sizes,  leaving  trabecule,  the  basis  i  if 
which  is  fibrous  tissue.  The  trabecule  are  of  various  sizes,  and  are  covered  with 
endothelial  cells,  the  nuclei  of  which  have  been  made  evident  by  staining  with  hema- 
toxylin after  the  silver  nitrate  has  outlined  the  cells  by  staining  the  intercellular 
substance.    ,V.  I).  Hai. 


When  a  small  portion  of  a  perfectly  fresh  serous  membrane.  - 
the  mesentery  or  omentum  (fig.  15),  is  immersed  for  a  few  minutes  in 
a  quarter  per  cent,  solution  of  this  re-agent,  washed  with  water  and 
exposed  to  the  action  of  light,  the  silver  oxide  is  precipitated  along 
the  boundaries  of  the  cells,  and  the  whole  surface  is  found  to  be 
marked  out  with  exquisite  delicacy,  by  fine  dark  lines,  into  a 
number  of  polygonal  spaces  (endothelial  cells)  (figs.  15  and  16). 

Endothelium  lines,  as  before  mentioned,  all  the  serous  cavities 
of  the  body,  including  the  anterior  chamber  of  the  eye,  also  the 
synovial  membranes  of  joints,  and  the  interior  of  the  heart  and  of 


26 


STRUCTURE    OF    ELEMENTARY    TISSUES.        [chap.  hi. 


all  blood-vessels  and  lymphatics.     It  forms  also  a  delicate  investing 
sheath  for  nerve-fibres  and  peripheral  ganglion-cells.    The  cells  are 


j-jo.  16. — Abdominal  surface  of  centrum  tendineum  of  diaphragm  of  rabbit,  showing  the  general 
polygonal  shape"  of  the  endothelial  cells :  each  is  nucleated.    (Klein.)     x  300. 

scaly  in  form,  and  irregular  in  outline  ;  those  lining  the  interior  of 
"blood-vessels  and  lymphatics  having  a  spindle-shape  with  a  very 


Fie-  17  —Silver-stained  preparation  of  great  omentum  of  dog,  which  shows,  amongst  the 
flat'endothelium  of  the  surface,  small  and  large  groups  of  germinating  endothelium, 
between  which  numbers  of  stomata  are  to  be  seen.    (Klein.)    x  300. 

wavy  outline.     They  enclose  a  clear,  oval  nucleus,  which,  when 
the  cell  is  viewed  in  profile,  is  seen  to  project  from  its  surface. 


CHAP.  III.] 


ENDOTHELIUM. 


27 


Endothelial  cells  may  be  ciliated,  e.g.,  those  in  the  mesentery  of 
frogs,  especially  about  the  breeding  season. 

Besides  the  ordinary  endothelial  cells  above  described,  there  are 

found  on  the  omentum  and  parts  of  the  pleura  of  many  animals, 
little  bud-like  processes  or  nodules,  consisting  of  small  polyhedral 
granular  cells,  rounded  on  their  free  surface,  which  multiply  very 
rapidly  by  division  (fig.  17).  These  constitute  what  is  known  as 
"germinating  endothelium."  The  process  of  germination  doubt- 
less goes  on  in  health,  and  the  small  cells  which  are  thrown  off  in 
succession  are  carried  into  the  lymphatics,  and  contribute 
to  the  number  of  the  lymph  corpuscles.  The  buds  may  be 
enormously  increased  both  in  number  and  size  in  certain  diseased 
conditions. 

On  those  portions  of  the  peritoneum  and  other  serous  membranes 
where  lymphatics  abound,  there  are  numerous  small  orifices — ■ 
stomata — (fig.  18)   between  the  endothelial  cells  :  these  are  really 


\  ^  n 


^\ 


Fig.  18. — Peritoneal  surface  of  septum  cisternal  hjmpJiaticce  marjn(e  of  fro rj.  The  stomata, 
some  of  which  are  open,  some  collapsed,  are  surrounded  by  germinating  endothelium. 
(Klein.)     x  160. 


the  open  mouths  of  lymphatic  vessels,  and  through  them  lymph- 
corpuscles,  and  the  serous  fluid  from  the  serous  cavity,  pass  into 
the  lymphatic  system. 

2.  Spheroidal  epithelial  cells  are  the  active  secreting  agents  in 
most  secreting  glands,  and  hence  are  often  termed  glandular  : 
they  are  generally  more  or  less  rounded  in  outline  :  often  poly- 
gonal from  mutual  pressure. 


28 


STRUCTURE    OF    ELEMENTARY    TISSUES.        [chap,  hi. 


Excellent  examples  are  to  be  found  in  the  liver,  the  secreting 
tubes  of  the  kidney,  and  in  the  salivary  and  peptic  glands 
(fig.  19). 


Fig.  19. — Glandular  epithelium.    A.  small  lobule  of  a  mucous  gland  of  the  tongue,  showing 
nucleated  glandular  spheroidal  cells.    B.  Liver  cells,     x  200.     (V.  D.  Harris.) 

3.   Columnar  epithelium  (fig.  20,  a  and  b)  lines  (a.)  the  mucous 
membrane  of  the  stomach  and  intestines,  from  the  cardiac  orifice  of 


fc- 


Fig.  20. — A.  V-  of  the  small  intestine  of  a  cat.    a.  Striated  basilar 

border  of  the  epithelium.  I.  Columnar  epithelium.  <•.  Goblet  cells,  d.  Central 
lymph-vessel,  e.  Smooth  muscular  fibres,  f.  Adenoid  stroma  of  the  villus  in  which 
lymph  corpuscles  lie.    B.  Gobiet-eeUa.    ;Klein.) 

the  stomach  to  the  anus,  and  (b.)  wholly  or  in  part  the  ducts  of 
the  glands  opening  on  its  free  surface  ;  also  (c.)  many  gland-ducts 
in  other  regions  of  the  body,  e.g.,  mammary,  salivary,  he.  ;  (d.)  the 


<H.vr.  in.]      .     I  r-CELLS  :   CILIATED   CELLfi 

cells  which  form  the  s  of  the  epithelial  lining  of  the 

trachea  are  approximately  columnar. 

I:  "t*  cells  which  are  cylindrical  or  prismatic  in  form, 

and  contain  a  large  oval  nucleus.     When  evenly  packed  Bide  by 
side  as  a  sins  uniformly  columnar:  hut  when 

occurring  in  several  layer-  as  in  the  d<  strata  of  the  epithelial 

lining  of  the  trachea,  their  shape     -    \  ry   variable,  an<l 
departs  very  widely  from  the  typical  columnar  form. 

. — Many  cylindrical  epithelial  cells  and  _  curious 
transformation,  and  from  the  alteration  in  their  shape  are  termed 
_      let-cell-       _._:.         .    md  b). 

These  are  never   seen    in   a  perfectly  fresh    specimen  :    but  if 
such  a  specimen  be  watched  for  some  time,  little  kn<>b>  are 
gradually  appearing  on  the  free  surface  of  the  epithelium,  and  are 
finally  detached  :  these  consist  of  the  cell-contents  which  ar 
charged  by  the    open  mouth  of  the  goblet,  leaving   the  nucleus 
surrounded  by  the  remains  of  the  protoplasm  in  its  narrow  stem. 

_      L  this  transformation  as  a  normal  process  which  is 
continually  going  on  during  life,  the  discharged   cell-contents  con- 
tributing to  form  mucus,  the  cells  being  supposed  in  many      -  -  - 
recover  their  original  shape. 

The  columnar  epithelial  cells  of  the  alimentary  canal  pose 
structureless  layer  on  their  free   surface  :  such  a  layer,  appearing 
striated  when  viewed  in  section,  is  termed  the   ;*  striated  basilar 
border  "  (tig.  20,  a. 

4.   (         led  cells  are   generally  cylindrical  (fig.  21.  b),  but  may 
r  even  almost  squamous  in  shape  (liu'.  21. 

This  form  of  epithelium  lines  (a.)  the  whole  of  the  respiratory 
tract  from  the  larynx  to  the  finest  sub-divisions  of  the  bronchi, 
-lie   lower  parts  of  the   nasal    pa—  ges,   and   some  portions 
of  the  generative   apparatus — in  the  male  (b.)  lining  tl 
efferentia  "  of  the   testicle,  and  their  prol     stations  at  -  the 

lower  end  of  the  epididymis  :  in  the  feinak  .nmencinu-  about 

the  middle  of  the  neck  of  the  uterus,  and  extending  throughout 
the  uterus  and  Fallopian  tubes  to  their  fimbriated  extremities, 
and  even  for  a  short  distance  on  the  peritoneal  surface  of  the 
latter,  (d.)  The  ventricles  of  the  brain  and  the  central  canal  of 
spina]  cord  are  clothed  with  ciliated  epithelium  in  the  child, 
but  in  the  adult  it  is  limited  to  the  central  canal  of  the  cord. 


30 


STRUCTURE    OF    ELEMENTARY    TISSUES.        [chap.  hi. 


The  Cilia,  or  fine  hair-like  processes  which    give   the  name  to 
this  variety  of  epithelium,  vary  a  good  deal  in   size  in  different 


Fig.   21.— A.  Spheroidal  ciliated  cells  from  the  mouth  of    the  frog.      X  300  diameters. 
(Sharpey.) 
B.  a.  Ciliated  columnar  epithelium  lining  a  bronchus,      h.    Branched  connective-tissue 
corpuscles.    (Klein  and  Noble  Smith.) 


classes  of  animals,  being  very  much  smaller  in  the  higher  than 
among  the  lower  orders,  in  which  they  sometimes  exceed  in  length 
the  cell  itself. 

The  number  of  cilia  on  any  one  cell  ranges  from  ten  to  thirty, 
and  those  attached  to  the  same  cell  are  often  of  different  lengths. 
When  living  ciliated  epithelium,  e.g.,  the  gill  of  a  mussel,  is  ex- 
amined under  the  microscope,  the  cilia  are  seen  to  be  in  constant 
rapid  motion ;  each  cilium  being  fixed  at  one  end,  and  swinging  or 
lashing  to  and  fro.  The  general  impression  given  to  the  eye  of  the 
observer  is  very  similar  to  that  produced  by  waves  in  a  field  of 
corn,  or  swiftly  running  and  rippling  water,  and  the  result  of  their 
movement  is  to  produce  a  continuous  current  in  a  definite 
direction,  and  this  direction  is  invariably  the  same  on  the  same 
surface,  being  always,  in  the  case  of  a  cavity,  towards  its  external 
orifice. 

5.  Transitional  Epithelium. — This  temi  has  been  applied  to  cells 
which  are  neither  arranged  in  a  single  layer,  as  is  the  case  with 
simple  epithelium,  nor  yet  in  many  superimposed  strata  as  in  lami- 
nated ;  in  other  words,  the  term  is  employed  when  epithelial  cells 
are  found  in  two,  three,  or  four  superimposed  layers.  The  upper 
layer  may  be  either  columnar,  ciliated,  or  squamous.  "When  the 
upper  layer  is  columnar  or  ciliated,  the  second  layer  consists  of 
smaller  cells  fitted  into  the  inequalities  of  the  cells  above  them,  as 
in  the  trachea  (fig.  21,  b).  The  epithelium  which  is  met  with  lining 
the  urinary  bladder  and  ureters  is,  however,  the  transitional  par 


OB  LP.   in.  | 


TRANSITIONAL    EPITHELIUM. 


31 


excellence.     In  this  variety  there  are  two  or  three  layers  of  cells, 
the  upper  being  more  or  less  flattened  according  to  the  full  or 


Fig.  22.— E 'pith Hum  of  th>   bladder;  a,  one  of  the  cells  of  the  first  row;  l>,  a  cell  of  the 
second  row ;  c,  cells  in  situ,  of  first,  second,  and  deepest  layers.     (Obersteiner.) 

collapsed  condition  of  the  organ,  their  under  surface  being  marked 
with  one  or  more  depressions,  into  which  the  heads  of  the  next 
layer  of  club-shaped  cells  fit.     Between  the  lower  and  narrower 


Fig.  23.—  Transitional  epithelial  cells  from  a  scraping  of  the  mucous  membrane  of  the 
bladder  of  the  rabbit.     (V.  D.  Harris.) 

parts  of  the  second  row  of  cells,  are  fixed  the  irregular  cells  which 
constitute  the  third  row,  and  in  like  manner  sometimes  a 
fourth  row  (fig.  22).  It  can  be  easily  understood,  therefore, 
that  if  a  scraping  of  the  mucous  membrane  of  the  bladder  be 
teazed,  and  examined  under  the  microscope,  cells  of  a  great  variety 
of  forms  may  be  made  out  (fig.  23).  Each  cell  contains  a  large 
nucleus,  and  the  larger  and  superficial  cells  often  possess  two. 

Special  Epithelium  in  Organs  of  Special  Sense. — In 
addition  to  the  above  kinds  of  epithelium,  certain  highly  specialized 
forms  of  epithelial  cells  are  found  in. the  organs  of  smell,  sight, 
and  hearing,  viz.,  olfactory  cells,  retinal  rods  and  cones,  auditory 
cells  ;  they  will  be  described  in  the  chapters  which  deal  with  their 
functions. 


32  STRUCTURE    OF    ELEMENTARY    TISSUES.        [chap.  hi. 

Functions    of   Epithelium According  to  function,  epithelial 

cells  may  be  classified  as  : — 

(i.)  Protective,  e.g.,  in  the  skin,  mouth,  blood-vessels,  &c. 

(2.)  Protective  and  moving — ciliated  epithelium. 

(3.)  Secreting — glandular  epithelium  ;  or,  Secreting  formed  ele- 
ments— epithelium  of  testicle  secreting  spermatozoa. 

(4.)  Protective  and  secreting,  e.g.,  epithelium  of  intestine. 

(5.)  Sensorial,  e.g.,  olfactory  cells,  rods  and  cones  of  retina, 
organ  of  Corti. 


Epithelium  forms  a  continuous  smooth  investment  over  the 
whole  body,  being  thickened  into  a  hard,  horny  tissue  at  the  points 
most  exposed  to  pressure,  and  developing  various  appendages,  such 
as  hairs  and  nails,  whose  structure  and  functions  will  be  considered 
in  a  future  chapter.  Epithelium  lines  also  the  sensorial  surfaces 
of  the  eye,  ear,  nose,  and  mouth,  and  thus  serves  as  the  medium 
through  which  all  impressions  from  the  external  world — touch, 
smell,  taste,  sight,  hearing — reach  the  delicate  nerve-endings, 
whence  they  are  conveyed  to  the  brain. 

The  ciliated  epithelium  which  lines  the  air-passages  serves  not 
only  as  a  protective  investment,  but  also  by  the  movements  of 
its  cilia  is  enabled  to  propel  fluids  and  minute  particles  of  solid 
matter  so  as  to  aid  their  expulsion  from  the  body.  In  the 
case  of  the  Fallopian  tube,  this  agency  assists  the  progress  of 
the  ovum  towards  the  cavity  of  the  uterus.  Of  the  purposes 
served  by  cilia  in  the  ventricles  of  the  brain,  nothing  is  known. 
(For  an  account  of  the  nature  and  conditions  of  ciliary  motion, 
see  chapter  on  Motion.) 

The  epithelium  of  the  various  glands,  and  of  the  whole  intes- 
tinal tract,  has  the  power  of  secretion,  i.e.,  of  chemically  trans- 
forming certain  materials  of  the  blood  ;  in  the  case  of  mucus  and 
saliva  this  has  been  proved  to  involve  the  transformation  of  the 
epithelial  cells  themselves ;  the  cell-substance  of  the  epithelial 
cells  of  the  intestine  being  discharged  by  the  rupture  of  their 
envelopes,  as  mucus. 

Epithelium  is  likewise  concerned  in  the  processes  of  transuda- 
tion, diffusion,  and  absorption. 

It  is  constantly  being  shed   at  the  free  surface,  and  reproduced 


ohap.  in.]  THE  CONNECTIVE  TISSUES. 


33 


in  the  deeper  Livers.  The  various  stages  of  its  growth  and  de- 
velopment can  be  well  soon  in  a  BOCtion  of  any  laminated  epithe- 
lium, such  as  the  epidermis. 


The  Connective  Tissues. 

This  group  of  tissues  forms  the  Skeleton  with  its  various  con- 
nections— bones,  cartilages,  and  ligaments — and  also  afford-  a 
supporting  framework  and  investment  to  various  organs  composed 
of  nervous,  muscular,  and  glandular  tissue.  Its  chief  function  is 
the  mechanical  one  of  support,  and  for  this  purpose  it  is  so  inti- 
mately interwoven  with  nearly  all  the  textures  of  the  body,  that 
if  all  other  tissues  could  be  removed,  and  the  connective  tissues 
left,  we  should  have  a  wonderfully  exact  model  of  almost 
every  organ  and  tissue  in  the  body,  correct  even  to  the  smallest 
minutiae  of  structure. 

Classification  of  Connective  Tissues. — The  chief  varieties 
of  connective  tissues  may  be  thus  classified  : — 

I.  The  Fibrous  Connective  Tissues. 

A. — Chief  Forms. 

a.  Areolar. 

b.  White  fibrous. 

c.  Elastic. 

B. — Special  Varieties. 

a.  Gelatinous. 

I.  Adenoid  or  Retiform. 

c.  Neuroglia. 

d.  Adipose. 

II.  Cartilage. 

III.  Bone. 

All  of  the  varieties  of  connective  tissue  are  made  up  of  two 
parts,  namely,  cells  and  intercellular  suhstance. 

Cells. — The  cells  are  of  two  kinds. 

(a.)  Fixed. — These  are  cells  of  a  flattened  shape,  with  branched 
processes,  which  are  often   united  together  to  form  a  network : 

D 


34 


STRUCTURE   OF  ELEMENTARY   TISSUES.        [chap.  in. 


they  can  be  most  readily  observed  in  the  cornea  in  which  they  are 
arranged,  layer  above  layer,  parallel  to  the  free  surface.  They  lie 
in  spaces,  in  the  intercellular  or  ground  substance,  which  are  of 
the  same  shape  as  the  cells  they  contain  but  rather  larger,  and 
which  form  by  anastomosis  a  system  of  branching  canals  freely 
communicating  (fig.  24). 


Fig.  24. — HorizontaZ'preparation  of  cornea  of  frog,  stained  in  gold  chloride;  sho\ring  the 
network  of  branched  cornea  corpuscles.  The  ground-substance  is  completely  colour- 
less,    x  400.     (Klein.) 


To  this  class  of  cells  belong  the  flattened  tendon  corpuscles 
which  are  arranged  in  long  lines  or  rows  parallel  to  the  fibres 
(fig.  29). 

These  branched  cells,  in  certain  situations,  contain  a  number 
of  pigment-granules,  giving  them  a  dark  appearance  :  they  form 
one  variety  of  pigment-cells.  Branched  pigment-cells  of  this 
kind  are  found  in  the  outer  layers  of  the  choroid  (fig.  25).  In 
many  lower  animals,  such  as  the  frog,  they  are  found  widely 
distributed,  not  only  in  the  skin,  but  also  in  many  internal  parts, 
e.g.,  the  mesentery  and  sheaths  of  blood-vessels.  In  the  web 
of  the  frog's  foot  such  pigment -cells  may  be  seen,  with  pig- 
ment evenly  distributed  through  the  body  of  the  cell  and  its 
processes  ;  but  under  the  action  of  light,  electricity,  and  other 
stimuli,  the  pigment-granules  become  massed  in  the  body  of  the 
cell,  leaving  the  processes  quite  hyaline ;  if  the  stimulus  be 
removed,  they  will  gradually  be  distributed  again  all  over  the 


OHAP.  ill.] 


CONNECTIVE  TISSUE. 


35 


processes.      Thus  the  skin  in  the  frog  is  sometimes   uniformly 
dusky,    and    sometimes   quite   light-coloured,    with    isolated    dark 
spots.       In    the    choroid    and 
retina  the  pigment-cells  absorb 
light. 

(o.)  Amwhoid  cells,  of  an 
approximately  spherical  shape: 
they  have  a  great  general 
resemblance  to  colourless  blood 
corpuscles  (fig.  2),  with  which 
some  of  them  arc  probably 
identical.  They  consist  of  finely 
granular  nucleated  protoplasm, 
and  have  the  property,  not 
only  of  changing  their  form, 
but  also  of  moving  about, 
whence  they  are  termed  mi- 
gratory. They  are  readily  dis- 
tinguished from  the  branched  connective-tissue  corpuscles  by 
their  free  condition,  and  the  absence  of  processes.  Some  are 
much  larger  than  others,  and 
are    found    especially  in    the 


Fig.    25.  —  Ramified     pigment  -  ceUe, 

from  "the  tissue  of  the  choroid  coat 
of  the  eye.  x  350.  a,  cell  with 
pigment ;  b,  colourless  fusiform  cells. 
(Kolliker.) 


sublingual  gland  of   the 


dog 


and  guinea  pig  and  in  the 
mucous  membrane  of  the  in- 
testine. A  second  variety  of 
these  cells  called  plasma  cells 
(Waldeyer)  are  larger  than 
the  amoeboid  cells,  apparently 
granular,  less  active  in  their 
movements.  They  are  chiefly 
to  be  found  in  the  inter- 
muscular septa,  in  the  mucous 
and  submucous  coats  of  the 
intestine,  in  lymphatic  glands. 
and  in  the  omentum. 


Fig 


26.  —  Flat,  pigmented,  branched,  con- 
nective-tissue celh  from  the  sheath  of  a 
large  blood-vessel  of  frog's  mesentery : 
the  pigment  is  not  distributed  uniformly 
through  the  substance  of  the  larger  cell, 
consequently  some  parts  of  the  cell  look 
blacker  than  others  (uncontracted  state). 
In  the  two  smaller  cells  most  of  the  pig- 
ment is  withdrawn  into  the  cell-body,  so 
that  thev  appear  smaller,  blacker,  and 
less  branched,  x  350.  (Klein  and  Noble 
Smith.) 


Intercellular  Substance. 

—This  may  be   fibrillar,  as   in   the    fibrous   tissues   and    certain 
varieties  of  cartilage  ;  or  homogeneous*  as  in  hyaline  cartilage 


d  2 


36 


STRUCTURE   OF  ELEMENTARY  TISSUES.        [chap.  nr. 


The  fibres  composing  the  former  are  of  two  kinds — (a.)  White 

fibres,      (b.)  Yellow  elastic  fibres. 

(a.)   White  Fibres. — These  are  arranged  parallel  to  each  other 

in  wavy  bundles  of  various  sizes  :  such  bundles  may  either  have 

a  parallel  arrangement  (fig.  27),  or 
may  produce  quite  a  felted  texture 
by  their  interlacement.  The  indi- 
vidual fibres  composing  these  fasci- 
culi are  homogeneous,  unbranched, 
and  of  the  same  diameter  through- 
out. They  can  readily  be  isolated 
by  macerating  a  portion  of  white 
fibrous  tissue  {e.g.,  a  small  piece  of 
tendon)  for  a  short  time  in  lime, 
or  baryta-water,  or  in  a  solution  of 
common  salt,  or  potassium  perman- 
ganate :  these  reagents  possessing 
the  power  of  dissolving  the  ce- 
menting interfibrillar  substance 
(which     is     nearly     allied    to    syn- 

tonin),  and  thus  separating  the  fibres  from  each  other. 

(b.)  Yellow  Elastic  Fibres  (fig.  28)  are  of  all  sizes,  from  ex- 
cessively fine  fibrils  up  to  fibres 
of  considerable  thickness  :  they  are 
distinguished  from  white  fibres 
by  the  following  characters  :— 
(1.)  Their  great  power  of  re- 
sistance even  to  the  prolonged 
action  of  chemical  reagents,  e.g., 
Caustic  Soda,  Acetic  Acid,  &c.  (2.) 
Their  well-defined  outlines.  (3.) 
Their  great  tendency  to  branch  and 
form  networks  by  anastomosis. 
(4.)  They  very  often  have  a  twisted 
corkscrew-like  appearance,  and  their 
free  ends  usually  curl  up.  (5.)  They 
are    of  a   yellowish   tint    and  very 

Fig.  28. — Elastic  fibres  from  the  liga-        elastic 
menta  aubflava.  x  200.  (Sharpey.) 


Fig.  27. —  Fibrous  tissue  of 
cornea,  showing  bundles 
of  fibres  with  a  few  scat- 
tered fusiform  cells  lying 
in  the  inter-fascicular 
spaces,  x  400.  (Klein 
and  Noble  Smith.) 


p.  in. J  PIB]  TIVE   T.  37 

Varieties  of  Connective  Tissue. 

I.    Viva,      b    I    ■nnectivk  T 

A. — Chief  F  r  is.— 

Dist  i     lion. — This   variety  has   a    very    wi<le   distribution,  and 

the  subcutaneous,  subserous  and  -ubmucous tissue.    It 

is  found  in  the  mucous  membranes,  in  the  true  skin,  in  the  outer 

-lis  of  the  blood-vessels.     It  forms  sheaths  for  muscles,  net 
glands,  and  the  internal  organs,  ami,  penetrating  into  their  interior, 
supports  and  connects  the  finest  parts. 

Structure, — To  the  naked  eye  it  appears,  when  stretched  out, 
fleecy,  white,  and  soft  meshwork  of  fine  fibrils,  with  here 
and  there  wider  films  joining  in  it.  the  whole  tissue  being 
evidently  elastic.  The  openness  of  the  meshwork  varies 
with  the  locality  from  which  the  specimen  is  taken.  On  the 
addition  of  acetic  acid  the  tissue  swells  up,  and  becomes  gela- 
tinous in  appearance.  Under  the  microscope  it  is  found  to  be 
made  up  of  tine  white  fibres,  which  interlace  in  a  most  irregular 
manner,  together  with  a  variable  number  of  elastic  fibres.  These 
latter  resist  the  action  of  acetic  acid  as  above  mentioned,  so  that 
when  this  reagent  is  added  to  a  specimen  of  areolar  t>- 
although  the  white  fibres  swell  up  and  become  homogeneous, 
certain  elastic  fibres  may  still  be  seen  arranged  in  various 
directions,  sometimes  even  appearing  to  pass  in  a  more  or 
circular  or  in  a  spiral  manner  round  a  small  mass  of 
gelatinous  mass  of  changed  white  fibres.  The  cells  of  the 
tissue  are  arranged  in  no  very  regular  manner,  being 
tained  in  the  spaces  (areolae)  between  the  fibres.  They  com- 
municate, however,  with  one  another  by  their  branched  pro- 
-,  and  also  apparently  with  the  cells  forming  the  walls  of 
the    capillary  blood-vessels    in   their   neighbourhood,   connecting 

ther  the  fibrils   in   a  certain  amount  of   albuminou- 
substance. 

(6.)   White  Fibrous  Ti^m*. 

Distribution. — Typically  in  tendon ;    in  ligaments,  in  the  peri- 


33 


STRUCTURE   OF  ELEMENTARY  TISSUES.         [chap.  hi. 


osteum  and  perichondrium,  the  dura  mater,  the  pericardium,  the 
sclerotic  coat  of  the  eye,  the  fibrous  sheath  of  the  testicle  ;  in  the 
fasciae  and  aponeurosis  of  muscles,  and  in  the  sheaths  of  lymphatic 
glands. 

Structure. — To  the  naked  eye,  tendons  and  many  of  the  fibrous 
membranes,  when   in  a  fresh  state,  present  an  appearance  as  of 

watered  silk.     This  is  due 
to  the  arrangement  of  the 
fibres     in     wavy    parallel 
bundles.      Under  the  mi- 
croscope, the  tissue  appears 
to    consist   of  long,   often 
parallel,  wavy  bundles  of 
fibres    of   different     sizes. 
Sometimes  the  fibres  inter- 
sect each  other.     The  cells 
in  tendons  are  arranged  in 
long  chains  in  the  ground 
substance   separating    the 
bundles  of  fibres,  and  are 
more    or     less     regularly 
quadrilateral    with     large 
round  nuclei  containing  nucleoli,  which  are  generally  placed  so  as 
to  be  contiguous  in  two  cells.     The  cells  consist  of  a  body,  which 
is  thick,  from  which  processes  pass  in  various  directions  into,  and 
partially  filling  up  the  spaces  between  the  bundles  of  fibres.     The 
rows  of  cells  are  separated  from  one  another  by  lines  of  cement 
substance.     The  cell  spaces  can  be  brought  into  view  by  silver 
nitrate.     The  cells  are  generally  marked  by  one  or  more  lines  or 
stripes  when  viewed   longitudinally.     This  appearance  is  really 
produced  by  the  laminar  extension  either  projecting  upwards  or 
downwards. 

(c.)   Yelloio  Elastic  Thsue. 

Distribution. — In  the  ligamentum  nucha?  of  the  ox,  horse, 
and  many  other  animals  ;  in  the  ligamenta  subflava  of 
man  ;  in  the  arteries,  constituting  the  fenestrated  coat  of 
Henle  ;  in  veins  ;  in  the  lungs  and  trachea ;  in  the  stylo-hyoid, 
thyro-hyoid,  and  crico-thyroid  ligaments ;  in  the  true  vocal 
cords. 


Fig.  29. — CauAdk  tendon  of  young  rat,  shewing  the 
arrangement,  form,  and  structure  of  the  tendon 
cells.     X  300.    (Klein.) 


cil.w.  III.] 


FIBROUS   CONXECTIVK   TISSUES. 


39 


Structure.  —  Elastic  tissue  occurs  in  various  forms,  from  ;i  struc- 
tureless, elastic  membrane  to  a  tissue  whose  chief  constituents 
ure  bundles  of  elastic  fibres  crossing  each  other  at  different  angles  : 

these  varieties  may  be  classified  as  follows: — 

(((.)  Fine  elastic  fibrils,  which  branch  and  anastomose  to  form  a 
network  :  this  variety  of  elastic  tissue  occurs  chiefly  in  the  skin 
and  mucous  membranes,  in  subcutane- 
ous and  submucous  tissue,  in  the  lungs 
and  true  vocal  cords. 

(b.)  Thick  fibres,  sometimes  cylindri- 
cal, sometimes  flattened  like  tape,  which 
branch  and  form  a  network  :  these  are 
seen  most  typically  m  the  ligamenta 
subflava  and  also  in  the  ligamentuin 
nuchse  of  such  animals  as  the  ox  and 
horse,  in  which  it  is  largely  developed. 

(c.)  Elastic  membranes  with  perfora- 
tions, e.g.,  Henle's  fenestrated  mem- 
brane :  this  variety  is  found  chiefly 
in  the  arteries  and  veins. 

(d.)    CoiltillUOUS,  homogeneous  elastic    Fig.  30.— Transverse  section  of  ten- 

.  don  from  a  cross  section  of  the 

membranes,  e.g.,  Bowman  s  anterior  elas- 
tic lamina,  and  Descemet's  posterior 
elastic  lamina,  both  in  the  cornea. 

A  certain  number  of  flat  connective 
tissue   cells    are  found   in  the   ground 

substance  between  the  elastic  fibres  constituting  this  variety  of 
connective  tissue. 


tail  of  a  rabbit,  showing  sheath, 
fibrous  septa,  and  branched  con- 
nective-tissue corpuscles.  The 
spaces  left  white  in  the  drawing- 
represent  the  tendinous  fibres 
in  transverse  section,  x  250. 
(Klein.) 


B. — Special  Forms. — (a.)  Gelatinous  Tissue. 

Distribution. — Gelatinous  connective  tissue  forms  the  chief  part 
of  the  bodies  of  jelly  fish  ;  it  is  found  in  many  parts  of  the 
human  embryo,  but  remains  in  the  adult  only  in  the  vitreous 
humour  of  the  eye.  It  may  be  best  seen  in  the  last-named  situa- 
tion, in  the  "  Whartonian  jelly  "  of  the  umbilical  cord,  and  in 
the  enamel  organ  of  developing  teeth. 

Structure. — It  consists  of  cells,  which  in  the  vitreous  humour 
are  rounded,  and  in  the  jelly  of  the  enamel  organ  are  stellate, 
imbedded  in  a  soft  jelly-like  inter-cellular  substance  which  forms 


40 


STRUCTURE   OF  ELEMENTARY  TISSUES.         [chap.  hi. 


the    bulk    of    the    tissue,    and    which    contains    a    considerable 
quantity  of  mucin.       In   the    umbilical    cord,   that   part   of  the 

jelly   immediately   surround- 


ing the  stellate  cells  shows 
marks  of  obscure  fibrillation. 

(6.)  Adenoid  or  Retiform. 

Distribution. — It  composes 
the  stroma  of  the  spleen  and 
lymphatic  glands,  and  is 
found  also  in  the  thymus,  in 
the  tonsils,  in  the  follicular 
glands  of  the  tongue,  in 
Peyer's  patches  and  in  the 
solitary  glands  of  the  intes- 
tines, and  in  the  mucous 
membranes  generally. 


Fig.  31. — Tissue  of  the  jelly  of  Wharton  from 
umbilical  cord,  a,  connective-tissue  cor- 
puscles; b,  fasciculi  of  connective  tissue  ; 
c,  spherical  formative  cells.     (Frey.) 


Structure.  —  Adenoid  or 
retiform  tissue  consists  of  a  very  delicate  network  of  minute  fibrils, 
formed  originally  by  the  union  of  processes  of  branched  connective- 


Fig.  32. — Part  of  a  section  of  o  lymphatic  gland,  from  ■which  the  corpuscles  have  been  for  the 
most  part  "removed,  showing  the  adenoid  reticulum.     (Klein  and  Noble  Smith.) 

tissue  corpuscles  the  nuclei  of  which,  however,  are  visible  only 
during  the  early  periods  of  development  of  the  tissue  (fig.  32). 


niAF.  in.]       DEVELOPMENT  OF  FIBROUS  TISSUES.  41 

The  nuclei  found  on  the  fibrillar  meshwork  <1«»  not  form  an 
essential  part  of  it.  The  fibrils  are  neither  white  fibrous  nor 
elastic  tissue,  as  they  are  insoluble  in  boiling  water,  although 

readily  soluble  in  hot  alkaline  solutions. 

(c.)  Neuroglia. — This  tissue  forms  the  support  of  the  Nervous 

elements  in  the  Brain  and  Spinal  cord.  It  consists  of  a  very  fine 
meshwork  of  fibrils,  said  to  be  elastic,  and  with  nucleated  plates 
which  constitute  the  connective-tissue  corpuscles  imbedded  in  it. 

Development  of  Fibrous  Tissues. — In  the  embryo  the 
place  of  the  fibrous  tissues  is  at  first  occupied  by  a  mass  of 
roundish  cells,  derived  from  the  "  mesoblast." 

These  develop  either  into  a  network  of  branched  cells,  or  into 
groups  of  fusiform  cells  (fig.  33). 


Fig.  35. — Portion   of  submucous  tissue  of  gravid  uterus  of  sow.    «,  branched  cells,  more  or 
less  spindle-shaped ;  b,  bundles  of  connective  tissue.     (Klein.) 

The  cells  are  imbedded  in  a  semi-fluid  albuminous  substance 
derived  either  from  the  cells  themselves  or  from  the  neighbouring 
blood-vessels  ;  this  afterwards  forms  the  cement  substance.  In  it 
fibres  are  developed,  either  by  part  of  the  cells  becoming  fibrils,  the 
others  remaining  as  connective-tissue  corpuscles,  or  by  the  fibrils 
being  developed  from  the  outside  layers  of  the  protoplasm  of  the 
cells,  which  grow  up  again  to  their  original  size  and  remain  im- 
bedded among  the  fibres.  This  process  gives  rise  to  fibres  arranged 
in  the  one  case  in  interlacing  networks  (areolar  tissue),  in  the 
other  in  parallel  bundles  (white  fibrous  tissue).  In  the  mature 
forms  of  purely  fibrous  tissue  not  only  the  remnants  of  the  cell- 
substance,  but  even  the  nuclei  may  disappear.  The  embryonic 
tissue,  from  which  elastic  fibres  are  developed,  is  composed  of  fusi- 
form cells,  and  a  structureless  intercellular  substance  by  the 
gradual  fibrillation  of  which  elastic  fibres  are  formed.     The  fusi- 


42  STRUCTURE    OF  ELEMENTARY  TISSUES.         [chap.  hi. 

form  cells  dwindle  in  size  and  eventually  disappear  so  completely 
that  in  mature  elastic  tissue  hardly  a  trace  of  them  is  to  be 
found  :  meanwhile  the  elastic  fibres  steadily  increase  in  size. 

Another  theory  of  the  development  of  the  connective-tissue  fibrils 
supposes  that  they  arise  from  deposits  in  the  intercellular  substance 
and  not  from  the  cells  themselves ;  these  deposits,  in  the  case  of 
elastic  fibres,  appearing  first  of  all  in  the  form  of  rows  of  granules, 
which,  joining  together,  form  long  fibrils.  It  seems  probable  that 
even  if  this  view  be  correct,  the  cells  themselves  have  a  consider- 
able influence  in  the  production  of  the  deposits  outside  them. 

Functions  of  Areolar  and  Fibrous  Tissue. — The  main 
function  of  connective  tissue  is  mechanical  rather  than  vital :  it 
fulfils  the  subsidiary  but  important  use  of  supporting  and  connect- 
ing the  various  tissues  and  organs  of  the  bod}-. 

In  glands  the  trabecule  of  connective  tissue  form  an  interstitial 
framework  in  which  the  parenchyma  or  secreting  gland-tissue  is 
lodged:  in  muscles  and  nerves  the  septa  of  connective  tissue 
support  the  bundles  of  fibres,  which  form  the  essential  part  of 
the  structure. 

Elastic  tissue,  by  virtue  of  its  elasticity,  has  other  important 
uses  :  these,  again,  are  mechanical  rather  than  vital.  Thus  the 
ligamentum  nucha3  of  the  horse  or  ox  acts  very  much  as  an 
India-rubber  band  in  the  same  position  would.  It  maintains  the 
head  in  a  proper  position  without  any  muscular  exertion ;  and 
when  the  head  has  been  lowered  by  the  action  of  the  flexor  mus- 
cles of  the  neck,  and  the  ligamentum  nuchas  thus  stretched,  the 
head  is  brought  up  again  to  its  normal  position  by  the  relaxation 
of  the  flexor  muscles  which  allows  the  elasticity  of  the  ligamentum 
nucha?  to  come  again  into  play. 

(d.)  Adipose  Tissue. 

Distribution. — In  almost  all  regions  of  the  human  body  a  larger 
or  smaller  quantity  of  adipose  or  fatty  tissue  is  present ;  the  chief 
exceptions  being  the  subcutaneous  tissue  of  the  eyelids,  penis,  and 
scrotum,  the  nymphse,  and  the  cavity  of  the  cranium.  Adipose 
tissue  is  also  absent  from  the  substance  of  many  organs,  as  the 
lungs,  liver,  and  others. 

Fatty  matter,  not  in  the  form  of  a  distinct  tissue,  is  also 
widely  present  in  the  body,  e.g.,  in  the  liver  and  brain,  and  in  the 
blood  and  chyle. 


CD  IF.   III. J 


ADIPOSE  TISSUE. 


43 


Adipose  tissue  is  almost  always  found  seated  in  areolar  tissue, 
and  forms  in  its  meshes  little  masses  of  unequal  size  and  irregular 
shape,  to  which  the  term  lobules  is  commonly  applied. 

Structure. — Under  the  microscope  adipose  tissue  is  found  to 
consist  essentially  of  little  vesicles  or  cells  which  present  dark, 
sharply-defined  edges  when  viewed  with  transmitted  light  :  they 

are  about  -^^  or  3-^  of  an  inch  in  diameter,  each  composed  of  a 
structureless  and  colourless  membrane 
or  bag,  filled  with  fatty  matter,  which 
is  liquid  during  life,  but  in  part  soli- 
dified after  death  (fig.  34).  A  nucleus 
is  always  present  in  some  part  or  other 
of  the  cell-wall,  but  in  the  ordinary 
condition  of  the  cell  it  is  not  easily 
or  always  visible. 

This  membrane  and  the  nucleus  can 
generally  be  brought  into  view  by 
staining  the  tissue  :  it  can  be  still 
more  satisfactorily  demonstrated  by 
extracting  the  contents  of  the  fat-cells 

with  ether,  when  the  shrunken,  shrivelled  membranes  remain 
behind.  By  mutual  pressure,  fat-cells  come  to  assume  a  polyhedral 
figure  (fig.  35). 


Fig 


^4. —  Ordinary  fot-ceUs  of  a 
jot  tract  in  the  omentum  of 
a  rat.  (Klein.) 


«s». 


■£i<*.  35. — Group  of  fat-cells  (fc)  with  capillary  vessels  (c).     (Noble  Smith.) 


The  ultimate  cells  are  held  together  by  capillary  blood-vessels 


44 


STRUCTURE   OF  ELEMENTARY  TISSUES.        [chap.  hi. 


(%  35)  >  while  the  little  clusters  thus  formed  are  grouped  into 
small  masses,  and  held  so,  in  most  cases,  by  areolar  tissue. 


Fig.  36. — Blood-vessels  of  adipose  tissue.  A.  Minute  flattened  fat-lobule,  in  ■which  the  vessels 
only  are  represented,  a,  the  terminal  artery;  0,  the  primitive  vein;  b,  the  fat-vesi- 
cles of  one  border  of  the  lobule  separately  represented,  x  100.  b.  Plan  of  the  arrange- 
ment of  the  capillaries  (c)  on  the  exterior  of  the  vesicles  :  more  highly  magnified. 
(Todd  and  Bowman.) 

The  oily  matter  contained  in  the  cells  is  composed  chiefly  of 
the  compounds  of  fatty  acids  with  glycerin,  which  are  named 
oleirij  stearin,  and  palmitin. 

Development  of  Adipose  Tissue. — Fat-cells  are  developed 
from  connective-tissue  corpuscles  :  in  the  infra-orbital  connective- 
tissue  cells  may  be  found  exhibiting  every  intermediate  gradation 
between  an  ordinary  branched  connective-tissue  corpuscle  and  a 
mature  fat-cell.  The  process  of  development  is  as  follows  :  a  few 
small  drops  of  oil  make  their  appearance  in  the  protoplasm  :  by 
their  confluence  a  larger  drop  is  produced  (fig.  37)  :  this  gradually 
increases  in  size  at  the  expense  of  the  original  protoplasm  of  the 
cell,  which  becomes  correspondingly  diminished  in  quantity  till  in 
the  mature  cell  it  only  forms  a  thin  crescent ic  film,  closely  pressed 
against  the  cell-wall,  and  with  a  nucleus  imbedded  in  its  substance 
(figs.  34  and  37). 

Under  certain  circumstances  this  process  may  be  reversed  and 
fat-cells  may  be  changed  back  into  connective-tissue  corpuscles. 
(Kolliker,  Yirchow. ) 


OflAP.  in.] 


ADIPOSE   TISSUE. 


45 


Vessels  and  Serves, — A  large  number  of  blood-vessels  ore  found 
in  adipose  tissue,  which  subdivide  until  each  lobule  of  fat  contains 
a  fine  meshwork  of  capillaries  ensheathing  cadi  individual  fat- 


Fig.  37. — A  lohitle  of  developing  adipose  tissue  from  an  eight  months'  foetus,  a.  Sphe- 
rical or,  from  pressure,  polyhedral  cells  with  large  central  nucleus,  surrounded  by  a 
finely  reticulated  substance  staining  uniformly  with  hematoxylin,  b.  Similar  cells 
with  spaces  from  which  the  fat  has  been  removed  by  oil  of  cloves,  c.  Similar  cells 
showing  how  the  nucleus  with  enclosing  protoplasm  is  being  pressed  towards  peri- 
phery. 0.  Nucleus  of  endothelium  of  investing  capillaries.  (McCarthy.)  Drawn  by 
Treves. 


Fig.  38. — Branched  connective-tissue  corpuscles,  developing  into  fat-cells,     (Klein.) 


globule.     Although  nerve  fibres  pass  through  the  tissue,  no  nerves 
have  been  demonstrated  to  terminate  in  it. 

The  Uses  of  Adipose  Tissue. — Among  the  uses  of  adipose 
tissue,  these  are  the  chief: — 


46  STRUCTURE   OF   ELEMENTARY   TISSUES.        [chap.  hi. 

a.  It  serves  as  a  store  of  combustible  matter  which  may  be  re- 
absorbed into  the  blood  when  occasion  requires,  and,  being  burnt, 
may  help  to  preserve  the  heat  of  the  body. 

b.  That  part  of  the  fat  which  is  situate  beneath  the  skin  must, 
by  its  want  of  conducting  power,  assist  in  preventing  undue  waste 
of  the  heat  of  the  body  by  escape  from  the  surface. 

c.  As  a  packing  material,  fat  serves  very  admirably  to  fill  up 
spaces,  to  form  a  soft  and  yielding  yet  elastic  material  wherewith 
to  wrap  tender  and  delicate  structures,  or  form  a  bed  with  like 
qualities  on  which  such  structures  may  lie,  not  endangered  by 
pressure. 

As  good  examples  of  situations  in  which  fat  serves  such  purposes 
may  be  mentioned  the  palms  of  the  hands  and  soles  of  the  feet, 
and  the  orbits. 

d.  In  the  long  bones,  fatty  tissue,  in  the  form  known  as  yellow 
marrow,  fills  the  medullary  canal,  and  supports  the  small  blood- 
vessels which  are  distributed  from  it  to  the  inner  part  of  the  sub- 
stance of  the  bone. 

II.  Cartilage. 

Cartilage  or  gristle  exists  in  three  different  forms  in  the  human 
body,  viz.,  i,  Hyaline  cartilage,  2,  Yellow  elastic-cartilage,  and 
3,  White  jihro -cartilage. 

Structure  of  Cartilage.— All  kinds  of  cartilage  are  composed  of 
cells  imbedded  in  a  substance  called  the  matrix  :  and  the  apparent 
differences  of  structure  met  with  in  the  various  kinds  of  cartilage 
are  more  due  to  differences  in  the  character  of  the  matrix  than 
of  the  cells.  Among  the  latter,  however,  there  is  also  consider- 
able diversity  of  form  and  size. 

With  the  exception  of  the  articular  variety,  cartilage  is  invested 
by  a  thin  but  tough  firm  fibrous  membrane  called  the  perichon- 
drium. On  the  surface  of  the  articular  cartilage  of  the  foetus,  the 
perichondrium  is  represented  by  a  film  of  epithelium ;  but  this  is 
gradually  worn  away  up  to  the  margin  of  the  articular  surfaces, 
when  by  use  the  parts  begin  to  suffer  friction. 

Nerves  are  probably  not  supplied  to  any  variety  of  cartilage. 

1.  Hyaline  Cartilage. 

Distribution. — This    variety    of  cartilage    is  met   with   largely 


<  H  IP.    III.] 


CAKTILAGE. 


47 


articular  ends  of    bones, 
the    nasal    cartilages,   and 


in   the  human    body — investing  the 
and    forming    the   costal    cartilag 
those  of  the  larynx  with  the  excep- 
tion of  the  epiglottis  and  cornicula 
laryngis.      The    cartilages    of   the 
trachea  and  bronchi  arc  also  hyaline. 

Structure, — Like  other  cartilages 
it  is  composed  of  cells  imbedded 
in  a  matrix.  The  cells,  which  con- 
tain a  nucleus  with  nucleoli,  are 
irregular  in  shape,  and  generally 
grouped  together  in  patches  (fig. 
39).  The  patches  are  of  various 
shapes  and  sizes,  and  placed  at 
unequal  distances  apart.  They 
generally  appear  flattened  near  the 
free  surface  of  the  mass  of  cartilage 
in  which  they  are  placed,  and  more 
or  less  perpendicular  to  the  surface 
in  the  more-deeply  seated  portions. 

The  matrix  of  hyaline  cartilage 
pearance  like  that  of  ground  glass,  and  in  man  and  the  higher 


2*# 

0 


Fig-.  39.  —  Ordinary  hyaline  cartilage 
from  trachea  of  a  child.  The  car- 
tilage cells  are  enclosed  singly  or  in 
paii-s  in  a  capsule  of  hyaline  sub- 
stance, x  150  diams.  "(Klein  and 
Noble  Smith.) 


has   a  dimly    granular   ap- 


Fig.  40. — Freeh  cartilage  from  the  Triton.     (A.  Eollett.) 

animals   has   no   apparent  structure.     In  some  cartilages  of  the 
frog,    however,   even  when    examined    in    the  fresh    state,    it   is 


48  STRUCTURE   OF  ELEMENTARY  TISSUES.        [chap.  hi. 

seen  to  be  mapped  out  into  polygonal  1  (locks  or  cell-territories, 
each  containing  a  cell  in  the  centre,  and  representing  what  is 
generally  called  the  capsule  of  the  cartilage  cells  (fig.  40).  Hya- 
line cartilage  in  man  has  really  the  same  structure,  which  can  be 
demonstrated  by  the  use  of  certain  reagents.  If  a  piece  of  human 
hyaline  cartilage  be  macerated  for  a  long  time  in  dilute  acid  or  in 
hot  water  950 — H3°F.  (350  to  450  C),  the  matrix,  which  pre- 
viously appeared  quite  homogeneous,  is  found  to  be  resolved  into 
a  number  of  concentric  lamella?,  like  the  coats  of  an  onion, 
arranged  round  each  cell  or  group  of  cells.  It  is  thus  shown  to 
consist  of  nothing  but  a  number  of  large  systems  of  capsules 
which  have  become  fused  with  one  another. 

The  cavities  in  the  matrix  in  which  the  cells  lie  are  connected 
together  by  a  series  of  branching  canals,  very  much  resembling 
those  in  the  cornea  :  through  these  canals  fluids  may  make  their 
way  into  the  depths  of  the  tissue. 

In  the  hyaline  cartilage  of  the  ribs,  the  cells  are  mostly  larger 
than  in  the  articular  variety,  and  there  is  a  tendency  to  the 
development  of  fibres  in  the  matrix.  The  costal  cartilages  also 
frequently  become  calcified  in  old  age,  as  also  do  some  of  those  of 
the  larynx.     Fat-globules  may  also  be  seen  in  many  cartilages. 

In  articular  cartilage  the  cells  are  smaller,  and  arranged 
vertically  in  narrow  lines  like  strings  of  beads. 

Temporary  Cartilage. — In  the  foetus,  cartilage  is  the  mate- 
rial of  which  the  bones  are  first  constructed  ;  the  "  model "  of 
each  bone  being  laid  down,  so  to  speak,  in  this  substance.  In 
such  cases  the  cartilage  is  termed  temporary.  It  closely  resembles 
the  ordinary  hyaline  kind ;  the  cells,  however,  are  not  grouped 
together  after  the  fashion  just  described,  but  are  more  uniformly 
distributed  throughout  the  matrix. 

A  variety  of  temporary  hyaline  cartilage  which  has  scarcely  any 
matrix  is  found  in  the  human  subject  only  in  early  foetal  life, 
when  it  constitutes  the  chorda  dorsalis. 

Nutrition  of  Cartilage.  —  Hyaline  cartilage  is  reckoned 
among  the  so-called  non-vascular  structures,  no  blood-vessels  being 
supplied  directly  to  its  own  substance ;  it  is  nourished  by  those 
of  the  bone  beneath.  When  hyaline  cartilage  is  in  thicker  masses, 
as  in  the  case  of  the  cartilages  of  the  ribs,  a  few  blood-vessels 
traverse   its   substance.     The   distinction,    however,  between   all 


ill  W.    III.] 


CARTILAGE. 


49 


so-called  vascular  and  non-vascular  parts,  is  at  the  best  a  very 

artificial  one. 

2.  Yellow  Elastic   Cartilage. 

Distribution. — In  the  external  ear,  in  the  epiglottis  and  cornicula 
laryngis,  and  in  the  Eustachian  tube. 

Structure. — The  cells  are  rounded  or  oval,  with  well-marked 
nuclei  and  nucleoli  (fig.  41).  The  matrix  in  which  they  are  seated 
is  composed  almost  entirely  of 
fine  elastic  fibres,  which  form  an 
intricate  interlacement  about  the 
cells,  and  in  their  general  charac- 
ters are  allied  to  the  yellow 
variety  of  fibrous  tissue  :  a  small 
and  variable  quantity  of  hyaline 
intercellular  substance  is  also 
usually  present. 

A  variety  of  elastic  cartilage, 
sometimes  called  cellular,  may  be 
obtained  from  the  external  ear  of  rats,  mice,  or  other  small  mam- 
mals. It  is  composed  almost  entirely  of  cells  (hence  the  name), 
which  are  packed  very  closely,  with  little  or  no  matrix.  When 
present  the  matrix  consists  of  very  fine  fibres,  which  twine  about 
the  cells  in  various  directions  and  enclose  them  in  a  kind  of 
network. 


Fig.  41. — Section  of  the  epiglottis.    (Baly«) 


Fig.  42.—  Transverse  section  through  the  intervertebral  cartilage  of  tail  of  mouse,  showing 
lamelhe  of  fibrous  tissue  with  cartilage  cells  arranged  in  rows  between  them.  The 
cells  are  seen  in  profile,  and  being  flattened,  appear  staff -shaped.  Each  cell  lies  in  a 
capsule,     x  350.    (Klein  and  Noble  Smith.) 

3.  White  Fibro-Cartilage. 

Distribution. — The  different  situations  in  which  white  fibro-carti- 
lage  is  found  have  given  rise  to  the  following  classification  : — 

1.  Inter-articular  fibro-cartilage,  e.g.,  the  semilunar  cartilages  of 
the  knee-joint. 


50  STRUCTURE    OF    ELEMENTARY    TISSUES.      [chap. 

2.  Circumferential  or  marginal,  as  on  the  edges  of  the  aceta- 
bulum and  glenoid  cavity. 

3.  Connecting,  e.g.,  the  inter-vertebral  fibro-cartilages. 

4.  In  the  sheaths  of  tendons,  and  sometimes  in  their  substance. 
In  the  latter  situation,  the  nodule  of  fibro-cartilage  is  called  a 
sesamoid  fibro-cartilage,  of  which  a  specimen  may  be  found  in  the 
tendon  of  the  tibialis  posticus,  in  the  sole  of  the  foot,  and  usually 
in  the  neighbouring  tendon  of  the  peroneus  longus. 

Structure. — White  fibro-cartilage  (fig.  43),  which  is  much  more 
widely  distributed  throughout  the  body  than  the  foregoing  kind, 

is   composed,  like   it,  of  cells 


'; f! """ "| 


and  a  matrix ;  the  latter,  how- 
ever, being  made  up  almost 
entirely  of  fibres  closely  re- 
sembling those  of  white  fibrous 
tissue. 

In  this  kind  of  fibro-cartilage 
it  is  not  unusual  to  find  a  great 
part  of  its  mass  composed 
almost  exclusively  of  fibres,  and 
deriving  the  name  of  cartilage 
only  from  the  fact  that  in  an- 

Fig.  tf.-White  fibro-cartilage  from  an  inter-         Other  portion,  COlltillUOUS  with 
vertebral  ligament.     (Klein  and  Noble        ^  cartikgc  ceUg  may  be  prett y 

freely  distributed. 

Functions  of  Cartilage. — Cartilage  not  only  represents  in 
the  foetus  the  bones  which  are  to  be  formed  (temporary  cartilage), 
but  also  offers  a  firm,  but  more  or  less  yielding,  framework  for 
certain  parts  in  the  developed  body,  possessing  at  the  same  time 
strength  and  elasticity.  It  maintains  the  shape  of  tubes  as 
in  the  larynx  and  trachea.  It  affords  attachment  to  muscles 
and  ligaments ;  it  binds  bones  together,  yet  allows  a  certain 
degree  of  movement,  as  between  the  vertebrae ;  it  forms  a 
firm  framework  and  protection,  yet  without  undue  stiffness  or 
weight,  as  in  the  pinna,  larynx,  and  chest  walls;  it  deepens  joint 
cavities,  as  in  the  acetabulum,  without  unduly  restricting  the 
movements  of  the  bones. 

Development  of  Cartilage.— Cartilage  is  developed  out  of  an 
embryonal  tissue,  consisting  of  cells  with  a  very  sma.ll  quantity  of 


chap,  in.]  BONE.  5 1 

intercellular  substance:  the  cells  multiply  by  fission  within  the 
cell-capsules  (fig.  6);  while  the  capsule  of  the  parent  cell  becomes 
gradually  fused  with  the  surrounding  intercellular  substance.  A 
repetition  of  this  process  in  the  young  cells  causes  a  rapid  growth 
of  the  cartilage  bythe  multiplication  of  its  cellular  elements  and 
corresponding  increase  in  its  matrix. 


III.  Bone. 

Chemical  Composition. — Bone  is  composed  of  earthy  and 
animal  matter  in  the  proportion  of  about  67  per  cent,  of  the 
former  to  33  per  cent,  of  the  latter.  The  earthy  matter  is  com- 
posed chiefly  of  calcium  phosphate,  but  besides  there  is  a  small 
quantity  (about  11  of  the  67  per  cent.)  of  calcium  carbonate  and 
fluoride,  and  magnesium  phosphate. 

The  animal  matter  is  resolved  into  gelatin  by  boiling. 

The  earthy  and  animal  constituents  of  bone  are  so  intimately 
blended  and  incorporated  the  one  with  the  other,  that  it  is  only 
1  > y  chemical  action,  as,  for  instance,  by  heat  in  one  case  and  by  the 
action  of  acids  in  another,  that  they  can  be  separated.  Their 
close  union,  too,  is  further  shown  by  the  fact  that  when  by  acids 
the  earthy  matter  is  dissolved  out,  or,  on  the  other  hand,  when  the 
animal  part  is  burnt  out,  the  shape  of  the  bone  is  alike  preserved. 

The  proportion  between  these  two  constituents  of  bone  varies  in 
different  bones  in  the  same  individual,  and  in  the  same  bone  at 
different  ages. 

Structure. — To  the  naked  eye  there  appear  two  kinds  of  struc- 
ture in  different  bones,  and  in  different  parts  of  the  same  bone, 
namely,  the  dense  or  compact,  and  the  spongy  or  cancellous  tissue. 

Thus,  in  making  a  longitudinal  section  of  a  long  bone,  as  the 
humerus  or  femur,  the  articular  extremities  are  found  capped  on 
their  surface  by  a  thin  shell  of  compact  bone,  while  their  interior 
is  made  up  of  the  spongy  or  cancellous  tissue.  The  shaft,  on  the 
1  >t her  hand,  is  formed  almost  entirely  of  a  thick  layer  of  the  compact 
bone,  and  this  surrounds  a  central  canal,  the  medullary  cavity — so 
called  from  its  containing  the  medulla  or  marrow. 

In  the  flat  bones,  as  the  parietal  bone  or  the  scapula,  one  layer 
of  the  cancellous  structure  lies  between  two  layers  of  the  compact 
tissue,  and  in  the  short  and  irregular  bones,  as  those  of  the  carp** 

E  2 


52 


STRUCTURE    OF    ELEMENTARY    TISSUES.      [chap.  hi. 


and  tarsus,  the  cancellous  tissue  alone  fills  the  interior,  while  a 
thin  shell  of  compact  bone  forms  the  outside. 

Marrow. — There  are  two  distinct  varieties  of  marrow — the  red 
and  yelloiv. 

Red  marrow  is  that  variety  which  occupies  the  spaces  in  the 
cancellous  tissue  ;  it  is  highly  vascular,  and  thus  maintains  the 


Fig.  44. — Cells  of  the  red  marrow  of  the  guinea  pig,  highly  magnified.  0,  a  large  cell,  the 
nucleus  of  which  appears  to  be  partly  divided  into  three  by  constrictions  ;  b,  a  cell,  the 
nucleus  of  which  shows  an  appearance  of  being  constricted  into  a  number  of  smaller 
nuclei ;  c,  a  so-called  giant  cell,  or  myeloplaxe,  with  many  nuclei ;  d,  a  smaller  myelo- 
plaxe,  with  three  nuclei ;  e — i,  proper  cells  of  the  marrow.     (E.  A.  Schafer.) 


nutrition  of  the  spongy  bone,  the  interstices  of  which  it  fills.  It 
contains  a  few  fat-cells  and  a  large  number  of  marrow-cells,  many 
of  which  are  undistinguishable  from  lymphoid  corpuscles,  and  has 
for  a  basis  a  small  amount  of  fibrous  tissue.  Among  the  cells  are 
some  nucleated  cells  of  very  much  the  same  tint  as  coloured 
blood-corpuscles.  There  are  also  a  few  large  cells  with  many 
nuclei,  termed  "  giant-cells  "  (myeloplaxes),  which  are  derived  from 
over-growth  of  the  ordinary  marrow-cells  (fig.  44). 

Yelloiv  marrow  fills  the  medullary  cavity  of  long  bones,  and 
consists  chiefly  of  fat-cells  with  numerous  blood-vessels  ;  many  of 
its  cells  also  are  in  every  respect  similar  to  lymphoid  corpuscles. 

From  these  marrow-cells,  especially  those  of  the  red  marrow,  are 
derived,  as  we  shall  presently  show,  large  quantities  of  red  blood- 
corpuscles. 

Periosteum  and  Nutrient  Blood-vessels. — The  surfaces  of 
bones,  except  the  part  covered  with  articular  cartilage,  are 
clothed  by  a  tough,  fibrous  membrane,  the  periosteum ;  and  it 
is   from   the   blood-vessels   which  are  distributed   in   this  mem- 


(HAP.  III.] 


STRUCTURE    OF    BONE. 


53 


brane,  that  the  1  tones,  especially  their  more  compact  tissue,  are 
in  great  part  supplied  with  nourishment, — minute  branches  from 
the  periosteal  vessels  entering  the  little  foramina  on  the  surface  of 
the  hone,  and  finding  their  way  to  the  Haversian  canals,  to  be 
immediately  described.  The  long  bones  are  supplied  also  by  a 
proper  nutrient  artery  which,  entering  at  some  part  of  the  shaft 
so  as  to  reach  the  medullary  canal,  breaks  up  into  branches  for 
the  supply  of  the  marrow,  from  which  again  small  vessels  are  distri- 
buted to  the  interior  of  the  bone.  Other  small  blood-vessels  pierce 
the  articular  extremities  for  the  supply  of  the  cancellous  tissue. 

Microscopic  Structure  of  Bone. — Notwithstanding  the  dif- 
ferences of  arrangement  just  mentioned,  the  structure  of  all  bone 
is  found  under  the  microscope  to  be  essentially  the  same. 

Examined  with  a  rather  high  power  its  substance  is  found  to 
contain    a    multitude   of    little    irregular   spaces,    approximately 


Fig.  45. — Transverse  section  of  compact  bony  tissue  (of  humerus).  Three  of  the  Haversian 
canals  are  seen,  with  their  concentric  rings ;  also  the  corpuscles  or  lacuna?,  with  the 
canaliculi  extending  from  them  across  the  direction  of  the  lamella?.  The  Haversian 
apertures  had  got  filled  with  debris  in  grinding  down  the  section,  and  therefore  appear 
Muck  in  the  figure,  which  represents  the  object  as  viewed  with  transmitted  light.  The 
Haversian  systems  are  so  closely  packed  in  this  section,  that  scarcely  any  interstitial 
lamellae  are  visible,    x  150.    (Sharpey.) 

fusiform  in  shape,  called  lacunae  f  with  very  minute  canals  or 
canaliculi,  as  they  are  termed,  leading  from  them,  and  anasto- 
mosing with  similar  little  prolongations  from  other  lacunae  (fig.  45). 


54 


STRUCTURE    OF    ELEMENTARY    TISSUES.       [chap.  hi. 


In  very  thin  layers  of  bone,  no  other  canals  than  these  may  be 
visible ;  but  on  making  a  transverse  section  of  the  compact  tissue 
as  of  a  long  bone,  e.g.,  the  humerus  or  ulna,  the  arrangement 
shown  in  fig.  45,  can  be  seen. 

The  bone  seems  mapped  out  into  small  circular  districts,  at  or 
about  the  centre  of  each  of  which  is  a  hole,  and  around  this  an 
appearance  as  of  concentric  layers — the  lacuwe  and  canaliculi 
following  the  same  concentric  plan  of  distribution  around  the 
small  hole  in  the  centre,  with  which,  indeed,  they  communicate. 

On  making  a  longitudinal  section,  the  central  holes  are  found 
to   be    simply  the    cut    extremities  of  small    canals    which    run 


mm 

mm 

mm 

mm 


m 


mm  m 

pi  m 


ml*  Am 

MM 


Fig.  46.— Longitudinal  section  of  human  ulna,  showing  Haversian  canal,  lacume,  and 

canaliculi.     (Eollett.) 

lengthwise  through  the  bone,  anastomosing  with  each  other  by 
lateral  branches  (fig.  46),  and  are  called  Haversian  canals,  after 
the  name  of  the  physician,  Clopton  Havers,  who  first  accurately 
described  them.  The  Haversian  canals,  the  average  diameter  of 
which  is  T^y  of  an  inch,  contain  blood-vessels,  and  by  means  of 
them  blood  is  conveyed  to  all,  even  the  densest  parts  of  the  bone  ; 
the  minute  canaliculi  and  lacunae  absorbing  nutrient  matter  from 
the  Haversian  blood-vessels,  and  conveying  it  still  more  intimately 
to  the  very  substance  of  the  bone  which  they  traverse. 


<   MAI'.    III.] 


STRUCTURE  OF    BONE, 


55 


The  blood-vessels  enter  the  Haversian  canals  both  from  without, 
by  traversing  the  Bmall  holes  which  exist  on  the  surface  of  all 
bones  beneath  the  periosteum,  and  from  within  by  means  of  Bmall 
channels  which  extend  from  the  medullary  cavity,  or  from  the 
cancellous  tissue.  The  arteries  and  veins  usually  occupy  separate 
canals,  and  the  veins,  which  are  the  larger,  often  present,  at 
irregular  intervals,  small  pouch-like  dilatations. 

The  lacunae  are  occupied  by  branched  cells  (hone-cells,  or  bone- 
oorpuscles)  (fig.  47),  which 
very  closely  resemble  the 
ordinary  branched  connec- 
tive-tissue corpuscles ;  each 
of  these  little  masses  of 
protoplasm  ministering  to 
the  nutrition  of  the  bone 
immediately  surrounding  it, 
and  one  lacunar  corpuscle 
communicating  with  an- 
other, and  with  its  sur- 
rounding district,  and  with 
the  blood-vessels  of  the 
Haversian  canals,  by  means 
of  the  minute  streams  of 
fluid  nutrient  matter  which 
occupy  the  canaliculi. 

It  will  be  seen  from  the 
above  description  that  bone  is  essentially  connective-tissue  impreg- 
nated with  lime  salts  :  it  bears  a  very  close  resemblance  to  what 
may  be  termed  typical  connective-tissue  such  as  the  substance  of 
the  cornea.  The  bone-corpuscles  with  their  processes,  occupying 
the  lacunae  and  canaliculi,  correspond  exactly  to  the  cornea- 
corpuscles  lying  in  branched  spaees ;  while  the  finely  fibrillated 
structure  of  the  bone-lamella),  to  be  presently  described,  resembles 
the  fibrillated  substance  of  the  cornea  in  which  the  branching 
spaces  lie. 

Lamellae  of  Compact  Bone.— In  the  shaft  of  a  long  bone 
three  distinct  sets  of  lamella}  can  be  clearly  recognised. 

(1.)  General  or  fundamental  lamella);  which  are  most  easily 
traceable  just  beneath  the  periosteum,  and  around  the  medullary 


Fisr.  47. — Bone  corpuscles  with  their  process.  - 
seen  in  a  thin  section  of  human  bone.    (Kollett.) 


STRUCTURE    OF    ELEMENTARY    TISSUES.      [chap,  ill' 


cavity,  forming  around  the  latter  a  series  of  concentric  rings.     At 
a  little  distance  from  the  medullary  and  periosteal  surfaces  (in  the 

deeper  portions  of  the  bone)  they  are  more 
or  less  interrupted  by 

(2.)  Special  or  Haversian  lamellae,  which 
are  concentrically  arranged  around  the 
Haversian  canals  to  the  number  of  six  to 
eighteen  around  each. 

(3.)  Interstitial  lamellae,  which  connect 
the  systems  of  Haversian  lamellae,  filling 
the  spaces  between  them,  and  conse- 
quently attaining  their  greatest  develop- 
ment where  the  Haversian  systems  are 
few,  and  vice  verso. 

The  ultimate  structure  of  the  lamella: 
appears  to  be  reticular.  If  a  thin  film  be 
peeled  off  the  surface  of  a  bone,  from  which 
the  earthy  matter  has  been  removed  by 
acid,  and  examined  with  a  high  power  of 
the  microscope,  it  will  be  found  composed  of  a  finely  reticular 
structure,   formed  apparently  of  very  slender  fibres  decussating 


f'///v'-'- .-■>"■'     '  v'. 
{';,' ■'-  :"  ■'.'■'",V>r.v 

Fig.  48. — Thin  layer  peeled  off 
from  a  softened  bone.  This 
figure,  'which  is  intended  to 
represent  the  reticular 
structure  of  a  lamella,  gives 
a  better  idea  of  the  object 
when  held  rather  farther 
off  than  usual  from  the 
eye.     x  400.     (Sharper.) 


ST*  Or- 


Fig.  49. — Lamella;  torn  off  from  a  decalcified  human  parietal  bone  at  some  depth  from 
the  surface,  a,  a  lamella,  showing  reticular  fibres  ;  b,  b,  darker  part,  where  several 
lamellae  are  superposed  ;  c,  perforating  fibres.  Apertures  through  which  perforating 
fibres  had  passed,  are  seen  especially  in  the  lower  pail,  a,  a,  of  the  figure.  (Allen 
Thomson.) 


chap.ih.]  DEVELOPMENT    OF    BONE.  57 

liquely,  but  1  Ing  at  the  points  of  intersection,  as  if  hi 

the   61  I   rather   than    woven    together    (fig.    48). 

-    irpey.) 

In  many  places  these  reticular  lamellse  are  perforated  by  taper- 
ing fibres  (Claviculi  of  Gagliardi),  resembling  in  character  the 
ordinary  white  or  rarely  the  elastic  fibrous  tissue,  which  bolt  the 
neighbouring  lamellse  together,  and  may  be  drawn  out  when  the 
latter  are  torn  asunder  (fig.  49).  These  perforating  fibres  origin  * 
60m  ingrowing  pn  -  3  of  the  periosteum,  and  in  the  adult  still 
retain  their  connection  with  it. 

Development  of  Bone. — From  the  point  of  view  of  their 
development,  all  bones  may  be  subdivided  into  two  classes. 

(a.)  Those  which  are   ossified    directly  in  membrane,   e.g..  the 

-  forming  the  vault  of  the  skull,  parietal,  frontal. 

i      3       bos    form,  previous  :      ssification,  is  laid  down  in 
hyali  tilage,  e.g.,  humerus,  femur. 

The    pn      —   of  development,   pure    and    simple,   may 
studied  in  bones  which  are  not  preceded  by  cartilage — ;;  membrane- 

-  "  (e.g.,  parietal)  :  and  without  a  knowledge  of  this 

— irlcation  in  membrane),  it  is  impossible  to  understand  the  much 
more  complex  -  ri  a  f  changes  through  which  such  a  structure  a 
the  cartilaginous  femur  of  the  foetus  passes  in  its  transformation 
into  the  bony  femur  of  the  adult  (ossification  in  cartilage). 

Ossification  in  Membrane. — The    membrane  or  periosteum 
from  which   such  a  bone  as  the  parietal  is  developed  consists  of 
two  layers — an  external  fibrous,  and  an  internal  cellular  or  osL 
tic 
The  external  one  consists     f  ordinary  connective-tissue,  being 
composed  of  layers   of  fibrous  tissue  with  branched   connective- 
sue  corpuscles  here  and  there  between  the  bundles  of  fibi 
The  internal  layer  consists     :  a  network  of  tine  fibrils  with  a  lai  _ 
number  of  nucleated  cells,  some  of  which  are  oval,  others  drawn 
out  into  a  long  branched  pi       as,  and  others  branched  :  it  is  more 
richly  supplied  with  capillaries  than  the  outer  layer.      The  rela- 
tively large  number  of  its  cellular  elements,  their  variability  in 

3  and  -hape,  together  with  the  abundance  of  its  blood-? 
clearly  mark  it       -     -  the  portion  of  the  periosteum  which  is  im- 
mediately concerned  in  the  formation  of  bone. 

In  such  a  bone  as  the  parietal,  the  deposition  of  bony  matter. 


53. 


STRUCTURE    OF    ELEMENTARY    TISSUES.       [chap.  hi. 


which  is  preceded  by  increased  vascularity,  takes  place  in  radiat- 
ing spiculse,  starting  from  a  "  centre  of  ossification,"  and  shooting- 
out  in  all  directions  towards  the  periphery  ;  while  the  bone  in- 
creases in  thickness  by  the  deposition  of  successive  layers  beneath 
the  periosteum.  The  finely  fibrillar  network  of  the  deeper  or 
osteogenetic  layer  of  the  periosteum  becomes  transformed  into  bone- 
matrix  (the  minute  structure  of  which  has  been  already  (p.  55) 
described  as  reticular),  and  its  cells  into  bone-corpuscles.  On  the 
young  bony  trabecule  thus  formed,  fresh  layers  of  cells  (osteo- 
blasts)  from  the  osteogenetic  layer  are   developed  side  by  side, 


Fig.  so.—  QsteoLhisf.*:  from  the  parietal  bone  of  a  human  embryo,  thirteen  weeks  old.  a, 
bony  septa  with  the  cells  of  the  lacuna? ;  h,  layers  of  osteoblasts  ;  c,  the  latter  in  tran- 
sition to  bone  corpuscles.    Highly  magnified.     (Gegenbaur.) 


lining  the  irregular  spaces  like  an  epithelium  (fig.  50,  L).  Lime- 
salts  are  deposited  in  the  circumferential  part  of  each  osteoblast, 
and  thus  a  ring  of  osteoblasts  gives  rise  to  a  ring  of  bone  with  the 
remaining  uncalcified  portions  of  the  osteoblasts  imbedded  in  it  as 
bone-corpuscles  (fig.  50). 

Thus,  the  primitive  spongy  bone  is  formed,  whose  irregular 
branching  spaces  are  occupied  by  processes  from  the  osteogenetic 
layer  of  the  periosteum  with  numerous  blood-vessels  and  osteo- 
blasts. Portions  of  this  primitive  spongy  bone  are  re-absorbed ; 
the  osteoblasts  being  arranged  in  concentric  successive  layers  and 
thus  giving  rise  to  concentric  Haversian  lamella)  of  bone,  until  the 
irregular  space  in  the  centre  is  reduced  to  a  well-formed  Haversian 
canal,  the  portions  of  the  primitive  spongy  bone  between  the  Haver- 
sian systems  remaining  as  interstitial  or  ground-lamellaB  (p.    56). 


I  HAP.  m. J 


DEVELOPMENT    OF    BONE, 


59 


The  bulk  of  the  primitive  spongy  bone  is  thus  gradually  converted 
into  compact  bony-tissue  with  Haversian  canals.  Those  portions 
of  the  in-growths  from  the  deeper  layer  of  the  periosteum  which 
are  not  converted  into  bone  remain  in  the  spaces  of  the  cancellous 
tissue  as  the  red  marrow, 

Ossification  in  Cartilage. — Under  this  heading,  taking  the 
femur  as  a  typical  example,  we  may  consider  the  process  by  which 
the  solid  cartilaginous  rod 
which  represents  it  in  the 
foetus  is  converted  into  the 
hollow  cylinder  of  compact 
bone  with  expanded  ends 
of  cancellous  tissue  which 
forms  the  adult  femur ; 
bearing  in  mind  the  fact  that 
this  foetal  cartilaginous  femur 
is  many  times  smaller  than 
the  medullary  cavity  even  of 
the  shaft  of  the  mature 
bone,  and,  therefore,  that 
not  a  trace  of  the  original 
cartilage  can  be  present  in 
the  femur  of  the  adult.  Its 
purpose  is  indeed  purely  tem- 
porary ;  and,  after  its  calci- 
fication, it  is  gradually  and 
entirely  re-absorbed  as  will  be 
presently  explained. 

The  cartilaginous  rod  which 
forms  the  foetal  femur  is 
sheathed  in  a  membrane 
termed  the  perichondrium, 
which  so  far  resembles  the 
periosteum    described    above, 

that  it  consists  of  two  layers,  in  the  deeper  one  of  which  spheroidal 
cells  predominate  and  blood-vessels  abound,  while  the  outer  layer 
consists  mainly  of  fusiform  cells  which  are  in  the  mature  tissue 
gradually  transformed  into  fibres.  Thus,  the  differences  between 
the  foetal  perichondrium  and  the  periosteum  of  the  adult  are  such 


CH 


Fig\  51. — From  a  transversi  section  through  part 
of  foetal  jaw  near  the  extreme  periosteum,  in 
the  state  of  spongy  bone,  p,  fibrous  layer  of 
periosteum ;  b,  osteogenetic  layer  of  perios- 
teum ;  o,  osteoblasts  ;  c,  osseous  substance, 
containing  many  bone  corpuscles.     X  300. 

(Schofiekl.) 


6o 


STRUCTURE    OF    ELEMENTARY    TISSUES.      [chap.  in. 


as    usually   exist    between  the   embryonic  and  mature  forms  of 
connective-tissue. 

Between  the  hyaline  cartilage  of  which  the  foetal  femur  consists 


r  4- 


pj0.>  ^2# — Ossifying  cartilage  showing  loops  of  blood-vessels. 


and  the  bony  tissue  forming  the  adult  femur,  two  intermediate 
stages  exist — viz.,  calcined  cartilage,  and  embryonic  spongy  bone. 
These  tissues,   which  successively  occupy  the  place  of  the  foetal 


CHAP,  III. J 


DEVELOPMENT    OF    BONE. 


61 


cartilage,  are  in  bu<  i   entirely  re-absorbed,  and  their  place 

taken  by  true  bone. 

The  process  by  which  the  cartilaginous  is  transformed  into  the 
bony  femur  may  be  divided  for  the  sake  of  clearness  into  the 
following  six  Btages  : — 

Stage   1.— Vascularisation    of    the    Cartilage.—  Proc 
from   the   oeteogenetic   <>r   cellular  layer  of  the   perichondrium 
containing  blood-vessels  grow  into  the  substance  of  the  cartilage 


from  the  humerus  of  a  fetal  sheep. 
I  ified  trabecule  are  seen  extending  between  the  columns  of  cartilage  cells,    c,  cai- 
tilage  cells,     x  i  p.     v^harpey.) 

much  as  ivy  insinuates  itself  into  the  cracks  and  crevices  of  a 
wall.  Thus  the  substance  of  the  cartilage,  which  previously 
contained  no  vessels,  is  traversed  by  a  number  of  branched 
anastomosing  channels  formed  bv  the  enlargement  and  coalescence 
of  the  spaces  in  which  the  cartilage-cells  lie,  and  containing  loops 
of  blood-vessels  (fig.  52)  and  spheroidal-cells  which  will  become 
osteobh- 


62 


STRUCTURE    OF    ELEMENTARY    TISSUES.       [chap.  hi. 


Stage  2.— Calcification  of  Cartilaginous  Matrix. — Lime- 
salts  are  next  deposited  in  the  form  of  fine  granules  in  the  hyaline 
matrix  of  the  cartilage,  which  thus  becomes  gradually  transformed 
into  a  number  of  calcified  trabecule  (fig.  54,  5),  forming  alveolar 
spaces  (primary  areola-)  containing  cartilage  cells.     By  the  absorp- 


Yis.  54. — T,      -      •    -  ofaportii  f,  showing — i,  fibrous 

layer  of  periosteum;  2,  oncogenetic  layer  of  ditto;  3,  periosteal  borne;  4,  cartflage 
with  matrix  gradually  becoming  calcified,  as  at  5,  with  cells  in  primary  areola? :  beyond 
5  the  calcified  matrix 'is  being  entirely  replaced  by  spongy  bone,  x  200.   ( V.  D.  Harris.) 

tion  of  some  of  the  trabecule  larger  spaces  arise,  which  contain 
cartilage-cells  for  a  very  Bhort  time  only,  their  places  being  taken 
by  the  so-called  osteogenetic  layer  of  the  perichondrium  (before 
referred  to  in  Stage  1)  which  constitutes  the  primary  marrow.  The 
cartilage-cells,  gradually  enlarging,  become  more  transparent  and 
finally  undergo  disintegration. 

Stage    3.—  Substitution    of    Embryonic    Spongy    Bone 
for  Cartilage. — The  cells  of  the  primary  marrow  arrange  them- 


OHAP.   in.  | 


DEVELOPMENT    OF    BONE. 


63 


a  — 

0&    C 


?*;: 


^^ff^ 


selves  as  a  continuous  layer  like  epithelium  on  the  calcified 
trabecule  and  deposit  a  layer  of  bone,  which  ensheathes  the  calci- 
fied trabecules :  these  calci- 
fied trabecule?,  encased  in 
their  sheaths  of  young  bone, 
become  gradually  absorbed, 
so  that  finally  Ave  have  tra- 
becule composed  entirely 
of  spongy  bone,  all  trace 
of  the  original  calcified  car- 
tilage having  disappeared. 
It  is  probable  that  the  large 
multinucleated  giant-cells 
termed  "osteoclasts"  b}^ 
Kolliker,  which  are  derived 
from  the  osteoblasts  by  the 
multiplication  of  their  nu- 
clei, are  the  agents  by 
which  the  absorption  of 
calcified  cartilage,  and  sub- 
sequently of  embryonic 
spongy  bone,  is  carried  on 

(fig.  55,  g).     At  any  rate  they  are  almost  always  found  wherever 
absorption  is  in  progress. 

Stages  2  and  3  are  precisely  similar  to  what  goes  on  in  the 
growing  shaft  of  a  bone  which  is  increasing  in  length  by  the 
advance  of  the  process  of  ossification  into  the  intermediary  carti- 
between  the  diaphysis  and  epiphysis.  In  this  case  the 
cartilage-cells  become  flattened  and,  multiplying  by  division,  are 
grouped  into  regular  columns  at  right  angles  to  the  plane  of 
calcification,  while  the  process  of  calcification  extends  into  the 
hyaline  matrix  between  them  (figs.  52  and  53). 

Stage  4.— Substitution  of  Periosteal  Bone  for  the 
Primary  Embryonic  Spongy*  Bone.— The  embryonic  spongy 
bone,  formed  as  above  described,  is  simply  a  temporary  tissue 
occupying  the  place  of  the  foetal  rod  of  cartilage,  once  representing 
the  femur;  and  the  stages  1,  2,  and  3  show  the  successive  changes 
which  occur  at  the  centre  of  the  shaft.  Periosteal  bone  is  now 
deposited  in  successive  layers  beneath  the  periosteum,  i.e.,  at  tlte 


Fig.  55. — A  small  isolated  mass  of  bone  next  the 
periosteum  of  the  lower  ja"W  of  human  fuetus. 
a,  osteogenetic  layer  of  periosteum.  G,  mul- 
tinuclear  giant  cells,  the  one  on  the  left  acting 
here  probably  like  an  osteoclast.  Above  c, 
the  osteoblasts  are  seen  to  become  surrounded 
by  an  osseous  matrix.  (Klein  and  Noble 
Smith.) 


64 


STRUCTURE    OF    ELEMENTARY    TISSUES.       [chap.  hi. 


circumference  of  the  shaft,  exactly  as  described  in  the  section  on 
"  ossification  in  membrane,"  and  thus  a  casing  of  periosteal  bone 
is  formed  around  the  embryonic  endochondral  spongy  bone  :  this 


Fig.  56.  —  Transverse  section  through  the  tibia  of  a  foetal  kitten  semi-diagrammatic. 
x  60.  P,  Periosteum.  O,  osteogenetic  layer  of  the  periosteum,  showing  the  osteo- 
blasts arranged  side  by  side,  represented  as  pear-shaped  black  dots  on  the  surface  of 
the  newly-formed  bone.  B,  the  periosteal  bone  deposited  in  successive  layers  beneath 
the  periosteum  and  ensheathing  E,  the  spongy  endochondral  bone  ;  represented  as 
more  deeply  shaded.  Within  the  trabecule?  of  endochondral  spongy  bone  are  seen 
the  remains  of  the  calcined  cartilage  trabecule  represented  as  dark  wavy  lines.  C, 
the  medulla,  with  V,  T,  veins.  In  the  lower  half  of  the  figure  the  endochondral 
spongy  bone  has  been  completely  absorbed.     (Klein  and  Noble  Smith.) 


casing  is  thickest  at  the  centre,  where  it  is  first  formed,  and  thins 
out  towards  each  end  of  the  shaft.  The  embryonic  spongy  bone 
is  absorbed,   its  trabecule  becoming  gradually  thinned  and  its 


CHAP,   HI.] 


DEVELOPMENT    OK    BONE. 


65 


meshes  enlarging,  and  finally  coalescing  into  one  greal    cavity — 
the  medullary  cavity  of  the  shaft. 

Stage  5.— Absorption  of  the  Inner  Layers  of  the  Perios- 
teal Bone. — The  absorption  of  the  endochondral  spongy  l>onc  is 
now  complete,  and  the  medullary  cavity  is  bounded  by  periosteal 
bone:  the  inner  layers  of  this  periosteal  bone  are  next  absorbed, 
and  the  medullary  cavity  is  thereby  enlarged,  while  the  deposition 
Of  bone  beneath  the  periosteum  continues  as  before.  The  first  - 
formed  periosteal  bone  is  spongy  in  character. 

Stage  6.— Formation  of  Compact  Bone. — The  transforma- 
tion of  spongy  periosteal  bone  into  compact  bone  is  effected  in  a 
manner  exactly  similar 
to  that  which  has  been 
described  in  connection 
with  ossification  in 
membrane  (p.  58).  The 
Irregularities  in  the 
walls  of  the  areolae  in 
the  spongy  hone  are  ab- 
sorbed, while  the  osteo- 
blasts which  line  them 
are  developed  in  concen- 
tric layers,  each  layer  in 
turn  becoming  ossified 
till  the  comparatively 
large  space  in  the  centre 
is  reduced  to  a  well- 
formed  Haversian  canal 
(fig.  57).  When  once 
formed,  bony  tissue  gr<  >  ws 
to  some  extent  intersti- 
tially,  as  is  evidenced 
by  the  fact  that  the  la- 
cuna; are  rather  further 
apart  in  fully-formed 
than  in  young  bone. 

From  the  foregoing  description  of  the  development  of  bone,  it 

will  be  seen  that  the  common  terms  "ossification  in  cartilage  "  and 

sification  in  membrane  "  are  apt  to  mislead,  since  they  seem  to 


Fig.  57.  —  Transverse  section  of  femur  of  a  human 
embryo  about  eleven  weeks  old.  a,  rudimen- 
tary Haversian  canal  in  cross  section ;  b,  in  lon- 
gitudinal section  ;  r,  osteoblasts  ;  d,  newly  formed 
osseous  substance  of  a  lighter  colour;  e,  that  of 
greater  age  ;  /,  lacunto  with  their  cells  ;  g,  a  cell 
still  united  to  an  osteoblast.     (Frey.) 


66  STRUCTURE    OF   ELEMENTARY    TISSUES.        [chap.  hi. 

imply  two  processes  radically  distinct.  The  process  of  ossification, 
nowever,  is  in  all  cases  one  and  the  same,  all  true  bony  tissue  being- 
formed  from  membrane  (perichondrium  or  periosteum) ;  but  in  the 
development  of  such  a  bone  as  the  femur,  which  may  be  taken  as  the 
type  of  so-called  "  ossification  in  cartilage,"  lime-salts  are  deposited 
in  the  cartilage,  and  this  calcified  cartilage  is  gradually  and  entirely 
re-absorbed,  being  ultimately  replaced  by  bone  formed  from  the 
periosteum,  till  in  the  adult  structure  nothing  but  true  bone  is 
left.  Thus,  in  the  process  of  "  ossification  in  cartilage,"  calcifica- 
tion of  the  cartilaginous  matrix  precedes  the  real  formation  of 
bone.  AVe  must,  therefore,  clearly  distinguish  between  calcifica- 
tion and  ossification.  The  former  is  simply  the  infiltration  of 
an  animal  tissue  with  lime-salts,  and  is,  therefore,  a  change  of 
chemical  composition  rather  than  of  structure  ;  while  ossification 
is  the  formation  of  true  bone — a  tissue  more  complex  and  more 
highly  organized  than  that  from  which  it  is  derived. 

Centres  of  Ossification. — In  all  bones  ossification  commences 
atone  or  more  points,  termed  "centres  of  ossification."  The  long- 
bones,  eg.,  femur,  humerus,  &c,  have  at  least  three  such  points 
— one  for  the  ossification  of  the  shaft  or  dia/physis,  and  one  for 
each  articular  extremity  or  epiphysis.  Besides  these  three  primary 
centres  which  are  always  present  in  long  bones,  various  secondary 
centres  may  be  superadded  for  the  ossification  of  different  processes. 

Growth  of  Bone. — Bones  increase  in  length  by  the  advance 
of  the  process  of  ossification  into  the  cartilage  intermediate 
between  the  diaphysis  and  epiphysis.  The  increase  in  length 
indeed  is  clue  entirely  to  growth  at  the  two  ends  of  the  shaft. 
This  is  proved  by  inserting  two  pins  into  the  shaft  of  a  growing- 
bone  :  after  some  time  their  distance  apart  will  be  found  to  be  un- 
altered though  the  bone  has  gradually  increased  in  length,  the 
growth  having  taken  place  beyond  and  not  between  them.  If  now 
one  pin  be  placed  in  the  shaft,  and  the  other  in  the  epiphysis,  of  a 
growing  bone,  their  distance  apart  will  increase  as  the  bone  grows 
in  length. 

Thus  it  is  that  if  the  epiphyses  with  the  intermediate  cartilage 
be  removed  from  a  young  bone,  growth  in  length  is  no  longer  pos- 
sible ;  while  the  natural  termination  of  growth  of  a  bone  in  length 
takes  place  when  the  epiphyses  become  united  in  bony  continuity 
with  the  shaft. 


DEAF.   Hi. J 


TEE!  I!. 


6? 


[ncrease  in  thickneu  in  the  shaft  of  a  long  bone,  occurs  by  the 
deposition  of  successive  layers  beneath  the  periosteum. 

[fa  thin  metal  plate  be  inserted  beneath  the  periosteum  of  a 
growing  bone,  it  will  soon  l>e  covered  by  osseous  deposit,  but  if  it 
he  put  between  the  fibrous  and  osteogenetic  layers,  it  will  never 
become  enveloped  in  bone,  for  all  the  bone  is  formed  beneath  the 
latter. 

Other  varieties  of  connective  tissue  may  become  ossified,  e.g.,  the  tendons 
in  some  birds. 

Functions  of  Bones. — Bones  form  the  framework  of  the  body; 

for  this  they  are  fitted  by  their  hardness  and  solidity  together  with 
their  comparative  lightness  ;  they  serve  both  to  protect  internal 
organs  in  the  trunk  and  skull,  and  as  levers  worked  by  muscles 
in  the  limbs;  notwithstanding  their  hardness  they  possess  a 
considerable  degree  of  elasticity,  which  often  saves  them  from 
fractures. 

Teeth. 

The  principal  part  of  a  tooth,  viz.,  dentine,  is  called  by  some  a 
connective  tissue,  and  011  this  account  the  structure  of  the  teeth  is 
considered  here. 


t>on  of  a  human  molar  tooth  ;  c,  cement ;  d,  dentine  ;  e,  enamel 
p,  pulp  cavity.    (Owen.) 
b.  1  lection.    The  letters  indicate  the  i>ame  &>  in  a. 

A  tooth  is  generally  described  as  possessing  a  crown,  neck,  and 
fang  or  fangs. 

F    2 


68 


STRUCTURE    OF    ELEMENTARY    TISSUES.       [chap.  hi. 


The  crown  is  the  portion  which  projects  beyond  the  level  of  the 
givm.  The  neck  is  that  constricted  portion  just  below  the  crown 
which  is  embraced  by  the  free  edges  of  the  gum,  and  the  fang  in- 
cludes all  below  this. 

On  making  a  longitudinal  section  through  the  centre  of  a  tooth 
(figs.  58,  59),  it   is  found  to   be   principally  composed   of  a  hard 

matter,  dentine  or  ivory  ;  while 
in  the  centre  this  dentine  is 
hollowed  out  into  a  cavity  resem- 
bling in  general  shape  the  outline 
of  the  tooth,  and  called  the  pulp 
cavity,  from  its  containing  a  very 
vascular  and  sensitive  little  mass, 
composed  of  connective  -  tissue, 
blood-vessels,  and  nerves,  which 
is  called  the  tooth-pulp. 

The  blood-vessels  and  nerves 
enter  the  pulp  through  a  small 
opening  at  the  extremity  of  the 
fang. 

Capping  that  part  of  the  den- 
tine which  projects  beyond  the 
level  of  the  gum,  is  a  layer  of 
very  hard  calcareous  matter,  the 
enamel  ;  while  sheathing  the  por- 
tion of  dentine  which  is  beneath 
the  level  of  the  gum,  is  a  layer 
of  true  bone,  called  the  cement  or 
crnsta  petrosa. 

At  the  neck  of  the  tooth,  where 
the  enamel  and  cement  come  into 
contact,  each  is  reduced  to  an 
exceedingly  thin  layer.  The 
covering  of  enamel  becomes  thicker  as  we  approach  the  crown,  and 
the  cement  as  we  approach  the  lower  end  or  apex  of  the  fang. 

I. — Dentine. 
Chemical  composition. — Dentine  or  ivory  in  chemical  composition 
closely  resembles  bone.     It  contains,  however,  rather  less  animal 


Fig.  59. — Premolar  tooth  of  cat  in  situ. 
Vertical  section.  1.  Enamel  with 
decussating  and  parallel  stripe.  2. 
Dentine  'with  Sehreger's  lines.  3. 
Cement.  4.  Periosteum  of  the  alve- 
olus. 5.  Inferior  maxillary  hone 
showing  canal  for  the  inferior  dental 
nerve  and  vessels  which  appears 
nearlv  circular  in  transverse  section. 
(Waldeyer.) 


Clf  A  !'.    III.] 


TEETH:     DENTINE. 


69 


matter  ;  the  proportion  in  a  hundred  parts  being  about  twenty- 
eight  animal  to  Beventy-two  of  worthy.  The  former,  like  the 
animal  matter  of  bone,  may  be  resolved  into  gelatin  \>y  boiling. 
The  earthy  matter  is  made  up  chiefly  of  calcium  phosphate,  with  a 

small  portion  of  the  carbonate,  and  traces  of  calcium  fluoride  ami 
gnesium  phosphate. 
Structure. — Under  the  ml  1  denti]  en  to  be  finely 

channelled  by  a  multitude  of  delicate  tubes,  which,  by  their  inner 
ends,  communicate  with  the  pulp-cavity,  and  by  their  outer  ex- 
tremities come  into  contact  with  the  under  part  of  the  enamel  and 


Fig.  €•: .—  -  from  the  m  root  of  an 

a,  den tal  tubuli  ramifying  and  terminating,  some  of  them  in  the  inter- 
globular -  -  nd  <-.  which  somewhat  resemble  bone  laeun*  ;  d.  inner  layer  of  the 
cement  with  numerous  set  canaliculi ;  e,  outer  layer  of  cement ;  /,  lacunie  ; 

•j,  canaliculi. 

cement  and  sometimes  even  penetrate  them  for  a  greater  or  less 
distance  (fig.  60). 

In  their  course  from  the  pulp-cavity  to  the  surface  of  the 
dentine,  the  minute  tubes  form  gentle  and  nearly  parallel  curves 
and    divide    and    subdivide    dichotomously,    but    without    much 

S8ening  of  their  calibre  until  they  are  approaching  their  peri- 
pheral termination. 

From  their  sides  proceed  other  exceedingly  minute  secondary 
canals,  which  extend  into  the  dentine  between  the  tubules,  and 
anastomose  with  each  other.  The  tubules  of  the  dentine,  the 
average  diameter  of  which  at  their  inner  and  larger  extremity  is 
-j-foo  of  an  inch,  contain  fine  prolongations  from  the  tooth-pulp, 
which  Lrive  the  dentine  a  certain  faint  sensitiveness  under  ordi- 
nary circumstances  and,  without  doubt,  have  to  do  also  with  its 
nutrition.  These  prolongations  from  the  tooth-pulp  are  really 
processes  of  the  dentine-cells  or  odontoblasts  which  are  branched 


'0 


8TEUCTUEE    OF    ELEMENTARY    TISSUES.       [chap.  hi. 


cells  lining  the  pulp-cavity  ;  the  relation  of  these  processes  to  the 
tubules  in  which  they  lie  being  precisely  similar  to  that  of  the  pro- 
cesses of  the  hone-corpuscles  to  the  canaliculi  of  bone.  The  outer 
portion  of  the  dentine,  underlying  both  the  cement  and  enamel. 
forms  a  more  or  less  distinct  layer  termed  the  granular  or  inter- 
globular layer.  It  is  characterised  by 
/  the  presence  of  a    number   of  minute 

^rr-^rrn:  ?~~~:r&f  cell-like    cavities,    much    more    closely 

packed  than  the  lacunae  in  the  cement, 
and  coinmunicating  with  one  another 
and  with  the  ends  of  the  dentine-tubes 
(fig.  60),  and  containing  cells  like  bone- 
corpuscles. 


'    - 

- 

-    .-  -  - 

/-■•-.- 


■m 


E'fM 


II. — Enamel. 

Chemical  composition. — The  ena 
which  is  by  far  the  hardest  portion  of 
a  tooth,  is  composed,  chemically,  of  the 
same  elements  that  enter  into  the  com- 
sition  of  dentine  and  bone.  Its  ani- 
mal matter,  however,  amounts  only  to 
about  2  or  3  per  cent.      It  contai: 

_  r  proportion  of  inorganic  matter 
and  is  harder  than  any  other  tissue  in 
the  body. 

Structure.  —  Examined  under  the 
microscope,  enamel  is  found  com] 
of  fine  hexagonal  fibres  _  61.  62) 
50x00  of  an  inch  in  diameter,  which  are 
set  on  end  on  the  surface  of  the  dentine, 
and  fit  into  corresponding  de] 
in  the  same. 

They  radiate  in  such  a  manner  fin  >m 
the  dentine  that  at  the  top  of  the  tooth  they  are  more  or 
vertical,  while  towards  the  sides  they  tend  to  the  horizontal  direc- 
tion. Like  the  dentine  tubules,  they  are  not  Btraight,  but  dis] 
in  wavy  and  parallel  curves.  The  fibres  are  marked  by  transverse 
lines,  and  are  mostly  solid,  but  some  of  them  contain  a  very  minute 
canal. 


Fig.   ci.  —  of    the 

enanf-l  and  a  part 
tine,      a,  cuticular  pellicle    of 
the  enamel :   h.  enamel  fibres, 
or   columns  with  fissures 
tween  them  and  cross  striae  : 
c,  larger  cavities  in  the  enamel, 
communicating  with  the 
mities  of  some  of  the  tufoi  i 
X  350.     (Koll: 


OHAP.  in.] 


DEVELOPMENT  OF  TEETH. 


n 


The  enamel-prisms  are  connected  together  by  a  very 
quantity  of  hyaline  cement-substance.  In  the  deeper  par 
enamel,  between  the  prisms, 
are  small  lacunas,  which  com- 
municate with  the  "  interglo- 
bular spaces"  on  the  surface 
of  the  dentine. 

The  enamel  itself  is  coated 
on  the  outside  by  a  very  thin 
calcified  membrane,  sometimes 
termed  the  cuticle  of  the 
enamel. 

III. — Orusta  Petrosa. 

The  crusta  petrosa,  or  cement 
(fig.  60,  c,  d),  is  composed  of 
true  hone,  and  in  it  are  la- 
cunse  (/)  and  canaliculi  (</) 
which  sometimes  communicate 
with  the  outer  finely  branched 
ends  of  the  dentine  tubules. 
Its  laminae  are  as  it  were 
bolted  together  by  perforating 
fibres  like  those  of  ordinary 
bone,  but  it  differs  in  possess- 
ing Haversian  canals  only  in 
the  thickest  part. 


liiinuto 
t  of  the 


Fig.  62. — Enamel  fibres.  A,  fragments  and 
single  fibres  of  the  enamel,  isolated  by 
the  action  of  hydrochloric  acid.  B,  sur- 
face of  a  small  fragment  of  enamel, 
showing  the  hexagonal  ends  of  the  fibres, 
x  350.     (Kolliker.) 


Development  of  Teeth. 

Development  of  the  Teeth. — The  first  step  in  the  development  of 
the  teeth  consists  in  a  downward  growth  (fig.  63,  a,  i)  from  the 
stratified  epithelium  of  the  mucous  membrane  of  the  mouth,  now 
thickened  in  the  neighbourhood  of  the  maxillae  which  are  in  the 
course  of  formation.  This  process  passes  downward  into  a  recess 
(enamel  groove)  of  the  imperfectly  developed  tissue  of  which  the 
chief  part  of  the  jaw  consists.  The  downward  epithelial  growth 
forms  the  primary  enamel  organ  or  enamel  germ,  and  its  position  is 
indicated  by  a  slight  groove  in  the  mucous  membrane  of  the  jaw. 


72 


STRUCTURE    OF    ELEMENTARY  TISSUES.       [chap.  hi. 


The  next  step  in  the  process  consists  in  the  elongation  downward 
of  the  enamel  groove  and  of  the  enamel  germ  and  the  inclination 
outward  of  the  deeper  part  (fig.  63,  b,  /'),  which  is  now  inclined 
at  an  angle  with  the  upper  portion  or  neck  (/),  and  has  become 


Pig.  63.— Section  of  the  upper  jaw  of  a  fatal  sheep.  A. — I,  common  enamel-germ  dipping- 
down  into  the  mucous  membrane  ;  2,  palatine  process  of  jaw.  B. — Section  similar  to 
A,  but  passing  through  one  of  the  special  enamel-germs  here  becoming  flask-shaped  ; 
c,  c',  epithelium  of  mouth  ;  /,  neck  ;  /',  body  of  special  enamel-germ.  C— A  later 
stage;  c,  outline  of  epithelium  of  gum;  /,  neck  of  enamel-germ;  t ',  enamel  organ - 
P,  papilla;  s,  dental  sac  forming  ;  fp,  the  enamel-germ  of  permanent  tooth.  (Wal- 
deyer  and  Kolliker.)    Copied  from  Quain's  Anatomy. 


bulbous.  After  this,  there  is  an  increased  development  at  certain 
points  corresponding  to  the  situations  of  the  future  milk  teeth, 
and  the  enamel  germ,  or  common  enamel  germ,  as  it  may  be 
called,   becomes  divided   at   its  deeper   portion,  or  extended  by 


CHAP.  III. J 


DEVELOPMENT    OF    TEETH. 


73 


further  growth,  into  a  number  of  specia]   enamel    gem 
sponding  to  each  of  the  above-mentioned  milk  teeth,  and  conni    I 
to  the  common  germ  by  a  narrow  neck,  each  tooth  being  pi 
in  its  own  special  recess  in  the  embryonic  jaw  (fig.  G3,  b,//'). 

Ajg  these  changes  proceed,  there  -rows  up  from  the  underlying 
tissue  into  each  enamel  germ  (fig.  63,  c,  p),  a  distinct  vascular 
papilla  (dental  papilla),  and  upon  it   the  enamel   germ  bea 
moulded  and  presents  the  appearance  of  a  cap  of  two  lay* 
epithelium  separated  by  an  interval  (fig.  63,  c,/  ).     Whilst  part 
of  the  sub-epithelial  tisfi  levated  to  form  the  dental  papillae, 

the  part  which  hounds  the  embryonic  teeth  forms  the  dental  -  - 
(fig.  63,  0,  *)  ;  and  the  rudiment  of  the  jaw,  at  first  a  bony 
gutter  in  which  the  teeth  germs  lie.  sends  up  processes  fonning 
partitions   between  the  teeth.     In  this  way  small  chambers  are 


Pig.  64. — Fart  of  section  of  developing  tooth  of  a  young  rot,  showing  the  mode  of  dei  ri- 
tion  of  the"  dentine.  "  Highly  masnined.  a,  outer  layer  of  fully  formed  dentine ; 
l,  uncalcified  matrix  with  one  or  two  nodules  of  calcareous  matter  near  the  ca". 
parts ;  r,  odontoblasts  sending  processes  into  the  dentine ;  d.  pulp.  The  section  i~ 
stained  in  carmine,  which  colours  the  nncalcified  matrix  but  not  the  calcined  part. 
(E.  A.  Bchafer.] 

produced  in  which  the  dental  sacs  are  contained,  and  thus  the 
sockets  of  the  teeth  are  formed.  The  papilla,  which  is  really 
part  of  the  dental  sac,  if  one  thinks  of  this  as  the  whole  <>f 
the  sub-epithelial  tissue  surrounding  the  enamel  organ  and 
interposed  between  the  enamel  .u-erm  and  the  developing  bony 
jaw,  is  composed  of  nucleated  cells  arranged  in  a  meshwork,  the 
outer  or  peripheral  part  being  covered  with  a  layer  of  columnar 
nucleated  cells  called  odontoblasts.  The  odontoblasts  form  the 
dentine,  while  the  remainder  of  the  papilla  forms  the  tooth-pulp. 
The  method  of  the  formation  of  the  dentine  from  the  odontoblae 
is  as  follows: — The  cells  elongate  at  their  outer  part,  and  th<  - 
processes  are  directly  converted  into  the  tubules  of  dentine  (fig.  64). 


74 


STRUCTURE    OF    ELEMENTARY    TISSUES.      [chap.  hi. 


The  continued  formation  of  dentine  proceeds  by  the  elongation  of 
the  odontoblasts,  and  Their  subsequent  conversion  by  a  process  of 
calcification  into  dentine  tubules.  The  most  recently  formed 
tubules  are  not  immediately  calcified.  The  dentine  fibres  con- 
tained in  the  tubules  are  said  to  be  formed  from  processes  of  the 

deeper  layer  of  odonto- 
blasts, which  are  wedged 
in  between  the  cells  of  the 
superficial  layer  (fig.  64) 
which  form  the  tubules 
only. 

Since  the  papillae  are  to 
form  the  main  portion  of 
each  tooth,  i.e.,  the  dentine, 
each  of  them  early  takes 
the  shape  of  the  crown  of 
the  tooth  it  is  to  form.  As 
the  dentine  increases  in 
thickness,  the  papillae  dimi- 
nish, and  at  last  when  the 
tooth  is  cut,  only  a  small 
amount  of  the  papilla  re- 
mains as  the  dental  pulp, 
and  is  supplied  by  vessels 
and  nerves  which  enter  at 
the  end  of  the  fang.  The 
shape  of  the  crown  of  the 
tooth  is  taken  by  the 
corresponding  papilla,  and 
that  of  the  single  or  double 
fang  by  the  subsequent 
constriction  below  the  crown,  or  by  division  of  the  lower  part  of 
the  papilla. 

The  enamel  cap  is  found  later  on  to  consist  (fig.  65)  of  three  parts  : 
(a)  an  inner  membrane,  composed  of  a  layer  of  columnar  epithe- 
lium m  contact  with  the  dentine,  called  enamel  cell*,  and  outside 
of  these  one  or  more  layers  of  small  polyhedral  nucleated  cells 
{stratum  intermedium  of  Hannover) ;  (I)  an  outer  membrane  of 
several  layers  of  epithelium  ;  (c)  a  middle  membrane  formed  of  a 


Fig  !   trans 


f  tfu   dental 


sac,  pulp,  fee,  of  a  kitten,  n.  dental  papilla 
or  pulp  ;  b.  the  cap  of  dentine  formed  upon 
the  summit ;  c,  its  covering  of  enamel ; 
d,  inner  layer  of  epithelium  of  the  enamel 
organ;  e,  gelatinous  tissue ; /,  outer  epithe- 
lial layer  of  the  enamel  organ  :  g,  inner  layer, 
and  h.  outer  layer  of  dental  sac.  X  14. 
(Thiersch. 


chap.  in. J       DEVELOPMENT  OF  TEETH.  75 

matrix  of  non  vascular,  gelatinous  tissue,  containing  a  hyaline 
interstitial  substance.  The  enamel  is  formed  by  the  enamel 
cells  of  the  inner  membrane,  by  the  elongation  of  their  distal 
extremities,  and  the  direct  conversion  of  these  processes  into 
enamel.  The  calcification  of  the  enamel  processes  or  prisms  takes 
place  first  at  the  periphery,  the  centre  remaining  for  a  time 
transparent.  The  cells  of  the  stratum  intermedium  arc  used  for 
the  regeneration  of  the  enamel  cells,  hut  these  and  the  middle 
membrane  after  a  time  disappear.  The  cells  of  the  outer  mem- 
brane give  origin  to  the  cuticle  of  the  enamel. 

The  cement  or  crusta  petrosa  is  formed  from  the  tissue  of  tie- 
tooth  sac,  the  structure  and  function  of  which  are  identical  with 
those  of  the  osteogenetic  layer  of  the  periosteum. 

In  this  manner  the  first  set  of  teeth,  or  the  milk-teeth,  arc 
formed  ;  and  each  tooth,  by  degrees  developing,  presses  at  length 
on  the  wall  of  the  sac  enclosing  it  and,  causing  its  absorption,  is 
cut,  to  use  a  familiar  phrase. 

The  temporary  or  milk-teeth  have  only  a  very  limited  term  of 
existence.  This  is  due  to  the  growth  of  the  permanent  teeth, 
which  push  their  way  up  from  beneath,  absorbing  in  their  progress 
the  whole  of  the  fang  of  each  milk-tooth  and  leaving  at  length 
only  the  crown  as  a  mere  shell,  which  is  shed  to  make  way  for 
the  eruption  of  the  permanent  teeth  (tig.  66). 

The  temporary  teeth  are  ten  in  each  jaw,  namely,  four  incisors, 
two  canines,  and  four  molars,  and  are  replaced  by  ten  permanent 
teeth,  each  of  which  is  developed  in  a  way  almost  exactly  similar 
to  the  manner  of  development  already  described,  from  a  small 
process  or  sac  set  by,  so  to  speak,  from  the  enamel  germ  of  the 
temporary  tooth  which  precedes  it,  and  called  the  cavity  of  reserve. 

The  number  of  permanent  teeth  in  each  jaw  is,  however,  in- 
creased to  sixteen,  by  the  development  of  three  others  on  each  side 
of  the  jaw  after  much-  the  same  fashion  as  that  by  which  the  milk- 
teeth  were  themselves  formed. 

The  beginning  of  the  development  of  the  permanent  teeth  of 
course  takes  place  long  before  the  cutting  of  those  which  they  are 
to  succeed.  One  of  the  first  steps  in  the  development  of  a  milk- 
tooth  is  the  outgrowth  of  a  lateral  process  of  epithelial  cells  from 
its  primitive  enamel  organ  (fig.  63,  c,  f  p).  This  epithelial  out- 
growth ultimately  becomes  the  enamel  organ  of  the  permanent 


76 


STRUCTURE    OF    ELEMENTARY    TISSUES.      [chap.  tit. 


tooth,  and  is  indented  from  below  by  a  primitive  dental  papilla, 
precisely  as  described  above. 


Fig.  66. — Part  of  the  lower  jaw  of  a  child  of  three  or  four  years  old,  showing  the  relations 
of  the  temporary  and  permanent  teeth.  The  specimen  contains  all  the  milk-teeth  of 
the  right-side,  together  with  the  incisors  of  the  left ;  the  inner  plate  of  the  jaw  has 
been  removed,  so  as  to  expose  the  sacs  of  till  the  permanent  teeth  of  the  right  side, 
except  the  eighth  or  wisdom  tooth,  which  is  not  yet  formed.  The  large  sac  near  the 
ascending  ramus  of  the  jaw  is  that  of  the  first  permanent  molar,  and  above  and  behind 
it  is  the  commencing  rudiment  of  the  second  molar.     (Quain.) 


The  following  formula  shows,  at  a  glance,  the   comparative  ar- 
rangement and  number  of  the  temporary  and  permanent  teeth  : — 


Temporary  Teeth 


MO.    CA.    IX.    (A.    MO. 

Upper  2     i     4     i     2       =  io 


Lower 


20 


2       I       4       I       2 


IO 


Permanent  teeth 


MO.    BI.    CA.    IN.    CA.    BI.    MO. 

Upper       3     2     i     4     i     2     3=  16 


Lower 


=  32 


2       I 


16 


From  this  formula  it  will  be  seen  that  the  two  bicuspid  teeth  in 
the  adult  are  the  successors  of  the  two  molars  in  the  child.  They 
differ  from  them,  however,  in  some  respects,  the  temporary  molar* 
having  a  stronger  likeness  to  the  permanent  than  to  their  imme- 
diate descendants,  the  so-called  bicuspids. 

The  temporary  incisors  and  canines  differ  from  their  successors 
but  little  except  in  their  smaller  size. 

The  following  tables  show  the  average  times  of  eruption  of  the 
Temporary  and  Permanent  teeth.     In  both  cases,  the  eruption  of 


,  n\r.  in.]  ERUPTION    OP   THE   TEETH.  yy 

any  given  tooth  of  the  lower  jaw  precedes,  as  a  rule,  that  of  the 
corresponding  tooth  of  the  upper. 

/  mporary  or  Milk  Teeth. 
The  figures  indicate  in  month*  the  age  at  which  ca<-h  tooth  appears. 

CANINES.  rCISOBS.        CANINES. 


24    12  iS         9  7  7  9 


12    24 


Per  mi, 1  hi  nt  Teeth. 
The  age  at  which  each  tooth  is  cut  is  indicated  in  this  table  in  years. 

■OLABS.        BICUSPID.        CANINE8.       INi     -       -       l    LXINE8.        BICUSPID.  M< 


17 

12 

12 

17 

to 

to  6 

10 

9 

11  to  12 

8778 

n  to  12 

9 

10 

6  to 

to 

-5 

13 

13 

25 

The  times  of  eruption  put  down  in  the  above  tables  are  only 
approximate  :  the  limits  of  variation  being  tolerably  wide.  Some 
children  may  cut  their  first  teeth  before  the  age  of  six  months  and 
others  not  till  nearly  the  twelfth  month.  In  nearly  all  eases  the 
two  central  incisors  of  the  lower  jaw  are  cut  first  ;  these  being  suc- 
ceeded after  a  short  interval  by  the  four  incisors  of  the  upper  jaw, 
next  follow  the  lateral  incisors  of  the  lower  jaw,  and  so  on  as  indi- 
cated in  the  table  till  the  completion  of  the  milk  dentition  at 
about  the  age  of  two  years. 

The  milk-teeth  usually  come  through  in  batches,  each  period  of 
eruption  being  succeeded  by  one  of  quiescence  lasting  sometimes 
several  months.  The  milk-teeth  are  in  use  from  the  age  of  two 
up  to  five  and  a  half  years  :  at  about  this  age  the  first  permanent 
molars  (four  in  number)  make  their  appearance  behind  the  milk- 
molars,  and  for  a  short  time  the  child  has  four  permanent  and 
twenty  temporary  teeth  in  position  at  once. 

It  is  worthy  of  note  that  from  the  age  of  five  years  to  the 
shedding  of  the  first  milk-tooth  the  child  has  no  fewer  than  forty- 
eight  teeth,  twenty  milk-teeth  and  twenty-eight  calcified  germ-,  of 
permanent  teeth  (all  in  fact  except  the  four  wisdom  teeth). 


jS  THE    BLOOD.  [chap.  iv. 


CHAPTER    IV. 

THE    BLOOD. 

The  blood  of  man,  us  indeed  of  the  great  majority  of  verte- 
brate animals,  is  a  more  or  less  viscid  fluid,  of  a  red  colour.  The 
exact  shade  of  red  is  variable,  for  whereas  that  taken  from  the 
arteries,  from  the  left  side  of  the  heart  or  from  the  pulmonary 
veins,  is  of  a  bright  scarlet  hue,  that  obtained  from  the  systemic 
veins,  from  the  right  side  of  the  heart,  or  from  the  pulmonary 
artery,  is  of  a  mnch  darker  colour,  and  varies  from  bluish-red  to 
reddish-black.  To  the  naked  eye,  the  red  colour  appears  to  belong- 
to  the  whole  mass  of  blood,  but  on  examination  with  the  micro- 
scope it  is  found  that  this  is  not  the  case.  By  the  aid  of  this 
instrument  the  blood  is  shown  to  consist  in  reality  of  an  almost 
colourless  fluid,  called  Liquor.  Sanguinis  or  Plasma,  in  which  are 
suspended  numerous  minute  rounded  masses  of  protoplasm, 
called  Blood  Corpuscles.  The  corpuscles  are,  for  the  most  part, 
coloured,  and  it  is  to  their  presence  that  the  red  colour  of  the 
blood  is  due. 

Even  when  examined  in  very  thin  layers  blood  is  opaque,  on 
account  of  the  different  refractive  powers  possessed  by  its  two 
constituents,  viz.,  the  plasma  and  the  corpuscles.  On  treatment 
with  chloroform  and  other  reagents,  however,  it  becomes  trans- 
parent, and  assumes  a  lake  colour,  in  consequence  of  the  colouring 
matter  of  the  corpuscles  having  been,  by  these  means,  dis- 
charged into  the  plasma.  The  average  specific  gravity  of  blood 
at  6o°F.  (150  C.)  is  1055,  tne  extremes  consistent  with  health 
being  1045- 106 2.  The  reaction  of  blood  is  faintly  alkaline.  Its. 
temperature  varies  within  narrow  limits,  the  average  being 
ioo°  F.  (37 '8°  C).  The  blood  stream  is  slightly  warmed  by  | 
ing  through  the  muscles,  nerve  centres,  and  glands,  but  is  some- 
what cooled  on  traversing  the  capillaries  of  the  skin.  Eecently 
drawn  blood  has  a  distinct  odour,  which  in  many  cases  is  charac- 
teristic of  the  animal  from  which  it  has  been  taken;  the  odour 
mav  be  further  developed  by  adding  to  blood  a  mixture  of  equal 
I  arts  of  sulphuric  acid  and  water. 


.  ii.vi-.  iv.]  ANTITY   OF    BLOOD. 

Quantity   of    the    Blood. — The    quantity    «»f  blood    in 
animal  under  normal  conditi  it  relati 

.it.      The  methods  employed  it 

not  so  simple   as    migl  I      t    I    it    sight    be    thought.      For 

mple,  it  would  to  get  an  .mtc  informa- 

;  <>n  the  point  from  the  amount  obtained  by  rapidly  bl< 
an   animal   I  th,   for    then    an    indefinite    quanta!  ild 

remain  in  the   vess  la,      l  well      s  in  tJ  Q    ' 

other   han«.l,  would   it   be   possible  *        I  in  a  eon 
by  less   rapid    bleeding     a,  am      lii  more  prolonged, 

time  would  be  all  r  the  j    -     _      into  the  blood  of  lymph 

from  the  lymphatic  toss  m  the  tisa  tea.     In  the  form 

ae,  therefore,  we  should  nnder-eatimate,  and  in  the  latter  over- 
>tal  amount  of  the  blood. 
-  era!  methods  which  have  been  employed,  the  u 
accurate  appears  to  be  the  following.  A  small  quantity  of  blood 
is  taken  from  an  animal  by  venesection  :  it  is  defibrinated  an  I 
measured,  and  used  t<j  make  standard  solutions  of  blood.  The 
animal  is  then  rapidly  bled  to  death,  and  the  blood  which  esca:  a 
is  collected.     The  blood  vessels  are  next  washed  out  with  wat 

ne  solution   until    the   washings  are  no  longer  coloured,  and 
these  are  added  to  the  previously   withdrawn  blood  :  lastly  the 
whole  animal  is  finely  minced  with  water  or  saline  solution.      The 
fluid  obtained  fr<:>ni  the  minci:._-  is  sarefully  filtered,  and  added  * 
the  diluted  blood  previou-  f   ined.  and  the  whole  is  measured. 

The  ik   t   st    i  in  the  process   is  the       m]  iris  n  of  the  colour  of 
the  diluted  blood  with  that  of  standard  solut:  blood  and 

wat  known  strength,  imtil  it  is  red  to  what  stan- 

dard  solution  the   diluted   bloo:  the  amount 

of  blood  in  the  nding    standard   solution    is    known. 

.1   as  tl.     total   quantity  of  diluted  blood  obtained  from  * 
animal,   it  Iculate   the    al  amount    of  blood 

which    the    latl  ntained,    and    to    this    is    added    the   small 

amount   which  was   withdrawn  to  make   the   standard  soluti< 
This  irives  the  total  amount  of  blood  which  the  animal  contained. 
It   is    cent  with    the    weight    of    the    anim 

known.     T  rait  of  many  experime:.*     -        3  that  the  quan- 

tity of  blood  in  various  animal<         ■    _   -    _'_    to  ^  of  the  total 
body  weight. 


SO  THE    BLOOD.  [OHAP.  iv. 

An  estimate  of  the  quantity  in  man  which  corresponded  nearly 
-with  the  above,  was  made  some  years  ago  from  the  following  data. 
A  criminal  was  weighed  before  and  after  decapitation  \  the  differ- 
ence in  the  weight  representing,  of  course,  the  quantity  of  blood 
which  escaped.  The  blood-vessels  of  the  head  and  trunk  were 
then  washed  out  by  the  injection  of  water,  until  the  fluid  which 
escaped  had  only  a  pale  red  or  straw  colour.  This  fluid  was  then 
also  weighed  ;  and  the  amount  of  blood  which  it  represented  was 
calculated  by  com] taring  the  proportion  of  solid  matter  contained 
in  it  with  that  of  the  first  blood  which  escaped  on  decapitation. 
Two  experiments  of  this  kind  gave  precisely  similar  results. 
(Weber  and  Lehmann.) 

It  should  be  remembered,  however,  in  connection  with  these 
estimations,  that  the  quantity  of  the  blood  must  vary,  even  in  the 
same  animal,  very  considerably  with  the  amount  of  both  the  in 
gesta  and  egesta  of  the  period  immediately  preceding  the  experi- 
ment ;  and  it  has  been  found,  indeed,  that  the  quantity  of  blood 
obtainable  from  a  fasting  animal  barely  exceeds  a  half  of  that 
which  is  present  soon  after  a  full  meal. 

Coagulation  of  trie  Blood. — One  of  the  most  characteristic 
properties  which  the  blood  possesses  is  that  of  clotting  or  coagulating, 
when  removed  from  the  body.  This  phenomenon  may  be  observed 
under  the  most  favourable  conditions  in  blood  which  has  been 
drawn  into  an  open  vessel.  In  about  two  or  three  minutes,  at  the 
ordinary  temperature  of  the  air,  the  surface  of  the  fluid  is  seen  to 
become  semi-solid  or  jelly-like  ;  this  change  next  taking  place,  in 
a  minute  or  two,  at  the  sides  of  the  vessel  in  which  it  is  contained, 
and  then  extending  throughout  the  entire  mass. 

The  time  which  is  required  for  the  blood  to  become  solid 
is  about  eight  or  nine  minutes.  The  solid  mass  occupies  exactly 
the  same  volume  as  the  previously  liquid  blood,  and  adheres  so 
closely  to  the  sides  of  the  containing  vessel  that  if  it  be  inverted 
none  of  its  contents  escape.  The  solid  mass  is  the  crassamentum 
or  clot.  If  the  clot  be  watched  for  a  few  minutes,  drops  of  a 
light,  straw-coloured  fluid,  the  serum,  may  be  seen  to  make 
their  appearance  on  the  surface  and,  as  they  become  more  and 
more  numerous,  run  together,  forming  a  complete  superficial 
stratum  above  the  solid  clot.  At  the  same  time  the  fluid  begins 
to    transude    at   the    sides  and  at  the  under  surface  of  the  clot, 


(  II  \l'.    IV.] 


i  o  v.i  i. \i  \<>s. 


Hi 


which   in  the  course  of  an    hour  or   two    floats    in    the    liquid. 
The  Bret  dr  rum  appear  on  tin-  surface  about   eleven  or 

twelve  minutes  after  the  blood  has  been  drawn  ;  and  the  fluid  con- 
tinues to  transude  for  from  thirty-sis  to  forty-eight  hours. 

The  clotting  of  blood  is  due  to  the  development  in  it  of  a  sub- 
Btance  called  Jibrin,  which  appears  as  a  meshwork  (fig.  67)  of  fine 
fibrils.  Tlii-  m<  sh- 
work  entangles  and 
encloses  within  it  the 
blood  corpuscles, 
clotting  takes  pli 
too  quickly  to  allow 
them  to  >ink  to  the 
bottom  of  the  plasma. 
The  first  clot  formed, 
therefore,  includes  the 
whole  of  the  consti- 
tuents of  the  blood 
in  an  apparently  solid 
mass,  but  soon  the 
fibrinous      mesh  work 

begins  to  contract,  and  the  .serum  which  does  not  belong  to  the  clot 
ueezed  out.  When  the  whole  of  the  serum  has  transuded, 
the  clot  is  found  to  be  smaller,  but  firmer  and  harder,  as  it  is  now 
made  up  of  fibrin  and  blood  corpuscles  only.  It  will  be  noticed 
that  coagulation  rearranges  the  constituents  of  the  blood  according 
to  the  following  scheme,  liquid  blood  being  made  up  of  plasma 
and  blood-corpuscles,  and  clotted  blood  of  serum  and  clot. 

Liquid  Blood. 


Fig.  67.— /'••  '  "'■■    ••  from  a  drop  of  human  blood, 

after  treatment  with  rosanilin.      Ram  i- 


Plasma 


Corp. 


Serum 


Fibrin 


Clot 


Clotted  Blood 

Buflfy  Coat.— 1  fader  ordinary  circumstances  coagulation  occurs, 

as  we  have  mentioned  above,  before   the   red   corpuscles  have    had 

G 


82  THE    BLOOD.  [CHAP.  iv. 

time  to  subside;  and  thus  from  their  being  entangled  in  the 
meshes  of  the  fibrin,  the  clot  is  of  a  deep  red  colour  throughout, 
somewhat  darker,  it  may  be,  at  the  most  dependent  part,  from 
accumulation  of  red  corpuscles,  but  not  to  any  very  marked  degree. 
When,  however,  coagulation  is  delayed  from  any  cause,  as  when 
blood  is  kept  at  a  temperature  of  32"  F.  (o°  C),  or  when  clotting 
is  normally  a  slow  process,  as  in  the  case  of  horse's  blood,  or,  lastly, 
in  certain  diseased  conditions  of  the  blood  in  which  clotting  is 
naturally  delayed,  time  is  allowed  for  the  coloured  corpuscles 
to  sink  to  the  bottom  of  the  fluid.  When  clotting  does  occur,  the 
upper  layers  of  the  blood,  being  free  of  coloured  corpuscles  and 
counting  chiefly  of  fibrin,  form  a  superficial  stratum  differing  in 
appearance  from  the  rest  of  the  clot,  in  that  it  is  of  a  grayish 
yellow  colour.     This  i<  known  as  the  "  huffy  coat.''' 

Cupped  appearance  of  the  Clot. — When  the  bufly  coat  has 
been  produced  in  the  manner  just  described,  it  commonly  contracts 
more  than  the  rest  of  the  clot,  on  account  of  the  absence  of 
coloured  corpuscles  from  its  meshes,  and  because  contraction  is  less 
interfered  with  by  adhesion  to  the  interior  of  the  containing 
vessel  in  the  vertical  than  the  horizontal  direction.  This  pro- 
duces a  cup-like  appearance  of  the  buffy  coat,  and  the  clot  is  not 
only  buffed  but  cupped  on  the  surface.  The  buffed  and  cupped 
appearance  of  the  clot  is  well  marked  in  certain  states  of  the 
astern,  especially  in  inflammation,  where  the  fibrin-forming  con- 
stituents are  in  excess,  and  it  is  also  well  marked  in  chlorosis 
where  the  corpuscles  are  deficient  in  quantity. 

Formation  of  Fibrin. — In  describing  the  coagulation  of  the 
blood  in  the  preceding  paragraphs,  it  was  stated  that  this  phe- 
nomenon was  due  to  the  development  in  the  clotting  blood  of 
a  meshwork  of  fibrin.  This  may  be  demonstrated  by  taking 
recently-drawn  blood,  and  whipping  it  with  a  bundle  of  twigs  ;  the 
fibrin  is  found  to  adhere  to  the  twigs  as  a  reddish-white,  stringy 
mass,  having  been  thus  obtained  from  the  fluid  nearly  free  from 
coloured  corpuscles.  The  defibrinated  blood  no  longer  retains  the 
power  of  spontaneous  coagulability. 

The  fibrin  which  makes  its  appearance  in  the  blood  when  it  is 
undergoing  coagulation  is  derived  chiefly,  if  not  entirely,  from  the 
plasma  or  liquor  sanguinis ;  for  although  the  colourless  corpuscles 
are  intimatelv  connected  with  the  process  in  a  way  which  will  be 


CBAP.  iv.]  PLASMA.  $$ 

presently  explained,  the  coloured  corpuscles  appear  to  take  no 
active  part  in  it  whatever.  This  may  be  shown  by  experimenting 
with  plasma  free  from  coloured  corpuscles.  Such  plasma  may  be 
procured  by  delaying  coagulation  in  blood,  by  keeping  it  at  a  low 
temperature,  320  F,  (o°  (.'.),  until  the  coloured  corpuscles  which 
aiv  of  higher  specific  gravity  than  the  other  constituents  of  blood, 
have  had  time  to  sink  to  the  bottom  of  the  containing  vessel, 
and  to  leave  an  upper  .stratum  of  colourless  plasma,  in  the  lower 
Layers  of  which  are  many  colourless  corpuscles.  The  blood  of  the 
horse  is  specially  suited  for  the  purposes  of  this  experiment ;  and 
the  upper  stratum  of  colourless  plasma  derived  from  it,  if  decanted 
into  another  vessel  and  exposed  to  the  ordinary  temperature  of 
the  air,  will  coagulate  just  as  though  it  were  the  entire  blood, 
producing  a  clot  similar  in  all  respects  to  blood  clot,  except 
that  it  is  almost  colourless  from  the  absence  of  red  corpuscles. 
If  some  of  the  plasma  be  diluted  with  *  neutral  saline  solution, 
coagulation  is  delayed,  and  the  stages  of  the  gradual  formation 
of  fibrin  may  be  more  conveniently  watched.  The  viscidity 
which  precedes  the  complete  coagulation  may  be  seen  to  be 
due  to  fibrin  fibrils  developing  in  the  fluid — first  of  all  at  the 
circumference  of  the  containing  vessel,  and  gradually  extending 
throughout  the  mass.  Again,  if  plasma  be  whipped  with  a 
bundle  of  twigs,  the  fibrin  may  be  obtained  as  a  solid,  stringy 
mass,  just  in  the  same  way  as  from  the  entire  blood,  and 
the  resulting  fluid  no  longer  retains  its  power  of  spontaneous 
coagulability.  Evidently,  therefore,  fibrin  is  derived  from  the 
plasma  and  not  from  the  coloured  corpuscles.  In  these  ex- 
periments, it  is  not  necessary  that  the  plasma  shall  have  been 
obtained  by  the  process  of  cooling  above  described,  as  plasma 
obtained  in  any  other  way,  e.g.,  by  allowing  blood  to  flow  direct 
from  the  vessels  of  an  animal  into  a  vessel  containing  a  third 
or  a  fourth  of  the  bulk  of  the  blood  of  a  saturated  solution  of  a 
neutral  salt  (preferably  of  magnesium  sulphate)  and  mixing  care- 
fully, will  answer  the  purpose  and,  just  as  in  the  other  case  the 
coloured  corpuscles  will  subside  leaving  the  clear  superstratum  of 

*  Neutral  saline  solution  commonly  consists  of  a  75  solution  of  common 
salt  (sodium  chloride)  in  water. 

g  2 


8/|  Till-;    BLOOD.  [chap.  iv. 

(salted)  plasma.  In  order  to  cause  this  plasma  to  coagulate,  it  is 
necessary  to  get  rid  of  the  salts  by  dialysis,  or  to  dilute  it  with 
several  times  its  bulk  of  water. 

The  antecedent  of  Fibrin. — If  plasma  he  saturated  with  solid 
magnesium  sulphate  or  sodium  chloride,  a  white,  sticky,  precipitate 
called  plasmine  is  thrown  down,  after  the  removal  of  which,  by  filtra- 
tion, the  plasma  will  not  spontaneously  coagulate.  This  plasmine 
is  soluble  in  dilute  neutral  saline  solutions,  and  the  solution  of  it 
speedily  coagulates,  producing  a  clot  composed  of  fibrin.  From 
this  we  see  that  blood  plasma  contains  a  substance  without  which 
it  cannot  coagulate,  and  a  solution  of  which  is  spontaneously 
coagulable.  This  substance  is  very  soluble  in  dilute  saline  solutions, 
and  is  not,  therefore,  fibrin,  which  is  insoluble  in  these  fluids. 
We  are.  therefore,  led  to  the  belief  that  plasmine  produces  or  is  con- 
verted into  fibrin,  when  clotting  of  fluids  containing  it  takes  place. 

Nature  of  Plasmine. — There  seems  distinct  evidence  that 
plasmine  is  a  compound  body  made  up  of  two  or  more  substances, 
and  that  it  is  not  mere  soluble  fibrin.  This  view  is  based  upon 
the  following  observations  : — There  exists  in  all  the  serous  cavities 
of  the  body  in  health,  e.g.,  the  pericardium,  the  peritoneum,  and 
the  pleura,  a  certain  small  amount  of  transparent  fluid,  generally 
of  a  pale  straw  col<  air,  which  in  diseased  conditions  may  be  greatly 
increased.  It  somewhat  resembles  serum  in  appearance,  but  in 
reality  differs  from  it,  and  is  probably  identical  with  plasma.  This 
serous  fluid  is  not,  as  a  rule,  spontaneously  coagulable,  but  may  be 
made  to  clot  on  the  addition  of  serum,  which  is  also  a  fluid  which 
has  no  tendency  of  itself  to  coagulate.  The  clot  produced  consists 
of  fibrin,  and  the  clotting  is  identical  with  the  clotting  of  plasma. 
From  the  serous  fluid  (that  from  the  inflamed  tunica  vaginalis  testis 
or  hydrocele  fluid  is  mostly  used)  we  may  obtain,  by  saturating  it 
with  solid  magnesium  sulphate  or  sodium  chloride,  a  white  viscid 
substance  as  a  precipitate  which  is  called  fibrinogen,  which  may 
be  separated  by  filtration,  and  is  then  capable  of  being  dissolved 
in  water,  as  a  certain  amount  of  the  neutral  salt  is  entangled 
with  the  precipitate  sufficient  to  produce  a  dilute  saline  solu- 
tion in  which  it  is  soluble.  This  body  belongs  to  the  globulin 
class  of  proteid  substances.  Its  solution  has  no  tendency  to 
clot  of   itself.      Fibrinogen    may    also    be    obtained    as    a   viscid 


i hap.  iv.]  PARAGLOBULIN :  FIBRIN   FERMENT.  S'- 

precipitate  from  hydrocele  fluid  by  diluting  it  with  water,  and 
passing  a  brisk  stream  of  carbon  dioxide  gas  through  the  solu- 
tion.    Now   if  serum   be  added  t<»  a  solution   of  fibrinogen,  the 

uii\t lire  dots. 

From  serum  may  be  obtained  another  globulin  very  similar  in 
properties  to  fibrinogen,  if  it  be  subjected  to  treatment  similar  to 
either  of  the  two  methods  by  which  fibrinogen  is  obtained  from 
hydrocele  fluid  ;  this  substance  is  called  paraglobulin,  and  it  may 
be  separated  by  filtration  and  dissolved  in  a  dilute  saline  solution 
in  a  manner  similar  to  fibrinogen. 

If  the  solutions  of  fibrinogen  and  paraglobulin  be  mixed,  the 
mixture  cannot  be  distinguished  from  a  solution  of  plasmine,  and 
like  that  solution  (in  a  great  majority  of  eases)  firmly  clots 
whereas  a  mixture  of  the  hydrocele  fluid  and  serum,  from  which 
they  have  been  respectively  taken,  no  longer  does  so.  In  addition 
to  this  evidence  of  the  compound  nature  of  plasmine,  it  may  lie 
further  shown  that,  if  sufficient  care  be  taken,  both  fibrinogen  and 
paraglobulin  may  be  obtained  from  plasma  :  fibrinogen,  as  a  flaky 
precipitate,  by  adding  carefully  13  per  cent,  of  crystalline  sodium, 
chloride  ;  and  after  the  removal  of  fibrinogen  from  the  plasma  by 
filtration,  paraglobulin  may  be  afterwards  precipitated,  on  th 
further  addition  of  the  same  salt  or  of  magnesium  sulphate  to 
the  filtrate.  It  is  evident,  therefore,  that  both  these  substances 
must  be  thrown  down  together  when  plasma  is  saturated  with 
sodium  chloride  or  magnesium  sulphate,  and  that  the  mixture  of 
the  two  corresponds  with  plasmine. 

Presence  of  a  Fibrin  Ferment. — So  far  it  has  been  shown 
that  plasmine,  the  antecedent  of  fibrin  in  blood,  to  the  possession 
of  which  blood  owes  its  power  of  coagulating,  is  not  a  simple  body, 
but  is  composed  of  at  least  two  factors — viz.,  fibrinogen  and  para- 
globulin ;  there  is  reason  for  believing  that  yet  another  body  is 
associated  with  them  in  plasmine  to  produce  coagulation  :  this 
is  what  is  known  under  the  name  of •  fibrin  ferment  (Schmidt).  It 
was  at  one  time  thought  that  the  reason  why  hydrocele  fluid 
coagulated  when  serum  was  added  to  it  was  that  the  latter  fluid 
supplied  the  paraglobulin  which  the  former  lacked  ;  this,  however, 
is  not  the  case,  as  hydrocele  does  not  lack  this  body,  and  if 
paraglobulin,  obtained  from  serum  by  the  carbonic  acid  method, 
be   added    to    it,    it    will    not   coagulate,    neither   will   a    mixture 


86  THE    BLOOD.  [chap.  iv. 

of  solutions  of  fibrinogen  and  paraglobulin  obtained  in  the 
same  way.  But  if  paraglobulin,  obtained  by  the  saturation 
method,  be  added  to  hydrocele  fluid,  it  will  clot,  as  will  also,  as 
we  have  seen  above,  a  mixed  solution  of  fibrinogen  and  paraglo- 
bulin, when  obtained  by  the  saturation  method.  From  this  it  is 
evident  that  in  plasmine  there  is  something  more  than  the  two 
bodies  above  mentioned,  and  that  this  something  is  precipitated 
with  the  paraglobulin  by  the  saturation  method,  and  is  not  pre- 
cipitated by  the  carbonic  acid  method.  The  following  experiments 
show  that  it  is  of  the  nature  of  a  ferment.  If  defibrinated  blood  or 
serum  be  kept  in  a  stoppered  bottle  with  its  own  bulk  of  alcohol 
for  some  weeks,  all  the  proteid  matter  is  precipitated  in  a  coagu- 
lated form;  if  the  precipitate  be  then  removed  by  filtration,  dried 
over  sulphuric  acid,  finely  powdered,  and  then  suspended  in  water, 
a  watery  extract  may  be  obtained  by  further  filtration,  containing 
extremely  little,  if  any,  proteid  matter.  Yet  a  little  of  this  watery 
extract  will  determine  coagulation  in  fluids,  e.g.,  hydrocele  fluid 
or  diluted  plasma,  which  are  not  spontaneously  coagulable,  or 
which  coagulate  slowly  and  with  difficulty.  It  will  also  cause  a 
mixture  of  fibrinogen  and  paraglobulin,  obtained  by  the  carbonic 
acid  method,  to  clot.  This  watery  extract  appears  to  contain  the 
body  which  is  precipitated  with  the  paraglobulin  by  the  saturation 
method.  Its  active  properties  are  entirely  destroyed  by  boiling. 
The  amount  of  the  extract  added  does  not  influence  the  amount  of 
the  clot  formed,  but  only  the  rapidity  of  clotting,  and  moreover 
the  active  substance  contained  in  the  extract  evidently  does  not 
form  part  of  the  clot,  as  it  may  be  obtained  from  the  serum  after 
blood  has  clotted.  So  that  the  third  factor,  which  is  contained 
in  the  aqueous  extract  of  blood,  belongs  to  that  class  of  bodies 
which  promote  the  union  of  other  bodies,  or  cause  changes  in  other 
bodies,  without  themselves  entering  into  union  or  undergoing 
change,  i.e.  ferments.  The  third  substance  has,  therefore,  received 
the  name  Jibrin  ferment.  This  ferment  is  developed  in  blood  soon 
after  it  has  been  shed,  and  its  amount  appears  to  increase  for  a 
certain  time  afterwards  (p.  92). 

The  part  played  by  Paraglobulin. — So  far  we  have  seen  that 
plasmine  is   a  body  composed  of  three  substances,  viz.,  fibrinogen 
paraglobulin,  and  fibrin  ferment.     The  question  presents  itself,  are 
these  three  bodies  actively  concerned  in  the  formation  of  fibrin  ? 


OHAP.  iv.]  COAGULATION.  87 

Bere  we  come  to  a  point  about  which  two  distinct  opinions  pre- 
vail, and  which  it  will   be  necessary  to  mention     Schmidt  holds 

that   fibrin  is  produced   by  the  interaction   of  the   two   proteid 
bodies,  viz.,  fibrinogen   and  paraglobulin,  brought  about  by  the 

presence  of  a  special  fibrin  ferment.  Also,  that  when  coagulation 
does  not  occur  in  serum,  which  contains  paraglobulin  and  the 
fibrin  ferment,  the  non-coagulation  is  accounted  for  by  luck  of 
fibrinogen,  and  when  it  does  not  occur  in  fluids  which  contain 
fibrinogen,  it  is  due  to  the  absence  of  paraglobulin,  or  of  the 
ferment,  or  of  both.  It  will  be  seen  that,  according  to  this  view, 
paraglobulin  has  a  very  important  hbrino-plastic  property.  The 
other  opinion,  held  by  Hammersten,  is  that  paraglobulin  is  not 
an  essential  in  coagulation,  or  at  any  rate  does  not  take  an  active 
part  in  the  process.  He  believes  that  paraglobulin  possesses  the 
property  in  common  with  many  other  bodies  of  combining  with — 
or  decomposing,  and  so  rendering  inert — certain  substances  which 
have  the  power  of  preventing  the  formation  or  precipitation  of 
fibrin,  this  power  of  preventing  coagulation  being  well  known  to 
belong  to  the  free  alkalies,  to  the  alkaline  carbonates,  and  to 
certain  salts ;  and  he  looks  upon  fibrin  as  formed  from  fibrinogen, 
which  is  either  (1)  decomposed  into  that  substance  with  the  pro- 
duction of  some  other  substances  ;  or  (2)  bodily  converted  into 
it  under  the  action  of  a  ferment,  which  is  frequently  precipitated 
with  paraglobulin. 

Influence  of  Salts  on  Coagulation. — It  is  believed  that  the 
presence  of  a  certain  but  small  amount  of  salts,  especially  of 
sodium  chloride,  is  necessary  for  coagulation,  and  that  without  it, 
clotting  cannot  take  place. 

Sources  of  the  Fibrin  Generators. — It  has  been  previously 
remarked  that  the  colourless  corpuscles  which  are  always  present 
in  smaller  or  greater  numbers  in  the  plasma,  even  when  this 
has  been  freed  from  coloured  corpuscles,  have  an  important 
share  in  the  production  of  the  clot.  The  proofs  of  this  may  be 
briefly  summarised  as  follows  : — (1)  That  all  strongly  coagulable 
fluids  contain  colourless  corpuscles  almost  in  direct  proportion  to 
their  coagulability;  (2)  That  clots  formed  on  foreign  bodies,  such 
as  needles  inserted  into  the  interior  of  living  blood-vessels,  are 
preceded  by  an  aggregation  of  colourless  corpuscles  ;  (3)  That 
plasma  in  which  the  colourless  corpuscles  happen  to  be  scanty, 


$8  J  in:  blood.  [.hap.  iv. 

clots  feebly  ;  (4)  That  if  horse's  blood  be  kept  in  the  cold,  so  that 
the  corpuscles  subside,  it  will  be  found  that  the  lowest  stratum, 
containing  chiefly  coloured  corpuscles,  will,  if  removed,  clot  feebly, 
as  it  contains  little  of  the  fibrin  factors;  whereas  the  colourless 
plasma,  especially  the  lower  layers  of  it  in  which  the  colourless 
corpuscles  are  most  numerous,  will  clot  well,  but  if  filtered  in 
the  cold  will  not  clot  so  well,  indicating  that  when  filtered  nearly 
free  from  colourless  corpuscles  even  the  plasma  does  not  contain 
sufficient  of  all  the  fibrin  factors  to  produce  thorough  coagulation  ; 
(5)  In  a  drop  of  coagulating  blood,  observed  under  the  microscope, 
the  fibrin  fibrils  are  seen  to  start  from  the  colourless  corpuscles. 

Although  the  intimate  connection  of  the  colourless  corpuscles 
with  the  process  of  coagulation  seems  indubitable,  for  the  reasons 
just  given,  the  exact  share  which  they  have  in  contributing  the 
various  fibrin  factors  remains  still  uncertain.  It  is  generally 
believed  that  the  fibrin-ferment  at  any  rate  is  contributed  by 
them,  inasmuch  as  the  quantity  of  this  substance  obtainable  from 
plasma  bears  a  direct  relation  to  the  numbers  of  colourless 
corpuscles  which  the  plasma  contains.  Many  believe  that  the 
fibrinogen  also  is  wholly  or  in  part  derived  from  them. 

Conditions  affecting  Coagulation. — The  coagulation  of  the 
blood  is  hastened  by  the  following  means  : — 

1.  Moderate  warmth, — from  about  ioo°  to  120°  F.  (37*8 — 

49°  C). 

2.  Rest  is  favourable  to  the  coagulation  of  blood.  Blood,  of 
which  the  whole  mass  is  kept  in  uniform  motion,  as  when  a  closed 
vessel  completely  filled  with  it  is  constantly  moved,  coagulates 
very  slowly  and  imperfectly. 

3.  Contact  with  foreign  matter,  and  especially  multipli- 
cation of  the  points  of  contact.  Thus,  coagulated  fibrin  may 
be  quickly  obtained  from  liquid  blood  by  stirring  it  with  a  bundle 
of  small  twigs  ;  and  even  in  the  living  body  the  blood  will  coagu- 
late upon  rough  bodies  projecting  into  the  vessels;  as,  for  ex- 
ample, upon  threads  passed  through  them,  or  upon  the  heart's 
valves  roughened  by  inflammatory  deposits  or  calcareous  accumu- 
lations. 

4.  The  free  access  of  air. — Coagulation  is  quicker  in  shallow 
than  in  tall  and  narrow  vessels. 


chap,  iv.]       CONDITIONS    AFFECTING    COAGULATION.  89 

5.   The  addition  of  loss  than  twice  the  bulk  of  water. 

The  blood  last  drawn  is  said  to  coagulate  more  quickly  than  the 
•  ret 

The  coagulation  of  the  blood  is  retarded,  suspended,  or 
prevented  by  the  following  means  : — 

1.  Cold  retards  coagulation  ;  and  s<»  long  as  Mood  is  kept  at  a 
temperature,  320  l\  (o°(\),  it  will  not  coagulate  at  all.  Freezing 
the  blood,  of  course,  prevents  its  coagulation  ;  vet  it  will  coagu- 
late, though  not  firmly,  if  thawed  after  being  frozen;  and  it  will 
do  so,  even  after  it  has  been  frozen  for  several  months.  A 
higher  temperature  than  1200  F.  (490  C.)  retards  coagulation 
or,  by  coagulating  the  albumen  of  the  serum,  prevents  it 
altogether. 

2.  The  addition  of  water  in  greater  proportion  than  twice 
the  bulk  of  the  blood. 

3.  Contact  with  living  tissues,  and  especially  with  the 
interior  of  a  living  blood-vessel. 

4.  The  addition  of  neutral  salts  in  the  proportion  of  2  or  3 
per  cent,  and  upwards.  When  added  in  large  proportion  most  of 
these  saline  substances  prevent  coagulation  altogether.  Coagula- 
tion, however,  ensues  on  dilution  with  water.  The  time  during 
which  blood  can  be  thus  preserved  in  a  liquid  state  and  coagulated 
by  the  addition  of  water,  is  quite  indefinite. 

5.  Imperfect  aeration, — as  in  the  blood  of  those  who  die 
by  asphyxia. 

G.  In  inflammatory  states  of  the  system  the  blood  coagu- 
lates more  slowly  although  more  firmly. 

7.  Coagulation  is  retarded  by  exclusion  of  the  blood  from 
the  air,  as  by  pouring  oil  on  the  surface,  etc.  In  vacuo,  the 
blood  coagulates  quickly  ;  but  Lister  thinks  that  the  rapidity  of 
the  process  is  due  to  the  bubbling  which  ensues  from  the  escape 
of  gas,  and  to  the  blood  being  thus  brought  more  freely  into  con- 
tact with  the  containing  vessel. 

8.  The  coagulation  of  the  blood  is  prevented  altogether  by  the 
addition  of  strong  acids  and  caustic  alkalies. 

9.  It  has  been  believed,  and  chiefly  on  the  authority  of  Hunter, 
that  after  certain  modes  of  death  the  blood  does  not 
coagulate;  he  enumerates  the  death  by  lightning,  over-exertion 
(as  in  animals  hunted  to  death),   blows  on  the  stomach,   fits  of 


QO  THE    BLOOD.  [chap.  iv. 

anger.  He  says,  "  I  have  seen  instances  of  them  all."  Doubtless 
lie  had  done  so  ;  but  the  results  of  such  events  are  not  constant. 
The  blood  has  been  often  observed  coagulated  in  the  bodies  of 
animals  killed  by  lightning  or  an  electric  shock  ;  and  Gulliver  has 
published  instances  in  which  he  foundfclots  in  the  hearts  of  hares 
and  stags  hunted  to  death,  and  of  cocks  killed  in  fighting. 

Cause  of  the  fluidity  of  the  blood  within  the  living 
body. — Very  closely  connected  with  the  problem  of  the  coagula- 
tion of  the  blood  arises  the  question, — why  does  the  blood  remain 
liquid  within  the  living  body  ?  We  have  certain  pathological  and 
experimental  facts,  apparently'opposed  to  one  another,  which  bear 
upon  it,  and  these  may  be,  for  the  sake  of  clearness,  classed  under 
two  heads  : — 

(i)  Blood  will  coagulate  within  the  living  body  under  certain  con- 
ditions,— for  example,  on  ligaturing  an  artery,  whereby  the  inner 
and  middle  coats  are  generally  ruptured,  a  clot  will  form  within 
it,  or  by  passing  a  needle  through  the  coats  of  the  vessel  into  the 
blood  stream  a  clot  will  gradually  form  upon  it.  Other  foreign 
bodies,  e.g.  wire,  thread,  etc.,  produce  the  same  effect  It  is  a  well- 
known  fact  that  small  clots  are  apt  to  form  upon  the  roughened 
edges  of  the  valves  of  the  heart  when  the  roughness  has  been  pro- 
duced by  inflammation,  as  in  endocarditis,  and  it  is  also  equally 
true  that  aneurisms  of  arteries  are  sometimes  spontaneously  cured 
by  the  deposition  within  them,  layer  by  layer,  of  fibrin  from 
the  blood  stream,  which  natural  cure  it  is  the  aim  of  the  physician 
or  surgeon  to  imitate. 

(2)  Blood  will  remain  liquid  under  certain  conditions  outside  the 
body,  Avithout  the  addition  of  any  re-agent,  even  if  exposed  to  the 
air  at  the  ordinary  temperature.  It  is  well  known  that  blood 
remains  fluid  in  the  body  for  some  time  after  death,  and  it  is  only 
after  rigor  mortis  has  occurred  that  the  blood  is  found  clotted.  It  has 
been  demonstrated  by  Hewson,  and  also  by  Lister,  that  if  a  large 
vein  in  the  horse  or  iimilar  animal  be  ligatured  in  two  places  some 
inches  apart,  and  after  some  time  be  opened,  the  blood  contained 
within  it  will  be  found  fluid,  and  that  coagulation  will  occur  only 
after  a  considerable  time.  But  this  is  not  due  to  occlusion  from, 
the  air  simply.  Lister  further  showed  that  if  the  vein  with  the 
blood  contained  within  it  be  removed  from  the  body,  and  then  be 
carefully  opened,  the  blood  might  be  poured  from  the  vein  into 


chap,  iv.]  LGULATION. 


91 


another  similarly  prepared,  as  from  one  test-tube  into  anol 
thereby  Buffering  free  exposure  to  the  air,  without  coagulation 
occurring  as  long  as  the  vessels  retain  their  vitality,  [fthe  • 
theliol  lining  of  the  vein,  however,  be  injured,  the  blood  will  oot 
remain  liquid.  Again,  blood  will  remain  liquid  for  days  in  the 
heart  of  a  turtle,  which  continues  to  beat  for  a  very  Long  time 
after  removal  from  the  body. 

Any  theory  which  aims  at  explaining  the  fluidity  under  the 
usual  conditions  of  the  blond  within  the  Living  body  must  reconcile 
the  above  apparently  contradictory  facts,  and  must  at  the  same 
time  be  made  to  include  all  the  other  known  facts  concerning  the 
coagulation  of  the  blood.  We  may  therefore  dismiss  as  insufficient 
the  following  : — that  coagulation  is  due  to  exposure  to  the  air  or 
oxygen  ;  that  it  is  due  to  the  cessation  of  the  circulatory  move- 
ment j  that  it  is  due  to  evolution  of  various  gases,  or  to  the  loss 
of  heat. 

Two  theories,  those  of  Lister  and  Briicke,  remain.  The  former 
supposes  that  the  blood  has  no  natural  tendency  to  clot,  but  that 
its  coagulation  out  of  the  body  is  due  to  the  action  of  foreign 
matter  with  which  it  happens  to  be  brought  into  contact,  and  in 
the  body  to  conditions  of  the  tissues  which  cause  them  to  act 
towards  it  like  foreign  matter.  The  latter,  on  the  other  hand, 
supposes  that  there  is  a  natural  tendency  on  the  part  of  the  blood 
to  clot,  but  that  this  is  restrained  in  the  living  body  by  some 
inhibitory  power  resident  in  the  walls  of  the  containing  vessels. 

Support  was  once  thought  to  be  given  to  Briicke's  and  like 
theories  by  cases  of  injury,  in  which  blood  extravasated  in  the 
living  body  has  seemed  to  remain  uncoagulated  for  weeks,  or  even 
months,  on  account  of  its  contact  with  living  tissues.  But  the 
supposed  facts  have  been  shown  to  be  without  foundation.  The 
blood-like  fluid  in  such  cases  is  not  uncoagulated  blood,  but  a 
mixture  of  serum  and  blood-corpuscles,  with  a  certain  proportion 
of  clot  in  various  stages  of  disintegration     (Morrant  Baker.) 

As  the  blood  must  contain  the  substances  from  which  fibrin 
is  formed,  and  as  the  re-arrangement  of  these  substances  occurs 
very  quickly  whenever  the  blood  is  shed,  so  that  it  is  somewhat 
difficult  to  prevent  coagulation,  it  seems  more  reasonable  to  hold 
with  Briicke,  that  the  blood  has  a  strong  tendency  to  clot,  rather 
than  with  Lister,  that  it  ha-  ecial  tendency  thereto. 


t)2  THE    BLOOD.  [chap.  iv. 

It  has  been  recently  suggested  that  the  reason  why  blood  does 
not  coagulate  in  the  living  vessels,  is  that  the  factors  which  Ave 
have  seen  are  necessary  for  the  formation  of  fibrin  are  not  in  the 
exact  state  required  for  its  production,  and  that  the  fibrin  ferment 
is  not  formed  or  is  not,  at  any  rate,  free  in  the  living  blood,  but  that 
it  is  produced  (or  set  free)  at  the  moment  of  coagulation  by  the 
disintegration  of  the  colourless  corpuscles.  This  supposition  is 
certainly  plausible,  but  if  it  be  a  true  one,  it  must  be  assumed 
either  that  the  living  blood-vessels  exert  a  restraining  influence 
upon  the  disintegration  of  the  corpuscles  in  sufficient  numbers  to 
form  a  clot,  or  that  they  render  inert  any  small  amount  of  fibrin 
ferment  which  may  have  been  set  free  by  the  disintegration  of  a  few 
corpuscles ;  as  it  is  certain  that  corpuscles  of  all  kinds  must  from 
time  to  time  disintegrate  in  the  blood  without  causing  it  to  clot ; 
and,  secondly,  that  shed  and  defibrinated  blood  which  contains 
blood  corpuscles,  broken  down  and  disintegrated,  will  not,  when 
injected  into  the  vessels  of  an  animal,  produce  clotting.  There 
must  be  a  distinct  difference,  therefore,  if  only  in  amount,  between 
the  normal  disintegration  of  a  few  colourless  corpuscles  in  the 
living  uninjured  blood  vessels  and  the  abnormal  disintegration  of 
a  large  number  which  occurs  whenever  the  blood  is  shed  without 
suitable  precaution,  or  when  coagulation  is  unrestrained  by  the 
neighbourhood  of  the  living  uninjured  blood  vessels. 


The  Blood  Corpuscles  or  Blood-Cells. 

There  are  two  principal  forms  of  corpuscles,  the  red  and  the 
white,  or,  as  they  are  now  frequently  named,  the  coloured  and 
the  colourless.  In  the  moist  state,  the  red  corpuscles  form  about 
45  per  cent,  by  weight,  of  the  whole  mass  of  the  blood.  The 
proportion  of  colourless  corpuscles  is  only  as  i  to  500  or  600  of 
the  coloured. 

Red  or  Coloured  Corpuscles. — Human  red  blood-corpuscles 
are  circular,  biconcave  disks  with  rounded  edges,  from  ^Vo  to 
__i__  inch  in  diameter,  and  xyJoo  nicU  m  thickness,  becoming  flat 
or  convex  on  addition  of  water.  When  viewed  singly,  they  appear 
of  a  pale  yellowish  tinge;  the  deep  red  colour  which  they  give  to 
the  blood  being  observable  in  them  only  when  they  are  seen  en  masse. 


CHAP.   IV.  ] 


BLOOD-CORPUSI  I.l>. 


They  are  composed  of  a  colourless,  structureless,  and  transparent 
filmy  framework  or  stroma,  infiltrated  in  all  parts  bya  red  « -<  -1*  »m  i-ii  j — 
matter  termed  haemoglobin.  The  stroma  is  tough  and  elasl 
that,  as  the  cells  circulate,  they  admit  of  elongation  and  other 
changes  of  form,  in  adaptation  to  the  vessels,  yet  recover  their 
natural  Bhape  as  soon  as  they  escape  from  compression  The 
term  cell,  in  the  sense  of  a  bag  or  sac,  is  inapplicable  to  the  red 
blood  corpuscle  :  and  it  must  be  considered,  if  not  solid  through- 
out, yet  as  having  no  such  variety  of  consistence  in  different  parts 
as  to  justify  the  notion  of  its  being  a  membranous  sac  with  fluid 
contents.  The  stroma  exists  in  all  parts  of  its  substance,  and 
the  colouring-matter  uniformly  pervades  this,  and  is  not  merely 
surrounded  by  and  mechanically  enclosed  within  the  outer  wall  of 
the  corpuscle.  The  red  corpuscles  have  no  nuclei,  although,  in 
their  usual  state,  the  unequal  refraction  of  transmitted  light  giv<  - 
the  appearance  of  a  central  spot,  brighter  or  darker  than  the 
border,  according  as  it  is  viewed  in  or  out  of  focus.  Their  specific 
gravity  is  about  1088. 

Varieties. —  The  red  corpuscles  are  not  all  alike,  some  being 
rather  larger,   paler,    and    less    regular   than    the    majority,  and 


Fig.  6v  At  ",  ".  are  two  whi* 


sometimes  flat  or  slightly  convex,  with  a  shining  particle  apparent 
like    a   nucleolus.       In  almost  every    specimen   of   Mood   may   Ik- 


94 


THE    BLOOD.  [chap,  iv 


also  observed  a  certain  number  of  corpuscles  smaller  than  the 
rest.  They  are  termed  microeytes,  and  are  probably  immature 
corpuscles. 

A  peculiar  property  of  the  red  corpuscles,  exaggerated  in  inflam- 
matory blood,  may  be  here  again  noticed,  i.e.,  their  great  tendency 
to  adhere  together  in  rolls  or  columns,  like  piles  of  coins.  These 
rolls  quickly  fasten  together  by  their  ends,  and  cluster ;  so  that, 
when  the  blood  is  spread  out  thinly  on  a  glass,  they  form  a  kind  of 
irregular  network,  with  crowds  of  corpuscles  at  the  several  points 
corresponding  with  the  knots  of  the  net  (fig.  68).  Hence,  the  clot 
formed  in  such  a  thin  layer  of  blood  looks  mottled  with  blotches 
of  pink  upon  a  white  ground,  and  in  a  larger  quantity  of  such 
blood  help,  by  the  consequent  rapid  subsidence  of  the  corpuscles, 
in  the  formation  of  the  buffy  coat  already  referred  to. 

This  tendency  on  the  part  of  the  red  corpuscles,  to  form 
rouleaux,  is  probably  only  a  physical  phenomenon,  comparable 
to  the  collection  into  somewhat  similar  rouleaux  of  discs  of  corks 
when  they  are  partially  immersed  in  water.     (Norris.) 

Action  of  Reagents. — Considerable  light  has  been  thrown  on 
the  physical  and  chemical  constitution  of  red  blood-cells  by  study- 
ing the  effects  produced  hy  mechanical  means  and  by  various 
reagents  :  the  following  is  a  brief  summary  of  these  reactions  : — 

Pressure. — If  the  red  blood-cells  of  a  frog  or  man  are  gently 
squeezed,  they  exhibit  a  wrinkling  of  the  surface,  which  clearly 
indicates  that  there  is  a  superficial  pellicle  partly  differentiated 
from  the  softer  mass  within  ;  again,  if  a  needle  be  rapidly  drawn 
across  a  drop  of  blood,  several  corpuscles  will  be  found  cut  in  two, 
but  this  is  not  accompanied  by  any  escape  of  cell  contents ;  the 
two  halves,  on  the  contrary,  assume  a  rounded  form,  proving 
clearly  that  the  corpuscles  are  not  mere  membranous  sacs  with 
fluid  contents  like  fat-cells. 

Fluids. —  Water. — When  water  is  added  gradually  to  frog's 
blood,  the  oval  disc-shaped  corpuscles  become  spherical,  and 
gradually  discharge  their  hsemoglobin,  a  pale,  transparent  stroma 
beinc  left  behind  ;  human  red  blood-cells  change  from  a  discoidal 
to  a  spheroidal  form,  and  discharge  their  cell-contents,  becoming 
quite  transparent  and  all  but  invisible. 

Saline  solution  (dilute)  produces  no  appreciable  effect  on  the 


CHAP.  IV.] 


Tin:    COLOURED    CORPUSCLES 


95 


Mammal*.       Birds.  Re]  til.-s. 


Amphibia. 


Fish. 


Fig.  69. 


*  The  above  illustration  is  some  what  altered  from  a  drawing  by  Gulliver, 
in  the  Proceed.  Z00L  Societv,  and  exhibits  the  typical  characters  of  the  red 
blood-cells  in  the  main  divisions  of  the  Yertebrata.  The  fractions  are  these 
of  an  inch,  and  represent  the  average  diameter.  In  the  case  of  the  oval 
cells,  only  the  long  diameter  is  here  given.  It  is  remarkable,  that  although 
the  size  of  the  red  blood-cells  varies  so  much  in  the  different  classes  of  the 
vertebrate  kingdom,  that  of  the  white  corpuscles  remains  comparatively 
uniform,  and  thus  they  are,  in  some  animals,  much  greater,  in  others  much 
less  than  the  red  corpuscles  existing  side  by  side  with  them. 


96  THE    BLOOD.  [chap.  iv. 

red   blood-cells    of  the    fr<  _        In    the    red    blood-cells    of    man 

the  discoid  shape  is  exchanged  for  a  spherical  one,  with 
s&  £$      spinous  projections,  like  a  horse-chestnut  (fig.  70).     Their 
"^iv       original  forms    can    be    at    once   restored  by  the   use   of 
Fig-.  70.      carbonic  acid. 

Acetic  acid  (dilute)  causes  the  nucleus  of  the  red  blood 
cells  in  the  frog  to  become  more  clearly  defined  ;  if  the  action  is 
prolonged,  the  nucleus  becomes  strongly  granulated,  and  all   the 
colouring    matter   seems  to    be    concentrated   in   it,   the 
Burrounding  cell-substance  and  outline  of  the  cell  becom- 
ing almost   invisible  :    after  a  time  the  cells   lose  their 
colour  altogether.     The  cells  in  the  figure  (fig.  71 )  repre- 
sent the  successive  stages  of  the  change.     A  similar  loss 
of  colour  occurs  in  the  red  cells  of  human  blood,  which, 
however,  from  the  absence  of  nuclei,  seem  to  disappear  entirely. 
Alkalies  cause  the  red  blood-cells  to  swell  and  finally  disappear. 
Chloroform  added  to  the  red  blood-cells  of  the  frog  causes  them 
to  part  with  their  haemoglobin  ;  the  stroma  of  the  cells  becomes 
gradually  broken  up.     A  similar  effect  is  produced  on  the  human 
red  blood  cell. 

Tannin. — When  a  2  per  cent,  solution  of  tannic  acid  is  applied 
to  frog's  blood  it  causes  the  appearance  of  a  sharply-defined  little 
knob,  projecting  from  the  free  surface :  the 
colouring  matter  becomes  at  the  same  time 
concentrated  in  the  nucleus,  which  grows  more 
distinct  (fig.  72).  A  somewhat  similar  effect  i- 
produced  on  the  human  red  blood-cell.  (Robeit^.  | 
Magenta,  when  applied  to  the  red  blood-cells  of 
the  frog,  produces  a  similar  little  knob  or  knobs,  at  the  same 
time  staining  the  nucleus  and  causing  the  discharge  of  the 
haemoglobin.  (Roberts.)  The  first  effect  of  the  magenta  is  to 
cause  the  discharge  of  the  haemoglobin,  then  the  nucleus  becomes 
suddenly  stained,  and  lastly  a  finely  granular  matter  issues 
through  the  wall  of  the  corpuscle,  becoming  stained  by  the 
magenta,  and  a  macula  is  formed  at  the  point  of  escape.  A 
similar  macula  is  produced  in  the  human  red  blood-cell. 

Boracic  arid.- — A  2  per  cent,  solution  applied  to  nucleated 
blood-cells  (frog)  will  cause  the  concentration  of  all  the  colouring 
matter  in  the  nucleus  :  the  coloured  body  thus  formed  gradually 


chap.  iv.  1  ACTION    OF    REAGENTS.  gy 

quits    its   central    position,  and  comes   to  be  partly,  sometimes 
entirely   protruded    from    the  surface  of  the  now 

colourless  cell  (fig.  73).     The  result  of  this  experi- 
ment led  Briicke  to  distinguish  the  coloured   con- 
tents of  the  cell  (zooid)  from  its  colourless  stroma  Fi 
(oocoid).       When     applied    to    the    non-nucleated 
mammalian  corpuscle   its   effect   merely  resembles   that   of  other 
dilute  acids. 

Gases — Carbonic  acid. — If  the  red  blood-cells  of  a  frog  be  first 
exposed  to  the  action  of  water-vapour  (which  renders 
their  outer  pellicle  more  readily  permeable  to  gases),  and 
then  acted  on  by  carbonic  acid,  the  nuclei  immediately 
become  clearly  defined  and  strongly  granulated ;  when 
air  or  oxygen  is  admitted  the  original  appearance  is 
at  once  restored.  The  upper  and  lower  cell  in  fig.  74 
show  the  effect  of  carbonic  acid  ;  the  middle  one  the  effect  of 
the  re-admission  of  air.  These  effects  can  be  reproduced  five 
or  six  times  in  succession.  If,  however,  the  action  of  the  carbonic 
acid  be  much  prolonged,  the  granulation  of  the  nucleus  becomes 
permanent ;  it  appears  to  depend  on  a  coagulation  of  the  para- 
globulin.     (Strieker.) 

Ammonia. — Its  effects  seem  to  vary  according  to  the  degree  of 
concentration.  Sometimes  the  outline  of  the  corpuscles  becomes 
distinctly  crenated ;  at  other  times  the  effect  resembles  that  of 
boracic  acid,  while  in  other  cases  the  edges  of  the  corpuscles  begin 
to  break  up.     (Lankester.) 

Heat— The  effect    of  heat  up  to   1200— 1400  F.  (5oc— 6o°  C.) 
is  to  cause  the  formation  of  a  number  of  bud-like 
processes  (fig.  75).  <j»    © 

Electricity   causes    the    red    blood-corpuscles    to  ««  *  ~ 

become    crenated,    and    at    length    mulberry-like. 
Finally  they  recover  their  round  form  and  become  ^s-  75- 

quite  pale. 

The  general  conclusions  to  be  drawn  from  these  observations 
have  been  summed  up  as  follows  by  Prof.  Ray  Lankester  : — 

"The  red  blood-corpuscle  of  the  vertebrata  is  a  viscid,  and  at  the 
same  time  elastic  disc,  oval  or  round  in  outline,  its  surface  being 
differentiated  somewhat  from  the  underlying  material,  and  forming 
a  pellicle  or  membrane  of  great  tenuity,  not  distinguishable  with 

H 


98 


THE    BLOOD*  .  [chap,  iv. 


the  highest  powers  (whilst  the  corpuscle  is  normal  and  living),  and 
having  no  pronounced  inner  limitation.     The  viscid  mass  consists 
of  (or  rather  yields,  since  the  state  of  combination  of 
the  components  is  not  known)  a  variety  of  albuminoid 
and  other  bodies,  the  most  easily  separable  of  which 
is  haemoglobin ;  secondly,  the  matter  which  segregates 
Efg776.         to  form   Roberts's  macula ;   and   thirdly,  a  residuary 
stroma,    apparently   homogeneous   in    the   mammalia 
(excepting  as  far  as  the  outer  surface  or   pellicle  may  be  of  a 
different  chemical  nature),  but  containing  in  the  other  vertebrata 
a  sharply  definable  nucleus,  this  nucleus  being  already  differen- 
tiated, but  not  sharply  delineated  during  life,  and  consisting  of, 
or  separable  into)  at  least   two    components,  one  (paraglobulin) 
precipitable  by  carbon  dioxide,  and  removable  by  the  action  of 
weak  ammonia ;  the  other  pellucid,  and  not  granulated  by  acids." 
The   White    or    Colourless    Corpuscles. — In  human  blood 
the  white  or  colourless  corpuscles  or  leucocytes  are  nearly  spherical 
masses  of  granular  protoplasm  without  cell  wall.     The  granular 
appearance  more  marked  in  some  than  in  others  (vide  infra),  is 
due  to  the  presence  of  particles  probably  of  a  fatty  nature.     In  all 
cases  one  or  more  nuclei  exist  in  each  corpuscle.     The  size  of  the 
corpuscle  averages  Ywo  °f  an  incn  m  diameter, 

In  health,  the  proportion  of  white  to  red  corpuscles,  which, 
taking  an  average,  is  about  i  to  500  or  600,  varies  considerably 
even  in  the  course  of  the  same  day.  The  variations  appear  to 
depend  chiefty  on  the  amount  and  probably  also  on  the  kind  of 
food  taken  ;  the  number  of  leucocytes  being  very  considerably 
increased  by  a  meal,  and  diminished  again  on  fasting.  Also  in 
young  persons,  during  pregnancy,  and  after  great  loss  of  blood, 
there  is  a  larger  proportion  of  colourless  blood-corpuscles,  which 
probably  shows  that  they  are  more  rapidly  formed  under  these 
circumstances.  In  old  age,  on  the  other  hand,  their  proportion 
is  diminished. 

Varieties.— The  colourless  corpuscles  present  greater  diversi- 
ties of  form  than  the  red  ones  do.  Two  chief  varieties  are  to  be 
seen  in  human  blood  ;  one  which  contains  a  considerable  number 
of  granules,  and  the  other  which  is  paler  and  less  granular.  In 
size  the  variations  are  great,  for  in  most  specimens  of  blood  it  is 
possible   to  make   out,  in  addition  to  he    full-sized  varieties,    a 


i  hai-.  iv.]         WHITE    OB    COLOUBLE8S    I  OR] 


99 


Fig 


number   of  smaller   corpuscles,    <  •  •  ■  1 1  -  i  - 1  i  1 1  _r   ol 
nucleus  surrounded  by  a  variable  amount  of  more  or  L<  -  granular 
protoplasm.      The  small   corpuscl  -         .   in   all   probability,  the 
nndeyeloped  forma  of  the  others,  and  are  deriv< 
from  the  cella  of  the  lymph.     B  the  above- 

mentioned    vari<  •    3,    Schmidt    «!•  -  another 

form  which  he  l«-"ks  upon  as  intermediate  between 
the  coloured  and  the  colourless  forms,  viz.,  certain 
corpuscles  which  contain  red  granules  of  haemo- 
globin in  their  protoplasm.  The  different  varieties 
of  colourless  corpuscles  are  especially  well  seen  in 
the  1>1< '<•«!  of  frogs,  newts,  and  other  cold-blooded 
animals. 

Amoeboid  movement.— A  remarkable  property 
of  the  colourless  corpuscles  consists  in  their  capa- 
bility of  spontaneously  changing  their  shape.    This 

-  first  demonstrated  by  Wharton  Jones  in  the 
1  •!<  ■<  .«1  of  the  skate.  If  a  drop  of  blood  be  examined 
with  a  high  power  "f  the  microscope  on  a  warm 
ji    _•.',  or,  in  other  words,  under  conditions  by  which 

»  of  moisture  is  prevented,  and  at  the  same  time 
the  temperature  is  maintained  at  about  that  of  the 
blood  in  its  natural  state  within  the  walls  of  the 
living  oo"'  F.  (37'8C  C),  the  colourless  corpuscles  will  be 

rved  slowly  altering  their  shapes,  and  sending  out  pro., 
at  various  pans  of  their  circumference.     This  alteration  of  shape, 
which  can  be  m  nveniently  studied  in  the  newt's  blood,  is 

called  amoeboid,  inasmuch  as  it  strongly  resembles  the  movement 
of  the  lowly  organized  amoeba.     The  |         nes  which  are  sent  out 
are  either  lengthened  or  withdrawn.      If  lengthened,  the  proto- 
plasm of  the  whole   corpuscle  flows  as  it   were  into  its   pr 
and  the  corpuscle  chang   a  to   position;  if  withdrawn,  protr 
of  another  process  at  a  different  point  of  the  circumference  speedily 
follows.     The  change   of  position  of  the  corpuscle  can  also  take 
place  by  a  flowing  movement  of  the  whole  mass,  and  in  this 
the  locomotion  is  comparatively  rapid.     The  activity  both  in  the 
processes  of  change  of  shape  and  also  of  change   in   position,  is 
much  more  marked  in  some  corpuscles,  viz..  in  the  granular  variety 
than  in  others.     Klein  states  that  in  the  newt's  blood  the  changes 

H    2 


Thrre 
'.  hlood-r.or- 
B.  Thrt' 
hlood- 
rorpuscUs  acted 
on  by  acetic  acid ; 
the  nuclei  are 
very  clearly 
ble.     x  900. 


IOO  THE    BLOOD.  [chap.  iv. 

are  especially  likely  to  occur  in  a  variety  of  the  colourless  corpuscle, 
which  consists  of  masses  of  finely  granular  protoplasm  with  jagged 
outline,  containing  three  or  four  nuclei,  or  of  Large  irregular  masses 


Fig.  78. —  "Human  colourless  blood-corpuscle,  showing  its  successive  changes  of  outline  within 
ten  minutes  when  kept  moist  on  a  warm  stage.     (Schotield.) 

of  protoplasm  containing  from  five  to  twenty  nuclei.  Another 
phenomenon  may  he  observed  in  such  a  specimen  of  blood, 
viz.,  the  division  of  the  corpuscles,  which  occurs  in  the  following 
way.  A  cleft  takes  place  in  the  protoplasm  at  one  point,  which 
becomes  deeper  and  deeper,  and  then  by  the  lengthening  out  and 
attenuation  of  the  connection,  and  finally  by  its  rupture,  two  cor- 
puscles result.  The  nuclei  have  previously  undergone  division. 
The  cells  so  formed  are  said  to  be  remarkably  active  in  their  move- 
ments. Thus  we  see  that  the  rounded  form  which  the  colourless 
corpuscles  present  in  ordinary  microscopic  specimens  must  be 
looked  upon  as  the  shape  natural  to  a  dead  corpuscle  or  to  one 
whose  vitality  is  dormant  rather  than  as  the  shape  proper  to  one 
living  and  active. 

Action  of  re-agents  upon  the  colourless  corpuscles.— 
Feeding  the  coiyuscles. — If  some  fine  pigment  granules,  e.g.,  powdered 
vermilion,  be  added  to  a  fluid  containing  colourless  blood-cor- 
puscles, on  a  glass  slide,  these  will  be  observed,  under  the  micro- 
scope, to  take  up  the  pigment.  In  some  cases  colourless  corpuscles 
have  been  seen  with  fragments  of  coloured  ones  thus  embedded  in 
their  substance.  This  property  of  the  colourless  corpuscles  is 
especially  interesting  as  helping  still  further  to  connect  them  with 
the  lowest  forms  of  animal  life,  and  to  connect  both  with  the 
organized  cells  of  which  the  higher  animals  are  composed. 

The  property  which  the  colourless  corpuscles  possess  of  passing 
through  the  walls  of  the  blood-vessels  will  be  described  later  on. 

Enumeration  of  the  Red  and  White  Corpuscles. — Several 
methods  are  employed  for  pounting  the  blood-corpuscles,  most  of 
them  depending,  upon  the  same  principle,  i.e.,  the  dilution  of  a 
minute  volume  of  blood  with  a  given  volume  of  a  colourless  solution 
similar  in  specific  gravity  to  blood  serum,  so  that  the  size  and  shape 


'  II  \ 


I        ENUMERATION    OF    THE    CORPUS* 


IOI 


of  the  corpuscles  is  altered  as  little  as  possible.  A  minute 
quantity  of  the  well-mixed  solution  is  theo  taken,  examined 
under  the  mien  -  ther  in  a  flattened  capillary  tube  I  M.il 

or  in  a  cell  (Hayem  &  Nachet,  G  of  known  capacity,  and 

the  number  of  corpuscles  in  a  measured  length  of  the  tul 

_  ven   area  of  the  cell  is  counted.      The  Length  of  the   tube 
and  the  area  of  the  cell  are  ascertained  by  means  of  a  micron 
scale  in  the  microsc  Jar  ;  or  in  the  i    -  vers1  modifi- 


Fig.  79. — Ham' 

cation,   by   the  division  of  the   eell   area   into  squares  of  known 

size.     Having  ascertained  the  number  of  corpuscles  in  the  diluted 

1.    it    is   easy    to    rind    out  the  number  in  a  given    volume 

of  normal   blood.      Growers'  modification  of  Havem   &  Nachetfs 

■ 

instrument,   called  by   him  u Hccmacytomrter"  appears  to  be  the 

most  convenient  form  of  instrument  for  counting  the  cor- 
puscles, and  as  such  will  alone  be  described  (fig.  79).  It  consists 
of  a  small  pipette  (a),  which,  when  filled  up  to  a  mark  on  its 
stem,  holds  995  cubic  millimetres.  It  is  furnished  with  an  india- 
rubber  tube  and  glass  mouth-piece  to  facilitate  filling  and  empty- 
a  capillary  tube  (b)  marked  to  hold  5  cubic  millimetres,  and 


102  THE    BLOOD.  [chap.  iv. 

also  furnished  with  an  india-rubber  tube  and  mouthpiece ;  a  small 
glass  jar  (d)  in  which  the  dilution  of  the  blood  is  performed ;  a 
glass  stirrer  (e)  for  mixing  the  blood  thoroughly,  (f)  a  needle, 
the  length  of  which  can  be  regulated  by  a  screw  ;  a  brass  stage 
plate  (c)  carrying  a  glass  slide,  on  which  is  a  cell  one-fifth  of 
a  millimetre  deep,  and  the  bottom  of  which  is  divided  into  one- 
tenth  millimetre  squares.  On  the  top  of  the  cell  rests  the  cover 
glass,  which  is  kept  in  its  place  by  the  pressure  of  two  springs 
proceeding  from  the  stage  plate.  A  standard  saline  solution  of 
sodium  sulphate,  or  similar  salt,  of  specific  gravity,  1025  is  made, 
and  995  cubic  millimetres  are  measured  by  means  of  the  pipette 
into  the  glass  jar,  and  with  this  five  cubic  millimetres  of  blood, 
obtained  by  pricking  the  finger  with  a  needle,  and  measured 
in  the  capillary  pipette  (b),  are  thoroughly  mixed  by  the  glass 
stirring-rod.  A  drop  of  this  diluted  blood  is  then  placed  in  the 
cell  and  covered  with  a  cover-glass,  which  is  fixed  in  position  by 
means  of  the  two  lateral  springs.  The  preparation  is  then  ex- 
amined under  a  microscope  with  a  power  of  about  400  diameters, 
and  focussed  until  the  lines  dividing  the  cell  into  squares  are 
visible. 

After  a  short  delay,  the  red  corpuscles  which  have  sunk  to  the 
bottom  of  the  cell,  and  are  resting  on  the  squares,  are  counted  in 
ten  squares,  and  the  number  of  white  corpuscles  noted.  By 
adding  together  the  numbers  counted  in  ten  (one-tenth  milli- 
metre) squares  the  number  of  corpuscles  in  one-cubic  millimetre 
of  blood  is  obtained.  The  average  number  of  corpuscles  per  each 
cubic  millimetre  of  healthy  blood,  according  to  Yierordt  and 
Welcker,  is  5,000,000  in  adult  men,  and  rather  fewer  in  women. 

Chemical  Composition  of  the   Blood  in  Bulk. 

Water 784 

Solids- 
Corpuscles         130 

Proteids  (of  serum)      .        .                 .     .  70 

Fibrin  (of  clot) 2-2 

Fatty  matters  (of  senim)      .         .         .     .  1-4 

Inorganic  salts  (of  serum)         ...  6 
Gases,  kreatm,  urea  and  other  extractive  ) 

matter,   glucose  and    accidental   sub-  >  64. — 

stances '  216 

1,000 


chap.  iv. J  CHEMICAL    COMPOSITION.  203 

Chemical  Composition  of  the  Red  Corpuscles. — Anal 
of  a  thousand  parts  of  moist  blood  corpuscles  shows  the  following 

a^  the  result  : — 




Solid — 

I  Organic 303SS 

(  Mineral Si 2 — ^12 


1. 000 


Of  the  solids  the  most  important  is  Ha  ,  th     substance 

to  which  the  blood  owes  its  colour.     It  constitutes,  as  will  be  5 

from  the  appended  Table,  more  than  90  per  eeut.  of  the  organic 
matter  of  the  corpuscles.  Besides  haemoglobin  there  are  proteid  * 
and  fatty  matters,  the  former  chiefly  consisting  of  globulins,  and 
the  latter  of  eh      rt      n  and  lecithin. 

In  1000  parrs  organic  matter  are  found  : — 

Haemoglobin     ........    905*4 

Proteids 867 

F:"~ 7'9 


I.OOO' 


Of   the   inorganic  salts  of  the  corpuscles,  with   the  iron 
omitted — 

In  1000  pans  corpuscles  (Schmidt)  are  found  : — 


Potassium  Chloride 
Phosphate 
sulphate 

Sodium 

Calcium 
_nesium 


679 
343 

094 
060 
34i 


7'2&2 


The   properties   of  haemoglobin  will   be   considered   in  relation 
to  the  Gases  of  the  blood. 


*  An  account  of  the  proteid  bodies,  kc,  will  be  found  in  the  Appendix,  an  I 
should  be  referred  to  for  explanation  of  the  terms  employed  in  the  text. 


104 


THE    BLOOD.  [chap,  iv, 


Chemical  Composition  of  the  Colourless  Corpuscles.— 
In  consequence  of  the  difficulty  of  obtaining  colourless  corpuscles 
in  sufficient  number  to  make  an  analysis,  little  is  accurately  known 
of  their  chemical  composition  ;  in  all  probability,  however,  the 
stroma  of  the  corpuscles  is  made  up  of  proteid  matter,  and  the 
nucleus  of  nuclein,  a  nitrogenous  phosphorus-containing  body 
akin  to  mucin,  capable  of  resisting  the  action  of  the  gastric  juice. 
The  proteid  matter  (globulin)  is  soluble  in  a  ten  per  cent,  solution 
of  sodium  chloride,  and  the  solution  is  precipitated  on  the  addition 
of  water,  by  heat  and  by  the  mineral  acids.  The  stroma  contains 
fatty  granules,  and  in  it  also  the  presence  of  glycogen  has  been 
demonstrated.  The  salts  of  the  corpuscles  are  chiefly  potassium, 
and  of  these  the  phosphate  is  in  greatest  amount. 

Chemical  Composition  of  the  Plasma  or  Liquor  Sanguinis. 
— The  liquid  part  of  the  blood,  the  plasma  or  liquor  sanguinis  in 
which  the  corpuscles  float,  may  be  obtained  in  the  ways  mentioned 
under  the  head  of  the  Coagulation  of  the  Blood.  In  it  are  the 
fibrin  factors,  inasmuch  as  when  exposed  to  the  ordinary  tem- 
perature of  the  air  it  undergoes  coagulation  and  splits  up  into 
fibrin  and  serum.  It  differs  from  the  serum  in  containing 
fibrinogen,  but  in  appearance  and  in  reaction  it  closely  resembles 
that  fluid ;  its  alkalinity,  however,  is  less  than  that  of  the  senmi 
obtained  from  it.  It  may  be  freed  from  white  corpuscles  by 
filtration  at  a  temperature  below  410  F.  (5°C). 

Fibrin. — The  part  played  by  fibrin  in  the  formation  of  a  clot 
has  been  already  described  (p.  81),  and  it  is  only  necessary  to 
consider  here  its  general  properties.  It  is  a  stringy  elastic  sub- 
stance belonging  to  the  proteid  class  of  bodies.  It  i.s  insoluble 
in  water  and  in  weak  saline  solutions,  it  swells  up  into  a  trans- 
parent jelly  when  placed  in  dilute-hydrochloric  acid,  but  does  not 
dissolve,  but  in  strong  acid  it  dissolves,  producing  acid-albumin  *  ; 
it  is  also  soluble  on  boiling  in  strong  saline  solutions.  Blood 
contains  only  '2  per  cent,  of  fibrin.      It  can  be  converted  by  the 


*  The  use  of  the  two  words  albumen  and  albumin  may  need  explanation. 
The  former  is  the  generic  word,  which  may  include  several  albuminous  or 
proteid  bodies.  e.g.,  albumen  of  blood  ;  the  latter  which  requires  to  be 
qualified  by  another  word  is  the  specific  form,  and  is  applied  to  varieties, 
e.g.  egg-albumin,  serum-albumin. 


CHAP.   !V.J 


COMPOSITION    OF    SERUM. 


IO: 


r  pancreatic  jui         I    peptone.     It   \ 

of  liberating  the  oxygen  from   solutions  of  hydric  1 l< »  . 

Tins  may  be  Bhown  by  dipping  a  few  Bhreda  "f  rihrin  in  tincture 
laiacum  and  then  immersing  them  in  a  Bolntion  of  hydric 
ode.     The  fibrin  h<  bluish  colour,  from  its  haying 

liberated  from  the  solution         _  o,   which  oxidises  the  resin  of 

guaiacum  contained  in  tlie  tincture  and  thus  produces  the  © 


Salts  of  the  Plasma. — In  iooo  parts  plasma  tl 

Sodium  Chloride    ...... 

Soda 

Sodium   Phosphate        ..... 

Potassium  chloride      ...... 

sulpha:  ..... 

Icium  phosphate       ...... 

Magnesium  phosphate      ..... 


ere  are 

5-546 

1-532 

■271 

•359 
•281 
•298 
■218 


5S05 


Serum. — The  serum  is  the  liquid  part  of  the  blood  or  of  the 
plasma    remaining    after   t:       5       ration  of  the  clot      It    is 
alkaline,  yellowish,   transparent  fluid,  with   a   specific   gravity   of 
from  1025  to   1032.     In  the  usual  mode  of  coagulation, 

-■nun  remains  in  the  clot,  and  the  rest,  squeezed  from  the 

Lot  by  ite  contraction,  lies  around  it.  Since  the  contraction  of 
the  clot  may  continue  for  thirty-six  or  more  hours,  the  quantity 
of  serum  in  the  blood  cannot  be  even  roughly  estimated  till  this 
period  has  elapsed.     There  is  nearly  as  much,  by  weight,  of  serum 

-  there  ia  clot  in  coagulated  blood. 


Chemical  Composition  of  the  Serum. 


about     900 




Proteids  : 
a.  Serum-albumin  ..... 

&.  Paraglobulin        ......  J 

Salts. 

— including  fatty  adds,   eholesterin.   lecithin  ; 
and  some  soaps      ....... 

Grape  sugar  in  small  amount        ..... 

Kxtractives — kreatin.  kreatinin.  urea.  a:c. 

Yellow  pigment,  which  is  independent  of  haemoglobin 

Gases — small  amounts  of  oxygen,  nitrogen,  and  car- 
bonic acid     ........ 


So 


20 


I  coo 


106  THE    BLOOD.  [chap.  iv. 

Water. — The  water  of  the  serum  varies  in  amount  according 
to  the  amount  of  food,  drink,  and  exercise,  and  with  many  other 
circumstances. 

Proteids. — a.  Serum-albumin  is  the  chief  proteid  found  in 
serum. 

It  is  precipitated  on  heating  the  seruni  to  1400  F.  (6o°  C),  and  entirely 
coagulates  at  (1670  F.  75°  C),  and  also  by  the  addition  of  strong  acids, 
such  as  nitric  and  hydrochloric  ;  by  long  contact  with  alcohol  it  is  precipi- 
tated. It  is  not  precipitated  on  addition  of  ether,  and  so  differs  from  the 
other  native  albumin,  viz.,  <?//#-alburain.  "When  dried  at  1040  F.  (400  C.) 
serum-albumin  is  a  brittle,  yellowish  substance,  soluble  in  water,  possessing 
a  lasvo-rotary  power  of  —  560.  It  is  with  great  difficulty  freed  from  its 
salts,  and  is  precipitated  by  solutions  of  metallic  salts,  e.g.,  of  mercuric 
chloride,  copper  sulphate,  lead  acetate,  sodium  tungstate,  &c.  If  dried  at 
a  temperature  over  1670  F.  (750  C.)  the  residue  is  insoluble  in  water,  having 
been  changed  into  coagulated  proteid. 

(3.  Paraglobulin  can  be  obtained  as  a  white  precipitate  from 
cold  serum  by  adding  a  considerable  excess  of  water  and  passing 
through  it  a  current  of  carbonic  acid  gas  or  by  the  cautious 
addition  of  dilute  acetic  acid.  It  can  also  be  obtained  by  satu- 
rating serum  with  crystallized  sulphate  magnesium  or  chloride 
sodium.  "When  obtained  in  the  latter  way  precipitation  seems 
to  be  much  more  complete  than  by  means  of  the  former  method. 
Paraglobulin  belongs  to  the  class  of  proteids  called  globulins. 

The  proportion  of  serum-albumin  to  paraglobulin  in  human 
blood  serum  is  as  1*511  to  1. 

The  salts  of  sodium  predominate  in  serum  as  in  plasma,  and  of 
these  the  chloride  generally  forms  by  far  the  largest  proportion. 

Fats  are  present  partly  as  fatty  acids  and  partly  emulsified. 
The  fats  are  triolein,  iridearin,  and  tripalmitin.  The  amount 
of  fatty  matter  varies  according  to  the  time  after,  and  the  in- 
o-redients  of,  a  meal.  Of  cholesterin  and  lecithin  there  are  mere 
traces. 

Grape  sugar  is  found  principally  in  the  blood  of  the  hepatic- 
vein,  about  one  part  in  a  thousand. 

The  extractives  vary  from  time  to  time  ;  sometimes  uric  and 
hippuric  acids  are  found  in  addition  to  urea,  kreatin  and  krea- 
tinin.     Urea  exists  in  proportion  from  -02  to  -04  per  cent. 

The  yellow  pigment  of  the  serum  and  the  odorous  matter  which 


chap,  iv.]  VARIATIONS    I.v    COMPOSITION.  i0y 

gives  the  blood  of  each  particular  animal  a  peculiar  smell,  have 
not  yet  been  properly  isolated. 


Variations  in  healthy  Blood  nnder  different 
Circumstances. 

The  conditions  which  appear  most  to  influence  the  composition 
of  the  blood  in  health  are  these  :  Sex,  Pregnancy,  Age,  and  Tem- 
perament. The  composition  of  the  blood  is  also,  of  course,  much 
influenced  by  diet. 

i.  Sex. — The  blood  of  men  differs  from  that  of  women,  chiefly  in  being  of 
S'  ■niewhat  higher  specific  gravity,  from  its  containing  a  relatively  larger 
quantity  of  red  corpuscles. 

2.  Pregnancy. — The  blood  of  pregnant  women  has  a  rather  lower  specific 
gravity  than  the  average,  from  deficiency  of  red  corpuscles.  The  quantity 
of  white  corpuscle-,  on  the  other  hand,  and  of  fibrin,  is  increased. 

3.  Age. — It  appear-  that  the  blood  of  the  foetus  is  very  rich  in  solid 
matter,  and  especially  in  red  corpuscles  :  and  this  condition,  gradually 
diminishing,  continues  for  some  weeks  after  birth.  The  quantity  of  solid 
matter  then  falls  during  childhood  below  the  average,,  again  rises  during 
adult  life,  and  in  old  age  falls  again. 

4.  Temperament. — But  little  more  is  known  concerning  the  connection  of 
this  with  the  condition  of  the  blood,  than  that  there  appears  to  be  a  rela- 
tively larger  quantity  of  solid  matter,  and  particularly  of  red  corpuscles,  in 
those  of  a  plethoric  or  sanguineous  temperament. 

5.  Diet. — Such  differences  in  the  composition  of  the  blood  as  are  due  to 
the  temporary  presence  of  various  matters  absorbed  with  the  food  and  drink, 
as  well  as  the  more  lasting  changes  which  must  result  from  generous  or  poor 
diet  respectively,  need  be  here  only  referred  to. 

Effects  of  Bleeding. — The  result  of  bleeding  is  to  diminish  the  specific 
gravity  of  the  blood  ;  and  so  quickly,  that  in  a  single  venesection,  the  por- 
tion of  blood  last  drawn  has  often  a  less  specific  gravity  than  that  of  the 
blood  that  flowed  first.  This  is,  of  course,  due  to  absorption  of  fluid  from 
the  tissues  of  the  body.  The  physiological  import  of  this  fact,  namely,  the 
instant  ab-orption  of  liquid  from  the  tissues,  is  the  same  as  that  of  the 
intense  thirst  which  is  so  common  after  either  loss  of  blood,  or  the  abstraction 
from  it  of  watery  fluid,  as  in  cholera,  diabetes,  and  the  like. 

For  some  little  time  after  bleeding,  the  want  of  red  corpuscles  is  well 
marked  :  but  with  this  exception,  no  considerable  alteration  seems  to  be 
produced  in  the  composition  of  the  blood  for  more  than  a  very  short  time  : 
the  loss  of  the  other  constituents,  including  the  pale  corpuscles,  being  very 
quickly  repaired. 


108  THE    BLOOD.  [<  hai'.  iv. 


Variations  in  the  Composition   of  the  Blood,  in  different 

Parts  of  the  Body. 

The  composition  of  the  blood,  as  might  he  expected,  is  found  to 
vary  in  different  parts  of  the  body.  Thus  arterial  blood  differs 
from  venous  ;  and  although  its  composition  and  general  characters 
are  uniform  throughout  the  whole  course  of  the  systemic  arteries, 
they  are  not  so  throughout  the  venous  system, — the  blood  con- 
tained in  some  veins  differing  remarkably  from  that  in  others. 

Differ ences  between  Arterial  and  Venous  Blood. — The 
differences  between  arterial  and  venous  blood  are  these  : — 

(a.)  Arterial  blood  is  bright  red,  from  the  fact  that  almost  all 
its  hemoglobin  is  combined  with  oxygen  (Oxyhemoglobin,  or 
scarlet  haemoglobin),  while  the  purple  tint  of  venous  blood  is  due 
to  the  deoxidation  of  a  certain  quantity  of  its  oxyhemoglobin,  and 
its  consequent  reduction  to  the  purple  variety  (Deoxidised,  or 
purple  hemoglobin). 

(b.)  Arterial  blood  coagulates  somewhat  more  quickly. 

(c.)  Arterial  blood   contains  more  oxygen  than  venous,  and  less 

carbonic  acid. 

Some  of  the  veins  contain  blood  which  differs  from  the  ordinary 

standard  considerably.     These  are  the  Portal,  the  Hepatic,  and 

the  Splenic  veins. 

Portal  vein. — The  blood  which  the  portal  vein  conveys  to  the  liver  is 
supplied  from  two  chief  sources  ;  namely,  that  in  the  gastric  and  mesenteric 
veins,  which  contains  the  soluble  elements  of  food  absorbed  from  the  stomach 
and  intestines  during  digestion,  and  that  in  the  splenic  vein  ;  it  must,  there- 
fore, combine  the  qualities  of  the  blood  from  each  of  these  sources. 

The  blood  in  the  gastric  and  mesenteric  veins  will  vary  much  according 
to  the  stage  of  digestion  and  the  nature  of  the  food  taken,  and  can  therefore 
be  seldom  exactly  the  same.  Speaking  generally,  and  without  considering  the 
sugar,  dextrin,  and  other  soluble  matters  which  may  have  been  absorbed 
from  the  alimentary  canal,  this  blood  appears  to  be  deficient  in  solid  matters 
especially  in  red  corpuscles,  owing  to  dilution  by  the  quantity  of  water 
absorbed,  to  contain  an  excess  of  albumin,  and  to  yield  a  less  tenacious  kind 
of  fibrin  than  that  of  blood  generally. 

The  blood  from  the  splenic  vein  is  generally  deficient  in  red  corpuscles, 
and  contains  an  unusually  large  proportion  of  proteids.  The  fibrin  obtain- 
able from  the  blood  seems  to  vary  in  relative  amount,  but  to  be  almost  always 
above  the  average.  The  proportion  of  colourless  corpuscles  is  also  unusually 
large.  The  whole  quantity  of  solid  matter  is  decreased,  the  diminution 
appearing  to  be  chiefly  in  the  proportion  of  red  corpuscles. 


,  ii\r.  iv.  1  (.asks    OF    THE    BLOOD.  109 

The  blood  of  the  portal  vein,  combining  the  peculiarities  of  its  1  wo  factors, 
plenic  and  mesenteric  venous  blood,  is  usually  of  Lower  specific 
than  blood  generally,  is  more  watery,  contains  fewer  red  corpuscles,  more 
proteids,  and  yields  a  Less  firm  clol  than  thai  yielded  by  other  blood,  owing 
to  the  deficienl  tenacity  of  its  fibrin. 

Guarding  (by  ligature  of  the  portal  vein)  against  the  possibility  of  an 
error  in  the  analysis  from  regurgitation  of  hepatic  blood  into  the  portal 
rein,  recent  observers  have  determined  thai  hepatic  venous  "blood  contains 
lees  water,  albumen,  and  -alts,  than  the  blood  of  the  portal  vein  ;  but  thai 
it  yields  a  much  larger  amount  of  extinctive  matter,  in  which  is  one  con- 
Btanl  element,  namely,  grape-sugar,  which  is  found,  whether  Baccharine  01 
farinaceous  matter  have  beer  presenl  in  the  food  or  not. 


The  Gases  of  the  Blood. 

The  gases  contained  in  the  blood  are  Carbonic  acid,  Oxygen, 
and  Nitrogen,  100  volumes  of  blood  containing  from  50  to  60 
volumes  of  these  gases  collectively. 

Arterial  blood  contains  relatively  more  oxygen  and  less  carbonic 
acid  than  venous.  But  the  absolute  quantity  of  carbonic  acid  is 
in  both  kinds  of  blood  greater  than  that  of  the  oxygen. 

Oxygen.  Carbonic  Arid.  Nitrogen. 

Arterial  Blood  .         .         20  vol.  per  cent.  39  vol.  per  cent.  1  to  2  vols. 
Venous         „ 

(from  muscles  at  rest)    8  to  12     ..     ..       ..  46     l  to  2  v0^- 

The  Extraction  of  the  Gases  from  the  Blood. — As  the  ordinary  air- 
pumps  are  not  sufficiently  powerful  for  the  purpose,  the  extraction 
of  the  gases  from  the  blood  is  accomplished  by  means  of  a 
mercurial  air-pump,  of  which  there  are  many  varieties,  those  of 
Ludwig,  Alvergnidt,  Geissler,  and  Sprengel  being  the  chief.  The 
principle  of  action  in  all  is  much  the  same.  Ludwig's  pump, 
which  may  be  taken  as  a  type,  is  represented  in  the  figure.  It 
consists  of  two  fixed  glass  globes,  0  and  F,  the  upper  one  com- 
municating by  means  of  the  stopcock  D,  and  a  stout  india-rubber 
tube  with  another  glass  globe,  L,  which  can  be  raised  of  lowered 
by  means  of  a  pulley;  it  also  communicates  by  means  of  a  stop- 
cock, B,  and  a  bent  glass  tube,  A,  with  a  gas  receiver  (not  repre- 
sented in  the  figure),  A  dipping  into  a  bowl  of  mercury,  so  that 
the  gas  may  be  received  over  mercury.  The  lower  globe,  F, 
communicates  with  G  by  means  of  the  stopcock,  E,  with  /  in 
which  the   blood   is    contained   by  the  stopcock,   G,  and  with  a 


no 


THE    BLOOD. 


[chap.  IV. 


movable  glass  globe,  21,  similar  to  Z,  by  means  of  the  stopcock,  H, 
and  the  stout  india-rubber  tube,  K. 

In  order  to  work  the  pump,  L 
and  M  are  filled  with  mercury, 
the  blood  from  which  the  gases 
are  to  be  extracted  is  placed  in  the 
bulb  I,  the  stopcocks,  H,  E,  D, 
and  B,  being  open,  and  G  closed. 
M  is  raised  by  means  of  the  pulley 
until  F  is  full  of  mercury,  and 
the  air  is  driven  out.  E  is  then 
closed,  and  L  is  raised  so  that  C 
■mes  full  of  mercury,  and  the 
air  driven  off.  B  is  then  closed. 
On  lowering  L  the  mercury  runs 
into  it  from  C,  and  a  vacuum  is 
established  in  0.  On  opening  E 
and  lowering  J/,  a  vacuum  is 
similarly  established  in  F ;  if  G  be 
now  opened,  the  blood  in  I  will 
enter  into  ebullition,  and  the  gases 
will  pass  off  into  F  and  C,  and  on 
raising  M  and  then  L,  the  stop- 
cock B  being  opened,  the  gas  is 
driven  through  A,  and  is  received 
into  the  receiver  over  mercury. 
By  repeating  the  experiment  seve- 
ral times  the  whole  of  the  gases  of 
the  specimen  of  blood  is  obtained, 
and  may  be  estimated. 
The  Oxygen  of  the  Blood. — It  has  been  found  that  a  very 
small  proportion  of  the  oxygen  which  can  be  obtained,  by  the  aid 
of  the  mercurial  pump,  from  the  blood,  exists  in  a  state  of  simple 
solution  in  the  plasma.  If  the  gas  were  in  simple  solution,  the 
amount  of  oxygen  in  any  given  quantity  of  blood  exposed  to  any 
given  atmosphere  ought  to  vary  with  the  amount  of  oxygen  con- 
tained in  the  atmosphere.  Since,  speaking  generally,  the  amount 
of  any  gas  absorbed  by  a  liquid  such  as  plasma  would  depend 
upon  the  proportion  of  the  gas  in  the  atmosphere  to  which  the 


Tis. 


. — Luduriffs  Mercurial  Puhijk 


chap,  iv.]  GA8ES    OF    J  SE    BLOOD.  j  n 

liquid  w  aed — if  the  proportion  wea 

would  be  great  ;  if  small,  the  al  n  would  be  similarly  small 

The  absorption  would  continue  until  the  proportion  of  the  gas  in 
the  liquid  and  in  the  atmosphere  became  equal     other  things 

would,  of  .  influence  the  absorption,  such  as  tl 

employed,  natur*  .  and  tl.  f  both,  but 

the  amount  of      _  -  which  a  liquid  abs  ends 

upon  the  proportion  of  the  gas — the  so-called  partial  pressure — of 
_   -  in  the  atmosphere  t<>  which  the  liquid  is  subjected.     And 
conversely,  if  a  liquid  containing  a  gas  in  solution  be  exposed  to  an 
_  aoneofthe  gas,  the  gas  will  he  given  up  to 
the  atmosphere  until  its  amount  in  the  liquid  and  in  the  atmosphere 
equal.     This  condition  is  called  a  condition  of  equal  ten- 
The  condition  may  be  understood  by  a  simple  illustration. 
A  large  amount  of  carbonic  acid   gas  is    lissolved  in  a  bottle  of 
water  by  exposing  the  liquid  to  extreme  pressure  of  the  gas.  and 
a  cork  is  placed  in  the  bottle  and  wired  down.     The  gas  exists  in 
the  water  in  a  condition  of  extreme  tension,  and  therefore  there  is 
a  tendency  of  the  _   -  '      -.ape  into  the  atmosphere,  in  order  that 
the  tension  may  be  relieved  :  this  causes  the  violent  expulsion  of 
the  cork  when  the  wire  is  removed,  and  if  the  water  be  placed  in  a 
2     as  th(    gas  will  continue  to  be  evolved  until  it  U  st  all  got 

rid  of,  and  the  tension  of  the  gas  in  the  water  approximates  to  that 
of  the  atmosphere  in  which,  it  should  be  remembered,  the  carbon 
dioxide  is,  naturally,  in  very  small  amount,  viz.,  '04  per  cent. 
Now  the  oxygen  of  the  blood  does  not  obey  this  law  of  pressure. 
For  if  blood  which  contains  little  or  no  oxygen  be  exposed  * 
succession  of  atmospheres  containing  more  and  more  of  that  _  s, 
we  find  that  the  absorption  is  at  first  very  great,  but  soon  becomes 
relatively  very  small,  not  being  therefore  regularly  in  |  >n  to 

the  increased  amount  (or  tension)  of  the  oxygen  of  the  atmosph 
and  that  conversely,  if  arterial  blood  be  submitted  to  regularly 
diminishing  pressures  1  if  oxygen,  at  first  veiy  little  of  the  contained 
oxygen  is  uiven  off  to  the  atmosphere,  then  suddenly  the  _  - 
escapes  with  great  rapidity,  again  disobeying  the  law  of 
pressures. 

Very  little  oxygen  can  be  obtained  from  serum  freed  from  blood 
corpuscles,  even  by  the  strongest  mercurial  air-pump,  neither  can 
serum  be  made  to  absorb  a  large  quantity  of  that  gas  ;  but  the  small 


112 


THE    BLOOD.  [chai\  iv. 


quantity  which  is  so  given  up  or  so  absorbed  follows  the  laws  of 
absorption  according  to  pressure. 

It  must  be,  therefore,  evident  that  the  chief  part  of  the  oxygen 
is  contained  in  the  corpuscles,  and'  not  in  a  state  of  simple  solu- 
tion. The  chief  solid  constituent  of  the  coloured  corpuscles  is 
haemoglobin,  which  constitutes  more  than  90  per  cent,  of  their 
bulk.  This  body  has  a  very  remarkable  affinity  for  oxygen, 
absorbing  it  to  a  very  definite  extent  under  favourable  circum- 
stances, and  giving  it  up  when  subjected  to  the  action  of  reducing 
agents,  or  to  a  sufficiently  low  oxygen  pressure.  From  these  facts 
it  is  inferred  that  the  oxygen  of  the  blood  is  combined  with 
haemoglobin,  and  not  simply  dissolved ;  but  inasmuch  as  it  is 
comparatively  easy  to  cause  the  haemoglobin  to  give  up  its  oxygen, 
it  is  believed  that  the  oxygen  is  but  loosely  combined  with  the 
substance. 

Haemoglobin. — Haemoglobin  is  a  crystallizable  body  which 
constitutes  by  far  the  largest  portion  of  the  coloured  corpuscles. 
It  is  intimately  distributed  throughout  their  stroma,  and  must  be 
dissolved  out  of  it  before  it  will  undergo  crystallization.  Its 
percentage  composition  is  C.  53*85  ;  H.  7-32  ;  N.  16*17  \  0.  21*84; 
S.  -63  ;  Fe.  "42  ;  and  if  the  molecule  be  supposed  to  contain 
one  atom  of  iron  the  formula  would  be  C^,  H^,  NI54,  Fe  S3  0I79. 
The  most  interesting  of  the  properties  of  haemoglobin  are  its 
powers  of  crystallizing  and  its  attraction  for  oxygen  and  other 
gases. 

Crystals. — The  haemoglobin  of  the  blood  of  various  animals 
possesses  the  power  of  crystallizing  to  very  different  extents 
(blood-crystals).  In  some  animals  the  formation  of  crystals  is 
almost  spontaneous,  whereas  in  others  crystals  are  formed  either 
with  great  difficulty  or  not  at  all.  Among  the  animals  whose 
blood  colouring-matter  crystallizes  most  readily  are  the  guinea- 
pig,  rat,  squirrel,  and  dog  ;  and  in  these  cases  to  obtain  crystals 
it  is  generally  sufficient  to  dilute  a  drop  of  recently-drawn  blood 
with  water  and  expose  it  for  a  few  minutes  to  the  air.  Light 
seems  to  favour  the  formation  of  the  crystals.  In  many  instances 
other  means  must  be  adopted,  e.g.,  the  addition  of  alcohol,  ether, 
or  chloroform,  rapid  freezing,  and  then  thawing,  an  electric 
current,  a  temperature  of  1400  F.  (6o°  C),  or  the  addition  of 
sodium  sulphate. 


CJIA1'.    IV.] 


HEMOGLOBIN. 


113 


Human  blood  crystallizes  with  difficulty,  as  does  also  that  of  the 
ox.  the  pig,  the  sheep,  and  the  rabbit 


Tig.  81.— Crystals  of  oxy-hamoglobin— prismatic  from  human  blood. 

The  forms  of  haemoglobin  crystals,  as  will  be  seen  from  the 
appended  figures,  differ  greatly. 


* 


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'dral,  from  blood  of  the  guinea-pig. 


f  ^oodofsauu^eV:  On  these  hex*  - 
IS  plates,  prismatic  crystals,  grouped 
inT  stellate  manner,  not  unfrequently 
occur  [after  Funke  . 

Haemoglobin  crystals  are  soluble  in  water.  Both  the  crystals 
themselves  and  also  their  solutions  have  the  characteristic  colour 
of  arterial  blood. 


114  THE    BL00r)-  [chap.  iv. 

A  dilute  solution  of  haemoglobin  gives  a  characteristic  appear- 
ance with  the  spectroscope.  Two  absorption  bands  are  seen 
between  the  solar  lines  d  and  e  (see  plate),  one  towards  the  red, 
with  its  middle  line  some  little  way  to  the  blue  side  of  d,  is  very 
intense,  but  narrower  than  the  other,  which  lies  near  to  the  red 
side  of  e.  Each  band  is  darkest  in  the  middle  and  fades  away  at 
the  sides.  As  the  strength  of  the  solution  increases  the  bands 
become  broader  and  deeper,  and  both  the  red  and  the  blue  ends 
of  the  spectrum  become  encroached  upon  until  the  bands  coalesce 
to  form  one  very  broad  band,  and  only  a  slight  amount  of  the 
green  remains  unabsolved,  and  part  of  the  red,  and  on  further 
increase  of  strength  the  former  disappears. 

If  the  crystals  of  oxy-heemoglobin  be  subjected  to  a  mercurial 
air-pump  they  give  off  a  definite  amount  of  oxygen  (i  gramme 
giving  off  i*59  c.  cm.  of  oxygen),  and  they  become  of  a  purple 
colour ;  and  a  solution  of  oxy-haernoglobin  may  be  made  to  give  up 
oxygen  and  to  become  purple  in  a  similar  manner. 

This  change  may  be  also  effected  by  passing  through  it  hj-drogen 
or  nitrogen  gas,  or  by  the  action  of  reducing  agents,  of  which 
Stokes's  fluid*  is  the  most  convenient. 

With  the  spectroscope,  a  solution  of  deoxidized  haemoglobin  is 
found  to  give  an  entirely  different  appearance  from  that  of  oxidized 
haemoglobin.  Instead  of  the  two  bands  at  d  and  e  we  find  a 
single  broader  but  fainter  band  occupying  a  position  midway 
between  the  two,  and  at  the  same  time  less  of  the  blue  end  of  the 
spectrum  is  absorbed.  Even  in  strong  solutions  this  latter  ap- 
pearance is  found,  thereby  differing  from  the  strong  solution  of 
oxidised  haemoglobin  which  lets  through  only  the  red  and  orange 
rays ;  accordingly  to  the  naked  eye  the  one  (reduced  haemoglobin 
solution)  appears  purple,  the  other  (oxy- haemoglobin  solution)  red. 
The  deoxidised  crystals  or  their  solutions  quickly  absorb  oxygen 
on  exposure  to  the  air,  becoming  scarlet.  If  solutions  of  blood  be 
taken  instead  of  solutions  of  haemoglobin,  results  similar  to  the 
whole  of  the  foregoing  can  be  obtained. 


*  Stokes's  Fluid  consists  of  a  solution  of  ferrous  sulphate,  to  which 
ammonia  has  been  added  and  sufficient  tartaric  acid  to  prevent  precipita- 
tion. Another  reducing  agent  is  a  solution  of  stannous  chloride,  treated  in 
a  way  similar  to  the  ferrous  sulphate,  and  a  third  re-agent  of  like  nature  is 
an  aqueous  solution  of  ammonium  sulphide. 


ABSORPTION    SP 


1  Spectrum  of  Aiv  rraunhofer's 

2.  Blood;  i.  e  a  suronq  solution  of  Oxyhemoglobin  &  reduced  Haemogl:. 


3.  Blood  more  ii. 

4Redu   ed    -  -  uogioLin 

G 

&  Sulphuretted  Hydrogen  jam 


and  cole  it  in  Chlor 


5  le  compc 

7 

.    [ 


fpectra  draunfrom  obscrixrtians  6i   .V H .  Z<yorrzrA-  /C  S 

■ .-.  &  Ca  London 


chat.  iv.  J  EJEMOGLOBIN.  u- 

Venous  blood  nev<  .  pt  in  the  last  stages  f  asphyxia,  fails 
to  show  the  oxy-haemoglobin  bands,  inasmuch  as  the  greater  part 
of  the  haemoglobin  even  in  venous  blood  exists  in  the  more  highly 
oxidized  condition. 

Action  of  Gases  on  Haemoglobin. — Carbonic  oxide,  paf 
through  a  solution  of  haemoglobin,  causes  it  to  assume  a  bluish 
colour,  and  the  spectrum  is  slightly  altered  \  two  bands  are  still 
visible,  but  are  somewhat  nearer  the  blue  end  than  those  of 
oxy-haemoglobin  (see  plate).  The  amount  of  carbonic  oxide  is 
equal  to  the  amount  of  the  oxygen  displaced.  Although  the  car 
bonic  oxide  gas  readily  displaces  oxygen,  the  reverse  is  not  the 

-  .  and  upon  this  property  depends  the  dangerous  effect  of  coal 
»isoning.  Coal  gas  contains  much  carbonic  oxide,  and  this 
at  once,  when  breathed,  combines  with  the  haemoglobin  of  the 
blood,  producing  a  compound  which  cannot  easily  be  reduced,  and 
since  it  is  by  no  means  an  oxygen  carrier,  death  may  result  from 
suffocation  from  want  of  oxygen  notwithstanding  the  free  entry 
into  the  lungs  of  pure  air.  Crystals  of  carbonic-oxide  haemoglobin 
ly  resemble  those  of  oxyhemoglobin. 

Nitric  oxide  produces  a  similar  compound  to  the  carbonic-oxide 
haemoglobin,  which  is  even  less  easily  reduced. 

Nitrous  oxide  reduces  oxyhaemoglobin,  and  therefore  leaves  the 
reduced  haemoglobin  in  a  condition  to  actively  take  up  oxygen. 

S  'phuretted  Hydrogen. — If  this  gas  be  passed  through  a  solu- 
tion of  oxyhemoglobin,  the  haemoglobin  is  reduced  and  an  additional 
band  appears  in  the  red.  If  the  solution  be  then  shaken  with  air, 
the  two  Viands  of  oxyhaemoglobin  replace  that  of  reduced  haemo- 
globin, but  the  band  in  the  red  per-ists. 

Products  of  the  Decomposition  of  Haemoglobin. 

Methaemoglobin. — If  an  aqueous  solution  of  oxyhaemoglobin 
be  exposed  to  the  air  for  some  time,  its  spectrum  undergoes  a 
change  ;  the  two  p  and  e  bands  become  faint,  and  a  new  line  in 
the  red  at  c  is  developed.  The  solution,  too,  has  become  brown 
and  acid  in  reaction,  and  is  precipitable  by  basic  lead  acetate. 
This  change  is  due  to  the  decomposition  of  haemoglobin,  and  to  the 
production  of  methoBmoglobin.  On  adding  ammonium  sulphide, 
reduced  haemoglobin  is  produced,  and  on  shaking  this  up  with 
air,  oxyhaemoglobin  is  reproduced. 

I  2 


1 1 6  THE    BLOOD.  [chap.  iv. 

Hsematin. — By  the  action  of  heat,  or  of  acids  or  alkalies  in  the 
presence  of  oxygen,  haemoglobin  can  be  split  up  into  a  substance 
called  Hcematin,  which  contains  all  the  iron  of  the  haemoglobin 
from  which  it  was  derived,  and  a  proteid  residue.  Of  the  latter 
it  is  impossible  to  say  more  than  that  it  is  probably  made  up  of 
one  or  more  bodies  of  the  globulin  class.  If  there  be  no  oxygen 
present,  instead  of  hsematin  a  body  called  hoemochromogen  is 
produced,  which,  however,  will  speedily  undergo  oxidation  into 
hsematin. 

Hsematin  is  a  dark  brownish  or  black  non-crystallizable  sub- 
stance of  metallic  lustre.  Its  percentage  composition  is  C. 
64*30;  H.  S'5°)  N«  9'°6  ;  Fe,  8*82;  0.  12-32;  which  gives  the 
formula  C^  EL0,  X3,  Fe,,  0I0  (Hoppe-Seyler).  It  is  insoluble  in 
water,  alcohol,  and  ether ;  soluble  in  the  caustic  alkalies  ;  soluble 
with  difficulty  in  hot  alcohol  to  which  is  added  sulphuric  acid. 
The  iron  may  be  removed  from  hsematin  by  heating  it  with 
fuming  hydrochloric  acid  to  3200  F.  (160°  C),  and  a  new  body, 
hcematoyjorphyrin,  is  produced. 

In  acid  solution. — If  to  blood  an  excess  of  acetic  acid  be  added, 
the  colour  alters  to  brown  from  decomposition  of  haemoglobin,  and 
the  setting  free  of  haematin  ;  by  shaking  this  solution  with  ether 
solution  of  the  haematin  is  obtained.  The  spectrum  of  the 
etherial  solution  shows  no  less  than  four  absorption  bands,  viz., 
one  in  the  red  between  c  and  d,  one  faint  and  narrow  close  to 
D,  and  then  two  broader  bands,  one  between  d  and  e,  and  another 
nearly  midway  between  b  and  f.  The  first  band  is  by  for  the 
most  distinct,  and  the  acid  solution  of  haematin  without  ether 
shows  it  plainly. 

In  alkaline  solution. — The  absorption  band  is  still  in  the  red, 
but  nearer  to  d,  and  the  blue  end  of  the  spectrum  is  partially 
absorbed  to  a  considerable  extent.  If  a  reducing  agent  be 
added,  two  bands  resembling  those  of  oxyhaenioglobin,  but 
nearer  to  the  blue,  appear  ;  this  is  the  spectrum  of  reduced 
hcematin.  On  shaking  the  reduced  haematin  with  air  or  oxygen 
the  two  bands  are  replaced  by  the  single  band  of  alkaline 
haematin. 

Hsematoidin. — This  substance  is  found  in  the  form  of  yellowish 
crystals  in  old  blood  extravasations,  and  is  derived  from  the 
haemoglobin.     Their  crystalline  .form  and  the  reaction  they  give 


CHAP.  IT.]  ILi:.ML\.  117 

with  nitric  acid  seem  to  show  them  to  be  identical  with  Bilirubin, 
the  chief  colouring  matter  of  the  Bile. 


Fig.  84. — ]!<•  Hiatoidin  crystals.     (Frey.) 

Hsemin. —  One  of  the  most  important  derivatives  of  hsematin 
is  Hsemin.  It  is  usually  called  Hydrochlorate  of  Hcematin  (or 
hydrochloride),  but  its  exact  chemical  composition  is  uncertain. 
Its  formula  is  Qm  H70,  N8,  Fe2,  0IO,  2  Hcl,  and  it  contains  5*18  per 
cent,  of  chlorine,  but  by  some  it  is  looked  upon  as  simply  crys- 
tallized hsematin.  Although  difficult  to  obtain  in  bulk,  a  speci- 
men may  be  easily  made  for  the  microscope  in  the  following 
way  : — A  small  drop  of  dried  blood  is  finely  powdered  with  a  few 
crystals  of  common  salt  on  a  glass  slide,  and  spread  out;  a  cover  glass 


Fig.  85.— Hcemin  crystals.    (Frey.) 


is  then  placed  upon  it,  and  glacial  acetic  acid  added  by  means  of  a 
capillary  pipette.  The  blood  at  once  turns  of  a  brownish  colour. 
The  slide  is  then  heated,  and  the  acid  mixture  evaporated  to 
dryness  at  a  high  temperature.  The  excess  of  salt  is  washed  away 
with  water  from  the  dried  residue,  and  the  specimen  may  then  be 
mounted.  A  large  number  of  small,  dark,  reddish  black  crystals 
of  a  rhombic  shape,  sometimes  arranged  in  bundles,  will  be  seen 
if  the  slide  be  subjected  to  microscopic  examination. 

The  formation  of  these  hamiin  crystals  is  of  great  interest  and 


Il8  THE    BLOOD.  [chav.  iv. 

importance  from  a  medico-legal  point  of  view,  as  it  constitutes  the 
most  certain  and  delicate  test  we  have  for  the  presence  of  blood 
(not  of  necessity  the  blood  of  man)  in  a  stain  on  clothes,  &c.  It 
exceeds  in  delicacy  even  the  spectroscopic  test. 

Estimation  of  Haemoglobin. — The  most  exact  method  is  by 
the  estimation  of  the  amount  of  iron  in  a  given  specimen  of  blood, 
but  as  this  is  a  somewhat  complicated  process,  a  method  has  been 
proposed  which,  though  not  so  exact,  has  the  advantage  of 
simplicity.  This  consists  in  comparing  the  colour  of  a  given 
small  amount  of  diluted  blood  with  glycerine  jelly  tinted  with  car- 
mine and  picrocarmine  to  represent  a  standard  solution  of  blood 
diluted  one  hundred  times.  The  amount  of  dilution  which  the 
given  blood  requires  will  thus  approximately  represent  the  quan- 
tity of  haemoglobin  it  contains.     (Gowers.) 

Distribution  of  Hsemoglobin. — In  connection  with  the  ascer- 
tained function  of  haemoglobin  as  the  great  oxygen-carrier,  the 
following  facts  with  regard  to  its  distribution  are  of  importance. 

It  occurs  not  only  in  the  red  blood-cells  of  all  Vertebrata  (except 
one  fish  (leptocephalus)  whose  blood-cells  are  all  colourless),  but 
also  in  similar  cells  in  many  "Worms  :  moreover,  it  is  found  diffused 
in  the  vascular  fluid  of  some  other  worms  and  certain  Crustacea  ; 
it  also  occurs  in  all  the  striated  muscles  of  Mammals  and  Birds. 
It  is  generally  absent  from  unstriated  muscle  except  that  of  the 
rectum.  It  has  also  been  found  in  Mollusca  in  certain  muscles 
which  are  specially  active,  viz.,  those  which  work  the  rasp-like 
tongue. 

In  the  muscles  of  Fish  it  has  hitherto  only  been  met  with  in  the 
very  active  muscle  which  moves  the  dorsal  fin  of  the  Hippocampus 
(Ray  Lankester). 

The  Carbon  Dioxide  Gas  in  the  Blood. — Of  this  gas  in 
the  blood,  part  exists  in  a  state  of  simple  solution  in  the  serum, 
and  the  rest  in  a  state  of  weak  chemical  combination.  It  is 
believed  that  the  latter  is  combined  with  the  sodium  carbonate  in 
a  condition  of  bicarbonate.  Some  observers  consider  that  part  of 
the  gas  is  associated  with  the  corpuscles. 

The  Nitrogen  in  the  Blood. — It  is  believed  that  the  whole 
of  the  small  quantity  of  the  nitrogen  contained  in  the  blood  is 
-imply  dissolved  in  the  fluid  plasma. 


csaf.it.]  DEVELOPMENT    OF    THE    BLOOD.  ug 


Development  of  the  Blood. 

The  first  formed  blood-corpuscles  of  the  human  embryo  differ 
much  in  their  general  characters  from  those  which  belong  to  the 
later  periods  of  intra-uterine,  and  t<>  all  periods  of  extra-uterine 

life.      Their  manner  of  origin  is  at  first  very  simple. 

Surrounding  the  early  embryo  is  a  circular  area,  called  the 
vascular  area,  in  which  the  first  rudiments  of  the  blood-vessels  and 
blood-corpuscles  are  developed.      Here  the  nucleated  embryonal 


4 


■■©■■■ 


Fig.  86. — Jtorf  o/tfc  network  of  developing  blood-vessels  in  the  vascular  area  of  a  guinea-pig. 
hi,  blood-corpuscles  becoming  free  in  an  enlarged  and  hollowed  out  part  of  the  net- 
work ;  o,  process  of  protoplasm.     (E.  A.  Schiifer.) 

cells  of  the  mesoblast,  from  which  the  blood-vessels  and  cor- 
puscles are  to  be  formed,  send  out  processes  in  various  directions, 
and  these  joining  together,  form  an  irregular  meshwork.  The 
nuclei  increase  in  number,  and  collect  chiefly  in  the  larger 
masses  of  protoplasm,  but  partly  also  in  the  processes.  These 
nuclei  gather  around  them  a  certain  amount  of  the  protoplasm, 
and  becoming  coloured,  form  the  red  blood  corpuscles.  The 
protoplasm  of  the  cells  and  their  branched  network  in  which  these 
corpuscles  lie  then  becomes  hollowed  out  into  a  system  of  canals 
enclosing  fluid,  in  which  the  red  nucleated  corpuscles  float.  The 
corpuscles  at  first  are  from  about  aBx6tf  to  xriny  °^  an  mcn  m 
diameter,  mostly  spherical,  and  with  granular  contents,  and  a 
well-marked  nucleus.     Their  nuclei,  which  are  about  -^Vo  of  an 


120 


THE    BLOOD. 


[CHAP.  IV. 


inch  in  diameter,  are  central,  circular,  very  little  prominent  on 
the  surfaces  of  the  corpuscle,  and  apparently  slightly  granular  or 
tuberculated. 

The  corpuscles  then  strongly  resemble  the  colourless  corpuscles 
of  the  fully  developed  blood,  but  are  coloured.  They  are  capable 
of  amoeboid  movement  and  multiply  by  division. 

When,  in  the  progress  of  embryonic  development,  the  liver 
begins  to  be  formed,  the  multiplication  of  blood-cells  in  the  whole 
mass  of  blood  ceases,  and  new  blood-cells  are  produced  by  this 
organ,  and  also  by  the  lymphatic  glands,  thymus  and  spleen. 
These  are  at  first  colourless  and  nucleated,  but  afterwards  acquire 
the  ordinary  blood-tinge,  and  resemble  very  much  those  of  the 
first  set.  They  also  multiply  by  division.  In  whichever  way 
produced,  however,  whether  from  the  original  formative  cells  of 
the  embryo,  or  by  the  liver  and  the  other  organs  mentioned  above, 
these  coloured  nucleated  cells  begin  very  early  in  foetal  life  to  be 
mingled  with  coloured  non-nucleated  corpuscles  resembling  those 
of  the  adult,  and  at  about  the  fourth  or  fifth  month  of  embryonic 
existence  are  completely  replaced  by  them. 

Origin  of  the  Mature  Red  Corpuscles. — The  non-nucleated 
red  corpuscles  may  possibly  be  derived  from  the  nucleated,  but  in 
all  probability  are  an  entirely  new  formation,  and  the  methods  of 


I  .-■    •- . — Bevelcj  From  the  subcutaneous 

:>sue  of  a  new-born  rat.     h,  a  cell  containing  hfenioglobin  in  a  diffused  form  in  the 

protoplasm  :  /<',  one  containing  coloured  globules  of  varying  size  and  vacuoles  ;  h" .  a 

cell  filled  ■with  coloured  eiobules  of  nearlv  uniform  size :  f.  r",  developing  fat  cells. 

E.  A.  Schafer.) 


their  origin  are  the  following: — (i.)  During  fcetal  life  and  possibly 
in  some  animals,  e.g.,  the  rat,  which  are  born  in  an  immature 
condition,  for  some  little  time  after  birth,  the  blood  discs  arise  in 
the  connective  tissue  cells  in  the  following  way.     Small  globules, 


'  BAP.  iv.  | 


DEVELOPMENT  OF  THE  BLOOD. 


121 


of  varying  Bize,  ofoolouring  matter  arise  in  the  protoplasm  "f  tho 
cells,  and  the  cells  themselves  become  branched,  their  branches 
joining  the  branches  of  similar  cells.  The  culls  next  become 
vacuolated,  and  the  red  globules  are  free  in  a  cavity  filled  with 
fluid  (fig.  S8)  ;  by  the  extension  of  the  cavity  of  the  cells  into 
their  processes  anastomosing  vessels  are  produced,  which  ultimately 
join  with  the  previously  existing  vessels,  and  the  globules,  now 
having  the  size  and  appearance  of  the  ordinary  red  corpuscles,  are 


^ 


J. — Further  development  of  blood-corpuscles  in  <:oi,  -  "nd  transformation  of 

the  latter  into  capillary  bli      -  -.     a,  an  elongated  cell  with  a  cavity  in  the  proto- 

plasm occupied  by  fluid  and  by  blood-corpuscles  which  are  still  globuiar;  b,  a  hollow 
cell,  the  nucleus  of  which  has  multiplied.  The  new  nuclei  are  arranged  around  the 
wall  of  the  cavity,  the  corpuscles  in  which  have  now  become  discord  ;  c,  shows  the  mode 
of  union  of  a  "  htemapoietic  "  cell,  which,  in  this  instance,  contains  only  one  corpuscle, 
with  the  prolongation  [hi]  of  a  previously  existing  vessel ;  a  and  c,  from  the  new-born 
rat ;  b,  from  the  foetal  sheep.      E.  A.  Scnafer.) 


passed  into  the  general  circulation.     This  method  of  formation  is 
called  intracellular  (Schafer). 

(2.)  From  the  white  corpuscles. — The  belief  that  the  red  cor- 
puscles are  derived  from  the  white  is  still  very  general,  although 
no  new  evidence  has  been  recently  advanced  in  favour  of  this 
view.  It  is,  however,  uncertain  whether  the  nucleus  of  the  white 
corpuscle  becomes  the  red  corpuscle,  or  whether  the  whole  white 
corpuscle  is  bodily  converted  into  the  red  by  the  gradual  clearing 
up  of  its  contents  with  a  disappearance  of  the  nucleus.  Probably 
the  latter  view  is  the  correct  one. 


122  THE    BLOOD.  [chap.  iv. 

(3.)  From  the  medulla  of  bones. — Red  corpuscles  are  to  a  very  large 
extent  derived  during  adult  life  from  the  large  pale  cells  in  the 
red  marrow  of  bones,  especially  of  the  ribs  (figs.  44,  89).  These 
cells  become  coloured  from  the  formation  of  haemoglobin  chiefly  in 
one  part  of  their  protoplasm.     This  coloured  part  becomes  sepa- 


Fig.  89. — Coloured  nucleated  corpuscles,  from  the  red  marrow  of  the  guinea-pig. 

(E.  A.  ScMfer.) 

rated  from  the  rest  of  the  cell  and  forms  a  red  corpuscle,  being 
at  first  cup-shaped,  but  soon  taking  on  the  normal  appearance 
of  the  mature  corpuscle.  It  is  supposed  that  the  protoplasm 
may  grow  up  again  and  form  a  number  of  red  corpuscles  in  a 
similar  way. 

(4.)  From  the  tissue  of  the  spleen. — It  is  probable  that  red  as 
well  as  white  corpuscles  may  be  produced  in  the  spleen. 

(5.)  From  Microcytes. — Hayem  describes  the  small  particles 
(microcytes),  previously  mentioned  as  contained  in  the  blood 
(p.  94),  and  which  he  calls  hsematoblasts,  as  the  precursors  of  the 
red  corpuscles.  They  acquire  colour,  and  enlarge  to  the  normal 
size  of  red  corpuscles. 

Without  doubt,  the  red  corpuscles  have,  like  all  other  parts 
of  the  organism,  a  tolerably  definite  term  of  existence,  and  in  a 
like  manner  die  and  waste  away  when  the  portion  of  work  allotted 
to  them  has  been  performed.  Neither  the  length  of  their  life, 
however,  nor  the  fashion  of  their  decay  has  been  yet  clearly  made 
out.  It  is  generally  believed  that  a  certain  number  of  the  red 
corpuscles  undergo  disintegration  in  the  spleen ;  and  indeed 
corpuscles  in  various  degrees  of  degeneration  have  been  observed 
in  this  organ. 

Origin  of  the  Colourless  Corpuscles.  —  The  colourless 
corpuscles  of  the  blood  are  derived  from  the  lymph  corpuscles, 
being,  indeed,  indistinguishable  from  them  ;  and  these  come  chiefly 
from  the  lymphatic  glands.  Their  number  is  increased  by 
division. 

Colourless  corpuscles  are  also  in  all  probability  derived  from 
the   spleen  and  thymus,  and  also  from  the  germinating  endothe- 


chap,  iv.]  r>i:>    OF    THE    BLOOD,  j 23 

limn  of  serous  membranes,  and  from  connective  tissue.  The 
corpuscles  are  carried  into  the  blood  either  with  the  lymph  and 
ohyle,  or  pass  directly  from  the  Lymphatic  tissue  in  which  they 
have  been  formed  into  the  neighbouring  blood-vessels. 


Uses  of  the  Blood. 

1.  To  be  a  medium  for  the  reception  and  storing  of  matter 
(ordinary  food,  drink,  and  oxygen)  from  the  outer  world,  and  for 
its  conveyance  to  all  parts  of  the  body. 

2.  To  be  a  source  whence  the  various  tissues  of  the  body  may 
take  the  materials  necessary  for  their  nutrition  and  maintenance  ; 
and  whence  the  secreting  organs  may  take  the  constituents  of 
their  various  secretions. 

3.  To  be  a  medium  for  the  absorption  of  refuse  matters  from  all 
the  tissues,  and  for  their  conveyance  to  those  organs  whose  function 
it  is  to  separate  them  and  cast  them  out  of  the  body. 

4.  To  warm  and  moisten  all  parts  of  the  body. 

Uses  of  the  various  Constituents  of  the  Blood. 

Albumen. — Albumen,  which  exists  in  so  large  a  proportion 
among  the  chief  constituents  of  the  "blood,  is  without  doubt  mainly 
for  the  nourishment  of  those  textures  which  contain  it  or  other 
compounds  nearly  allied  to  it. 

Fibrin. — In  considering  the  functions  of  fibrin,  we  may  exclude 
the  notion  of  its  existence,  as  such,  in  the  blood  in  a  fluid  state, 
and  of  its  use  in  the  nutrition  of  certain  special  textures,  and  look 
for  the  explanation  of  its  functions  to  those  circumstances,  whether 
of  health  or  disease,  under  which  it  is  produced.  In  haemorrhage, 
for  example,  the  formation  of  fibrin  in  the  clotting  of  blood,  is  the 
means  by  which,  at  least  for  a  time,  the  bleeding  is  restrained  or 
stopped  ;  and  the  material  or  blastema  which  is  produced  for  the 
permanent  healing  of  the  injured  part,  contains  a  coaguahle 
material  identical,  or  very  nearly  so,  with  the  fibrin  of  clotted 
blood. 

Fatty  Matters.— The  fatty  matters  of  the  blood  subserve  more 
than  one  purpose.  For  while  they  are  the  means,  in  part,  by 
which   the   fat  of  the  body,  so  widely  distributed   in  the  proper 


124  CIRCULATION    OF    THE    BLOOD.  [chap.  v. 

adipose  and  other  textures,  is  replenished,  they  also,  by  their 
union  with  oxygen,  assist  in  maintaining  the  temperature  of  the 
body.  To  certain  secretions  also,  notably  the  milk  and  bile, 
fat  is  contributed. 

Saline  Matter. — The  uses  of  the  saline  constituents  of  the  blood 
are,  first,  to  enter  into  the  composition  of  such  textures  and 
secretions  as  naturally  contain  them,  and,  secondly,  to  assist  in 
preserving  the  due  specific  gravity  and  alkalinity  of  the  blood,  and 
in  preventing  its  decomposition.  The  phosphate  and  carbonate  of 
sodium,  to  which  the  blood  owes  its  alkaline  reaction,  increase  the 
absorptive  power  of  the  serum  for  gases. 

Corjyuscles. — The  important  use  of  the  red  corpuscles  is  in 
relation  to  the  absorption  of  oxygen  in  the  lungs,  and  its  convey- 
ance to  the  tissues.  How  far  the  red  corpuscles  are  actually 
concerned  in  the  nutrition  of  the  tissues  is  quite  unknown. 

The  relation  of  the  colourless  corpuscles  to  the  coagulation  of 
the  blood  has  been  already  considered;  of  their  functions,  other 
than  are  concerned  in  this  phenomenon,  and  in  the  regeneration 
of  the  red  corpuscles,  nothing  is  positively  known. 


CHAPTEE    Y. 

THE    CIRCULATION    OF    THE    BLOOD. 

The  Heart  is  a  hollow  muscular  organ  containing  four  cham- 
bers, two  auricles  and  two  ventricles,  arranged  in  pairs.  On 
each  side  (right  and  left)  of  the  heart  is  an  auricle  joined  to  and 
communicating  with  a  ventricle,  but  the  chambers  on  the  right 
side  do  not  directly  communicate  with  those  on  the  left  side. 
The  circulation  of  the  blood  is  chiefly  carried  on  by  the  contrac- 
tion of  the  muscular  walls  of  these  chambers  of  the  heart,  the 
auricles  contracting  simultaneously,  and  their  contraction  being- 
followed  by  the  simultaneous  contraction  of  the  ventricles.  The 
blood  is  conveyed  away  from  the  left  side  of  the  heart  by  the 
arteries,  and  returned  to  the  right  side  of  the  heart  by  the  veins, 
the  arteries  and  veins  being  continuous  with  each  other  at  one  end 


en. v.: 


THE    HEART. 


125 


by  means  of  the  heart,  and  at  the  other  by  a  fine  network  of  v- 
called  t!.  The  blood,  th<  s     from 

the  heart  paaaea  first  into  the  arteries,  then  into  the  capill 
and  lastly  into  the  veins,  by  which  it  is  conveyed  back  again  to 

the  heart,  thus  completing  a  n  1  lotion. 


F:_ .  go. — Diagram  of  the  Circulation. 


The  right  side  of  the  heart  d'.»es  not  directly  coinruunicate  with 
the  left  to  complete  the  entire  circulation,  but  the  blood  has  to  pass 
from  the  right  side  to  the  lungs,  through  the  pulmonary  art 
then  through  the  pulmonary  capUlary-vese  Is  aid  through  the 
pulmonary  veins  to  the  left  side  of  the  heart.  Thus  there  are 
two  circulations  by  which  the  bloc-  ffl  ;  the  one,  a  shorter 

circuit  from  the  right  aide  ft  heart  t<>  the  lungs  and  back 
again  to  the  left  side  of  the  heart  :  the  other  and  larger  circuit. 
from  the  le  of  the  heart  to  all  parts  of  the  body  and  back 


126 


CIRCULATION  OF  THE  BLOOD. 


[•HAP.   V. 


again  to  the  right  side :  but  more  strictly  speaking,  there  is 
only  one  complete  circulation,  which  may  be  diagrammaticallv 
represented  by  a  double  loop,  as  in  the  accompanying  figure 
(fig.  90). 

On  reference  to  this  figure,  and  noticing  the  direction  of  the 
arrows,  which  represent  the  course  of  the  stream  of  blood,  it  will 
be  observed  that  while  there  is  a  smaller  and  a  larger  circle,  both  of 
which  pass  through  the  heart,  yet  that  these  are  not  distinct,  one  from 


Pulmonary 

Artery. 


Diaphragm 

F  -      :  —  I  lungs  in  situ.     The  front  portion  of  the  chest-wall,  and  the 

onter  or  yexs  of  the  pleurce  and  pericardium  have  been  removed.    The  lungs 

are  partly  collapsed. 


the  other,  but  are  formed  really  by  one  continuous  stream,  the  whole 
of  which  must,  at  one  part  of  its  course,  pass  through  the  lungs. 
Subordinate  to  the  two  principal  circulations,  the  Pulmonary  and 
Systemic,  as  they  are  named,  it  will  be  noticed  also  in  the  same  figure 
that  there  is  another,  by  which  a  portion  of  the  stream  of  blood 
having  been  diverted  once  into  the  capillaries  of  the  intestinal 
canal,  and  some  other  organs,  and  gathered  up  again  into  a  single 
stream,  is  a  second  time  divided  in  its  passage  through  the 
liver,  before  it  finally  reaches  the  heart  and  completes  a  revolu- 
tion. This  subordinate  stream  through  the  liver  is  called  the 
Portal  circulation. 


chap.  v.J  THE    PERICABDIUM.  l2j 

The  Forces  concerned  in  the  Circulation  of  the  Blood.— 
(i)  The  principal  force  provided  for  constantly  moving  the  blood 
through  the  course  of  the  circulation  is  that  of  the  muscular  sub- 
stance of  the  heart  ;  Other  assistant  forces  are  (2)  those  of  the 
elastic  walls  of  the  arteries,  (3)  the  pressure  of  the  muscles  among 
which  some  of  the  veins  run,  (4)  the  movements  of  the  walls  of 
the  chest  in  respiration,  and  probably,  to  some  extent,  (5)  the 
interchange  of  relations  between  the  blood  and  the  tissues  which 
occurs  in  the  capillary  system  during  the  nutritive  processes. 

The  Heart. 

The  Pericardium. — The  heart  is  invested  by  a  membranous 
sac — the  pericardium,  which  is  made  up  of  two  distinct  parts,  an 
rnal  fibrous  membrane,  composed  of  closely  interlacing  fibres, 
which  has  its  base  attached  to  the  diaphragm — both  to  the 
central  tendon  and  to  the  adjoining  muscular  fibres,  while  the 
smaller  and  upper  end  is  lost  on  the  large  blood-vessels  by 
mingling  its  fibres  with  that  of  their  external  coats ;  and  an 
internal  serous  layer,  which  not  only  lines  the  fibrous  sac,  but 
also  is  reflected  on  to  the  heart,  which  it  completely  invests. 
The  part  which  lines  the  fibrous  membrane  is  called  the  parietal 
layer,  and  that  enclosing  the  heart,  the  visceral  layer,  and  these 
being  continuous  for  a  short  distance  along  the  great  vessels 
of  the  base  of  the  heart,  form  a  closed  sac,  the  cavity  of  which 
in  health  contains  just  enough  fluid  to  lubricate  the  two  surfaces, 
and  thus  enable  them  to  glide  smoothly  over  each  other  during 
the  movements  of  the  heart.  Most  of  the  vessels  passing  in  and 
<»ut  of  the  heart  receive  more  or  less  investment  from  this  sac. 

The  heart  is  situated  in  the  chest  behind  the  sternum  and 
costal  cartilages,  being  placed  obliquely  from  right  to  left,  quite 
two-thirds  to  the  left  of  the  mid-sternal  line.  It  is  of  pyramidal 
shape,  with  the  apex  pointing  downwards,  outwards,  and  towards 
the  left,  and  the  base  backwards,  inwards,  ami  towards  the  right. 
It  rests  upon  the  diaphragm,  and  its  pointed  apex,  formed  exclu- 
sively of  the  left  side  of  the  heart,  is  in  contact  with  the  chest 
wall,  and  during  life  beats  against  it  at  a  point  called  the  apex  beat, 
situated  in  the  fifth  intercostal  space,  about  two  inches  below  the 
left  nipple,  and  an  inch  and  a  half  to  the  sternal  side.  The  heart 
is  suspended  in  the  chest  by  the  large  vessels  which  proceed  from 


128  CIRCULATION    OF    THE    BLOOD.  [chap.  v. 

its  base,  but,  excepting  the  base,  the  organ  itself  lies  free  in  the 
sac  of  the  pericardium.  The  part  which  rests  upon  the  diaphragm 
is  flattened,  and  is  known  as  the  posterior  surface,  whilst  the  free 
upper  part  is  called  the  anterior  surface.  The  margin  towards 
the  left  is  thick  and  obtuse,  whilst  the  lower  margin  towards  the 
right  is  thin  and  acute. 

On  examination  of  the  external  surface  the  division  of  the  heart 
into  parts  which  correspond  to  the  chambers  inside  of  it  may  be 
traced,  for  a  deep  transverse  groove  called  the  auriculo-ventricular 
groove  divides  the  auricles  which  form  the  base  of  the  heart  from 
the  ventricles  which  form  the  remainder,  including  the  apex,  the 
ventricular  portion  being  by  far  the  greater ;  and,  again,  the 
inter-ventricular  groove  runs  between  the  ventricles  both  front 
and  back,  and  separates  the  one  from  the  other.  The  anterior 
groove  is  nearer  the  left  margin  and  the  posterior  nearer  the 
right,  as  the  front  surface  of  the  heart  is  made  up  chiefly  of  the 
right  ventricle  and  the  posterior  surface  of  the  left  ventricle.  In 
the  furrows  run  the  coronary  vessels,  which  supply  the  tissue  of 
the  heart  itself  with  blood,  as  well  as  nerves  and  lymphatics 
imbedded  in  more  or  less  fatty  tissue. 

The  Chambers  of  the  Heart. — The  interior  of  the  heart  is 
divided  by  a  partition  in  such  a  manner  as  to  form  two  chief 
chambers  or  cavities — right  and  left.  Each  of  these  chambers  is 
again  subdivided  into  an  upper  and  a  lower  portion,  called  respec- 
tively, as  already  incidentally  mentioned,  auricle  and  ventricle, 
which  freely  communicate  one  with  the  other  ;  the  aperture  of 
communication,  however,  being  guarded  by  valves,  so  disposed  as 
to  allow  blood  to  pass  freely  from  the  auricle  into  the  ventricle, 
but  not  in  the  opposite  direction.  There  are  thus  four  cavities 
altogether  in  the  heart — two  auricles  and  two  ventricles;  the 
auricle  and  ventricle  of  one  side  being  quite  separate  from  those 
of  the  other  (fig.  90). 

Right  Auricle. — The  right  auricle  is  situated  at  the  right  part 
of  the  base  of  the  heart  us  viewed  from  the  front.  It  is  a  thin  walled 
cavity  of  more  or  less  quadrilateral  shape,  prolonged  at  one  corner 
into  a  tongue-shaped  portion,  the  right  auricular  appendix,  which 
slightly  overlaps  the  exit  of  the  great  artery,  the  aorta,  from  the  heart. 

The  interior  is  smooth,  being  lined  with  the  general  lining  of 
the  heart,  the   endocardium,  and  into   it  open    the  superior  and 


CHA1 


(  HAMBERS    OF    THE    EEART. 


Inferior  venae  cavae,  or  greal  veins,  which  convey  the  blood  from 
all  parta  of  the  body  to  the  heart  Tin'  former  is  directed  down- 
wards and  forwards,   the   latter  upwards  and   inwards;    between 


Fig.  92.— The  right  auricle  ■',  and  a  part  of  their  right  and  anterior 

Us  removed,  -how  their  interior,    |.— i,  superior  vena  cava;  2,  inferior  vena 

it  Bhort :  3,  light  auricle ;  3',  placed  in  the  fossa  ovalis,  below 
which  is  the  Eustachian  valve  ;  j ',  is  placed  close  to  the  aperture  of  the  coronary  vein ; 
— .  — .  placed  in  the  auriculo- ventricular  groove,  where  a  narrow  portion  of  the  adja- 
cent walls  of  the  auricle  and  ventricle  has  been  preserved;  4,  4,  cavity  of  the  right 
ventricle,  the  upper  figure  is  immediately  below  the  semilunar  valves ;  4',  large  columna 
carnea  or  musculus  papillaris ;  5,  5',  5",  tricuspid  valve  ;  6,  placed  in  the  interior  of 
the  pulmonary  artery,  a  part  of  the  anterior  wall  of  that  vessel  having  been  removed, 
and  a  narrow  "portion  of  it  preserved  at  its  commencement,  where  the  semilunar  valves 
are  attached ;  7,  concavity  of  the  aortic  arch  close  to  the  cord  of  the  ductus  arteriosus ; 
8,  ascending  part  or  sinus  of  the  arch  covered  at  its  commencement  by  the  auricular 
appendix  and  pulmonarv  artery ;  9,  placed  between  the  innominate  and  left  carotid 
arteries  ;  10,  appendix  of' the  left  auricle  ;  11,  11,  the  outside  of  the  left  ventricle,  the 
lower  figure  near  the  apex  (Allen  Thomson). 

the  entrances  of  these  vessels  is  a  Blight  tubercle  called  tubercle 
of  Lower.  The  opening  of  the  inferior  cava  is  protected  and 
partly  covered  by  a  membrane  called  the  Eustachian  valve.     In 


130  CIRCULATION    OF    THE    BLOOD.  [chap,  v, 

the  posterior  wall  of  the  auricle  is  a  slight  depression  called  the 
fossa  ovalis,  which  corresponds  to  an  opening  between  the  right 
and  left  auricles  which  exists  in  fcetal  life.  The  right  auricular 
appendix  is  of  oval  form,  and  admits  three  fingers.  Various  veins, 
including  the  coronary  sinus,  or  the  dilated  portion  of  the  right 
coronary  vein,  open  into  this  chamber.  In  the  appendix  are 
closely  set  elevations  of  the  muscular  tissue  covered  with  endo- 
cardium, and  on  the  anterior  wall  of  the  auricle  are  similar 
elevations  arranged  parallel  to  one  another,  called  musculi 
pectinati. 

Right  Ventricle. — The  right  ventricle  occupies  the  chief  part 
of  the  anterior  surface  of  the  heart,  as  well  as  a  small  part  of  the 
posterior  surface  :  it  forms  the  right  margin  of  the  heart.  It 
takes  no  part  in  the  formation  of  the  apex.  On  section  its  cavity, 
in  consequence  of  the  encroachment  upon  it  of  the  septum 
ventriculorum,  is  semilunar  or  crescentic  (fig.  94)  ;  into  it  are  two 
openings,  the  auriculo-ventricular  at  the  base,  and  the  opening 
of  the  pulmonary  artery  also  at  the  base,  but  more  to  the  left ; 
the  part  of  the  ventricle  leading  to  it  is  called  the  conus  arteriosus 
or  infundibuium ;  both  orifices  are  guarded  by  valves,  the  former 
called  tricuspid  and  the  latter  semilunar  or  sigmoid.  In  this 
ventricle  are  also  the  projections  of  the  muscular  tissue  called 
columnee  carnece  (described  at  length  p.  135). 

Left  Auricle. — The  left  auricle  is  situated  at  the  left  and 
posterior  part  of  the  base  of  the  heart,  and  is  best  seen  from 
behind.  It  is  quadrilateral,  and  receives  on  either  side  two  pul- 
monary veins.  The  auricular  appendix  is  the  only  part  of  the 
auricle  seen  from  the  front,  and  corresponds  with  that  on  the 
right  side,  but  is  thicker,  and  the  interior  is  more  smooth.  The 
left  auricle  is  only  slightly  thicker  than  the  right,  the  difference 
being  as  1%  lines  to  1  line.  The  left  auriculo-ventricular  orifice 
is  oval,  and  a  little  smaller  than  that  on  the  right  side  of  the 
heart. 

There  is  a  slight  vestige  of  the  foramen  between  the  auricles, 
which  exists  in  foetal  life,  on  the  septum  between  them. 

Left  Ventricle. — Though  taking  part  to  a  comparatively  slight 
extent  in  the  anterior  surface,  the  left  ventricle  occupies  the  chief 
part  of  the  posterior  surface.  In  it  are  two  openings  very  close 
together,  viz.  the  auriculo-ventricular  and  the  aortic,  guarded  by 


i  H.\: 


CHAMBERS    OF    THE    BEART 


131 


the  valves  corresponding  to  th  the  right   Bide  of  ti 

viz.  the  bicuspid  or  mitral  and  the  semilunar  or 


Fig.  93. —  The  k/i  'ride  opened,  and  a  part  of  their  anterior  and 

removed.     A.— The  pulmonary  artery  has  been  divided  at  its  commencement  : 
opening  into  the  left  ventricle  carried  a  short  distance  into  the  aorta  between  two  of 
the  segments  of  the  semilunar  valves  :  and  the  left  part  of  the  auricle  with  its  appendix 
has  been  removed.  The  right  auricle  is  out  of  view.    1,  the  two  right  pulmonary  veins 
short ;  their  openings  are  seen  within  the  auricle ;  1 ' ,  placed  within  the  cavity  of  the  auricle 
on  the  left  side  of  the  septum  and  on  the  part  which  forms  the  remains  of  the  valve  of 
the  foramen  ovale,  of  which  the  crescentic  fold  is  seen  towards  the  left  hand  ■ 
2,  a  narrow  portion  of  the  wall  of  the  auricle  and  ventricle  preserved   roun  . 
auriculo-ventricular  orifice  ;  5.  5',  the  cut  surface  of  the  walls  of  the  ventricle,  seen  to 
become  very  much  thinner  towards  3 ",  at  the  ap-  1  the  anterior 

wall  of  the  left  ventricle  which  has  been  preserved  with  the  principal  anterior  columna 
carnea  or  musculus  papillaris  attached  to  it ;  5.  5,  musculi  papLL 
of  the  septum,  between  the  two  ventricles,  within  the  cavity  01  the  left  ventricle ; 
6,  6',  the  mitral  valve  ;  7,  placed  in  the  interior  of  the  aorta  near  its  commencement 
and  above  the  three  segments  of  its  semilunar  valve  which  axe  hanging  loosely  toge- 
ther ;  7',  the  exterior  of  the  great  aortic  sinus ;  8,  the  root  of-  the  pulmonary  artery 
and  its  semilunar  valves  ;  8',  the  separated  portion  of  the  pulmonary  artery  remaining 
attached  to  the  aorta  by  9,  the  cord  of  the  duct  sos;  10,  the  arteries  rising 

from  the  summit  of  the  aortic  arch  'Allen  Thomson, . 


132 


CIRCULATION    OF    THE    BLOOD. 


[chap.  v. 


Fig.  94. — Transverse  section  of  bullock'' s  heart  in 
a  state  of  cadaveric  rigidity.  «,  cavity  of 
left  ventricle,  b,  cavity  of  right  ventricle. 
(Dalton.) 


opening  is  at  the  left  and  back  part  of  the  base  of  the  ventricle, 
and  the  aortic  in  front  and  towards  the  right.      In  this  ventricle, 

as  in  the  right,  are  the  co- 
lumnar carnese,  which  are 
smaller  but  more  closely 
reticulated.  They  are  chiefly 
found  near  the  apex  and 
along  the  posterior  wall. 
They  will  be  again  referred 
to  in  the  description  of  the 
valves.  The  walls  of  the 
left  ventricle,  which  are 
nearly  half  an  inch  in  thick- 
ness, are,  wTith  the  exception 
of  the  apex,  twice  or  three  times  as  thick  as  those  of  the  right. 
Capacity  of  the  Chambers. — The  capacity  of  the  two  ven- 
tricles is  about  four  to  six  ounces  of  blood,  the  whole  of  which  is 
impelled  into  their  respective  arteries  at  each  contraction.  The 
capacity  of  the  auricles  is  rather  less  than  that  of  the  ventricles : 
the  thickness  of  their  walls  is  considerably  less.  The  latter 
condition  is  adapted  to  the  small  amount  of  force  which  the 
auricles  require  in  order  to  empty  themselves  into  their  adjoining 
ventricles ;  the  former  to  the  circumstance  of  the  ventricles  being 
partly  filled  with  blood  before  the  auricles  contract. 

Size  and  Weight  of  the  Heart.  —  The  heart  is  about  5 
inches  long,  3!  inches  greatest  wTidth,  and  2\  inches  in  its  extreme 
thickness.  The  average  weight  of  the  heart  in  the  adult  is  from 
9  to  10  ounces;  its  weight  gradually  increasing  throughout  life 
till  middle  age  ;  it  diminishes  in  old  age. 

Structure. — The  Avails  of  the  heart  are  constructed  almost 
entirely  of  layers  of  muscular  fibres ;  but  a  ring  of  connective 
tissue,  to  which  some  of  the  muscular  fibres  are  attached,  is  in- 
serted between  each  auricle  and  ventricle,  and  forms  the  boundary 
of  the  auriculo-ventricular  opening.  Fibrous  tissue  also  exists  at 
the  origins  of  the  pulmonary  artery  and  aorta. 

The  muscular  fibres  of  each  auricle  are  in  part  continuous  with 
those  of  the  other,  and  partly  separate ;  and  the  same  remark 
holds  true  for  the  ventricles.  The  fibres  of  the  auricles  are,  how- 
ever, quite  separate  from  those   of  the   ventricles,  the   bond  of 


(II  IP.  \ .  I 


STKrcTl'ltK    OF    T1IK    EtEART. 


133 


connection   between  them  being  onlj    the  fibrous  tissue  of  the 
auriculo-ventricular  openings. 


Fig.  95.—  Network  of  muscular  fibres  (striated)  from  the  heart  of  ;t  pig.    The  nuclei  of  the 
muscle-corpuscles  are  well  shown,     x  450.      (Klein  and  Noble  Smith.) 

The  muscular  fibres  of  the  heart,  unlike  those  of  most  of  the 
involuntary  muscles,  are  striated ;  but  although,  in  this  respect 
they  resemble  the  skeletal  muscles, 
they  have  distinguishing  characteris- 
tics of  their  own.  The  fibres  which 
lie  side  by  side  are  united  at  frequent 
intervals  by  short  brandies  (fig.  95). 
The  fibres  are  smaller  than  those  of 
the  ordinary  striated  muscles,  and 
their  striation  is  less  marked.  No 
sarcolemma  can  be  discerned.  The 
muscle-corpuscles  are  situate  in  the 
middle  of  the  substance  of  the  fibre  ; 
and  in  correspondence  with  these 
the  fibres  appear  under  certain  con- 
ditions subdivided  into  oblong  por- 
tions   or   "cells,"   the    offsets    from       ^'£SS^ fSA.f^ 


134 


CIRCULATION    OF    THE    BLOOD. 


[CHAP.   V. 


winch  are  the  means  by  which  the  fibres  anastomose  one  with 
another  (fig.  96). 

Endocardium.— As  the  heart  is  clothed  on  the  outside  by  a 
thm  transparent  layer  of  pericardium,  so  its  cavities  are  lined  by 
a  smooth  and  shining  membrane,  or  endocardium,  which  is  directly 
continuous  with  the  internal  lining  of  the  arteries  and  veins. 
The  endocardium  is  composed  of  connective  tissue  with  a  large 
admixture  of  elastic  fibres  ;  and  on  its  inner  surface  is  laid  down 
a  single  tessellated  layer  of  flattened  endothelial  cells.  Here  and 
there  unstriped  muscular  fibres  are  sometimes  found  in  the  tissue 
of  the  endocardium. 

Course  of  the  Blood  through  the  Heart.— The  arrange- 
ment of  the  heart's  valves  is  such  that  the  blood  can  pass  only 
in  one  direction,  and  this  is  as  follows  (fig.  97)  :— From  the  right 


Fig-  9T-— Din yia in  of  the  circulation  through  tht  heart  (Dalton). 


auricle  the  blood  passes  into  the  right  ventricle,  and  thence  into  the 
pulmonary  artery,  by  which  it  is  conveyed  to  the  capillaries  of  the 
lungs.  From  the  lungs  the  blood,  which  is  now  purified  and  altered 
in  colour,  is  gathered  by  the  pulmonary  veins  and  taken  to  the  left 
auricle.  From  the  left  auricle  it  passes  into  the  left  ventricle,  and 
thence  into  the  aorta,  by  which  it  is  distributed  to  the  capillaries 


chap,  v.]  VALVES    OF    THE    EEAET.  135 

of  every  portion  of  the  body.     The  branches  of  the  aorta,  from 
being  distributed  to  the  general  system,  are  called  spstt  mic  arterii 
and  from  these  the  blood  passes  into  the  systemic  capillaries,  where 
it  again  becomes  dark  and  impure,  and  thence  into  the  branch* 
of  the  systemic    veins,   which,  forming  by   their  union  two  lai 
trunks,  called  the  superior  and  inferior  vena  cava,  discharge  their 
contents  into  the  right  auricle,  whence  we  supposed  the  blood  to 
start 

The  Valves  of  the  Heart. — The  valve  between  the  righl 
auricle  and  ventricle  is  named  tricuspid  (5.  fig.  99),  because  it 
presents  thra  principal  cusps  or  subdivisions,  and  that  between 
the  left  auricle  and  ventricle  bicuspid  (or  mitral),  because  it  b 
two  such  portions  (6,  fig.  93).  But  in  both  valves  there  is  between 
each  two  principal  portions  a  smaller  one  ;  so  that  more  properly, 
the  tricuspid  may  be  described  as  consisting  of  six,  and  the  mitral 
«>1'  four,  ]K »it ions.  Eacli  portion  is  of  triangular  form,  its  apex  and 
sides  lying  free  in  the  cavity  of  the  ventricle,  and  its  base,  which 

oiitinuons  with  the  bases  of  the  neighbouring  portion  a  to 

form  an  annular  membrane  around  the  anriculo-ventrieular  open- 
ing, being  fixed  to  a  tendinous  ring  which  encircles  the  orifice 
between  the  auricle  and  ventricle  and  receives  the  insertions  of 
the  muscular  fibres  of  both.  In  each  principal  cusp  may  be 
distinguished  a  middle-piece,  extending  from  its  base  to  its  apex, 
and  including  about  half  its  width,  which  is  thicker,  and  much 
tougher  and  tighter  than  the  border-pieces  or  edges. 

AVhile  the  bases  of  the  several  portions  of  the  valves  are  fixed 
to  the  tendinous  rings,  their  ventricular  surfaces  and  borders  are 
fastened  by  slender  tendinous  fibres,  the  chorda:  tendinece,  to  the 
walls  of  the  ventricles,  the  muscular  fibres  of  which  project  into 
the  ventricular  cavity  in  the  form  of  bundles  or  columns  — the 
columnce  cameos.  These  columns  are  not  all  of  them  alike,  for 
while  some  of  them  are  attached  along  their  whole  length  on  one 
side,  and  by  their  extremities,  others  are  attached  only  by  their 
extremities  ;  and  a  third  set,  to  which  the  name  muscttli papillartt 
has  been  given,  are  attached  to  the  wall  of  the  ventricle  by  one 
extremity  only,  the  other  projecting,  pa] 'ilia-like,  into  the  cavity 
of  the  ventricle  (5,  fig.  93),  and  having  attached  to  it  chorda  ten- 
dinece.  of  the  tendinous  cords,  besides  those  which  pass  from  the 
walls  of  the  ventricle  and  the  musculi  papillares  to  the  margins  of 


!  36  CIRCULATION    OF    THE    BLOOD.  [chap.  v. 

the  valves,  there  are  some  of  especial  strength,  which  pass  from 
the  same  parts  to  the  edges  of  the  middle  and  thicker  portions  of 
the  cusps  before  referred  to.  The  ends  of  these  cords  arc  spread 
out  in  the  substance  of  the  valve,  giving  its  middle  piece  its  pecu- 
liar strength  and  toughness  ;  and  from  the  sides  numerous  other 
more  slender  and  branching  cords  arc  given  off,  which  are  attached 
all  over  the  ventricular  surface  of  the  adjacent  border-pieces  of  the 
principal  portions  of  the  valves,  as  well  as  to  those  smaller  portions 
which  have  been  mentioned  as  lying  between  each  two  principal 
ones.  Moreover,  the  musculi  papillares  are  so  placed  that,  from 
the  summit  of  each,  tendinous  cords  proceed  to  the  adjacent  halves 
of  two  of  the  principal  divisions,  and  to  one  intermediate  or 
smaller  division,  of  the  valve. 

The  preceding  description  applies  equally  to  the  mitral  and 
tricuspid  valve  ;  but  it  should  be  added  that  the  mitral  is  con- 
siderably thicker  and  stronger  than  the  tricuspid,  in  accordance 
with  the  greater  force  which  it  is  called  upon  to  resist. 

It  has  been  already  said  that  while  the  ventricles  communicate, 
on  the  one  hand,  with  the  auricles,  they  communicate,  on  the 
other,  with  the  large  arteries  which  convey  the  blood  away  from 
the  heart  ;  the  right  ventricle  with  the  pulmonary  artery  (6, 
fig.  93),  which  conveys  blood  to  the  lungs,  and  the  left  ventricle 
with  the  aorta,  which  distributes  it  to  the  general  system  (7, 
fig.  93).  And  as  the  auriculo-ventricular  orifice  is  guarded  by 
valves,  so  are  also  the  mouths  of  the  pulmonary  artery,  and  aorta 

(figs-  93>  99)- 

The    semilunar  valves,  three  in  number,   guard  the   orifice  of 

each  of  these  two  arteries.     They  are  nearly  alike  on  both  sides 

of  the   heart ;    but   those    of  the    aorta   are    altogether  thicker 

and    more    strongly  constructed  than    those    of  the    pulmonary 

artery,  in  accordance  with  the  greater  pressure  which  they  have 

to    withstand.      Each   valve    is    of  semilunar   shape,   its    convex 

margin  being  attached  to  a  fibrous  ring  at  the  place  of  junction 

of  the  artery  to  the  ventricle,  and  the  concave  or  nearly  straight 

border  being  free,  so  that  each  valve  forms  a  little  pouch  like 

a  watch-pocket   (7,  fig.  93).     In  the   centre  of  the  free  edge  of 

the  valve,  which  contains  a  fine  cord  of  fibrous  tissue,  is  a  small 

fibrous  nodule,  the  corjms  Arantii,  and  from  this  and  from  the 

attached  border  fine  fibres  extend  into  every  part  of  the  mid  sub- 


CHAP,  v.]  ACTION     OF    THE     II  i:\KT.  ^7 

Stance  Of    the  valve,  except   a  small    I  u  l  i;t  t  <  <  I    space  jusl     v,  itliin    1 1  n  ■ 

free  edge,  on  each  side  of  the  corpus  Arantii.  Here  the  valve  is 
thinnest,  and  composed  of  little  more  than  the  endocardium.  Tims 
constructed  and  attached,  the  three  semilunar  valves  are  placed 

side  by  side   around  the  arterial  orifice   of  each    ventricle,  SO   a-   to 

form  three  little  pouches,  which  can  he  separated  by  the  hlood 
passing  out  of  the  ventricle,  hut  which  immediately  afterwards  are 
pressed  together  so  as  to  prevent  any  return  (7,  rig-.  93,  and  7, 
fig.  99).  This  will  he  again  referred  to.  Opposite  each  of  the 
semilunar  cusps,  both  in  the  aorta  and  pulmonary  artery,  there  is 
a  bulging  outwards  of  the  wall  of  the  vessel  :  these  bulgings  are 
called  the  sinuses  of  Valsalva. 

Structure,  of  the  Valves. — The  valves  of  the  heart  are  formed 
essentially  of  thick  layers  of  closely  woven  connective  and  elastic 
tissue,  over  which,  on  every  part,  is  reflected  the  endocardium. 

The  Action  of  the  Heart. 

The  heart's  action  in  propelling  the  blood  consists  in  the  suc- 
cessive alternate  contraction  (systole)  and  relaxation  (diastole) 
of  the  muscular  walls  of  its  two  auricles  and  two  ventricles. 

Action  of  the  Auricles. — The  description  of  the  action  of  the 
heart  may  best  be  commenced  at  that  period  in  each  action  which 
immediately  precedes  the  beat  of  the  heart  against  the  side  of  the 
chest.  For  at  this  time  the  whole  heart  is  in  a  passive  state,  the 
walls  of  both  auricles  and  ventricles  are  relaxed,  and  their  cavities 
are  being  dilated.  The  auricles  are  gradually  filling  with  blood 
flowing  into  them  from  the  veins  ;  and  a  portion  of  this  blood 
passes  at  once  through  them  into  the  ventricles,  the  opening 
between  the  cavity  of  each  auricle  and  that  of  its  corresponding- 
ventricle  being,  during  all  the  pause,  free  and  patent.  The 
auricles,  however,  receiving  more  blood  than  at  once  passes 
through  them  to  the  ventricles,  become,  near  the  end  of  the  pause, 
fully  distended  ;  and  at  the  end  of  the  pause,  they  contract  and 
expel  their  contents  into  the  ventricles. 

The  contraction  of  the  auricles  is  sudden  and  very  quick  ;  it 
commences  at  the  entrance  of  the  great  veins  into  them,  and  is 
thence  propagated  towards  the  auriculo- ventricular  opening ;  but 
the  last  part   which  contracts   is  the  auricular   appendix.     The 


138  CIIICULATIOX    OF    THE    BLOOD.  [chap.  v. 

effect  of  this  contraction  of  the  auricles  is  to  quicken  the  flow  of 
blood  from  them  into  the  ventricles ;  the  force  of  their  contraction 
not  being  sufficient  under  ordinary  circumstances  to  cause  any 
back-flow  into  the  veins.  The  reflux  of  blood  into  the  great  veins 
is,  moreover,  resisted  not  only  by  the  mass  of  blood  in  the  veins  and 
the  force  with  which  it  streams  into  the  auricles,  but  also  by  the 
simultaneous  contraction  of  the  muscular  coats  with  which  the 
large  veins  are  provided  near  their  entrance  into  the  auricles. 
Any  slight  regurgitation  from  the  right  auricle  is  limited  also  by 
the  valves  at  the  junction  of  the  subclavian  and  internal  jugular 
veins,  beyond  which  the  blood  cannot  move  1  tack  wards  ;  and  the 
coronary  vein  is  preserved  from  it  by  a  valve  at  its  mouth. 

In  birds  and  reptiles  regurgitation  from  the  right  auricle  is  prevented  by 
valves  placed  at  the  entrance  of  the  great  vein-;. 

During  the  auricular  contraction  the  force  of  the  blood  pro- 
pelled into  the  ventricle  is  transmitted  in  all  directions,  but  being 
insufficient  to  separate  the  semilunar  valves,  it  is  expended  in 
distending  the  ventricle,  and,  by  a  reflux  of  the  current,  in  raising 
and  gradually  closing  the  auriculo-ventricular  valves,  which,  when 
the  ventricle  is  full,  form  a  complete  septum  between  it  and  the 
auricle. 

Action  of  the  Ventricles. — The  blood  which  is  thus  driven, 
by  the  contraction  of  the  auricles,  into  the  corresponding  ven- 
tricles, being  added  to  that  which  had  already  flowed  into  them 
during  the  heart's  pause,  is  sufficient  to  complete  their  diastole. 
Thus  distended,  they  immediately  contract  :  so  immediately, 
indeed,  that  their  systole  looks  as  if  it  were  continuous  with  that 
of  the  auricles.  The  ventricles  contract  much  more  slowly  than 
the  auricles,  and  in  their  contraction  probabty  always  thoroughly 
empty  themselves,  differing  in  this  respect  from  the  auricles,  in 
which,  even  after  their  complete  contraction,  a  small  quantity  of 
blood  remains.  The  shape  of  both  ventricles  during  systole 
undergoes  an  alteration,  the  left  probably  not  altering  in  length 
but  to  a  certain  degree  in  breadth,  the  diameters  in  the  plane  of 
the  base  being  diminished.  The  right  ventricle  does  actually 
shorten  to  a  small  extent.  The  systole  has  the  effect  of  diminish- 
ing the  diameter  of  the  base,  especially  in  the  plane  of  the  auriculo- 
ventricular  valves  ;  but  the  length  of  the  heart  as  a  whole  is  not 


CHAP.  V.]  IT.\(TI<>.\     OF    THE     IIKAltTS     YAI.YKS.  ,  yj 

altered.  (Ludwig.)  During  the  systole  of  the  ventricles,  boo,  the 
aorta  and  pulmonary  artery,  being  filled  wit  f  i  blood  by  the  force 
of  the  ventricular  action  against  considerable  resistance,  elongate 
as  well  us  expand,  and  the  whole  heart  moves  slightly  towards 
the  right  and  forwards,  twisting  <>n  its  Long  axis,  and  exposing 
inert'  of  the  left  ventricle  anteriorly  than  is  usually  in  front. 
When  the  systole  ends  the  heart  resumes  its  forme)-  position, 
rotating  to  the  left  again  as  the  aorta  and  pulmonary  artery 
contract. 

Functions  of  the  Auriculo-Ventricular  Valves. — The 
distension  of  the  ventricles  with  blood  continues  throughout  the 
whole  period  of  their  diastole.  The  auriculo-ventricular  valves 
are  gradually  brought  into  place  by  some  of  the  blood  getting 
behind  the  cusps  and  floating  them  up  ;  and  by  the  time  that  the 
diastole  is  complete,  the  valves  are  no  doubt  in  apposition,  the 
completion  of  this  being  brought  about  by  the  reflex  current 
caused  by  the  systole  of  the  auricles.  This  elevation  of  the 
auriculo-ventricular  valves  is,  no  doubt,  materially  aided  by  'the 
action  of  the  elastic  tissue  which  has  been  shown  to  exist  so 
largely  in  their  structure,  especially  on  the  auricular  surface.  At 
any  rate  at  the  commencement  of  the  ventricular  systole  they  are 
completely  closed.  It  should  be  recollected  that  the  diminution 
in  the  breadth  of  the  base  of  the  heart  in  its  transverse  diameters 
during  ventricular  systole  is  especially  marked  in  the  neighbour- 
hood of  the  auriculo-ventricular  rings,  and  thus  aids  in  rendering 
the  auriculo-ventricular  valves  competent  to  close  the  openings,  by 
greatly  diminishing  their  diameter.  The  margins  of  the  cusps  of 
the  valves  are  still  more  secured  in  apposition  with  another,  by 
the  simultaneous  contraction  of  the  musculi  papillares,  whose 
chordae  tendincae  have  a  special  mode  of  attachment  for  this 
object  (p.  136).  As  in  the  case  of  the  semilunar  valves  to  be 
immediately  described,  the  auriculo-ventricular  valves  meet  not 
by  their  edges  only,  but  by  the  opposed  surfaces  of  their  thin  outer 
borders.  The  semilunar  valves,  on  the  other  hand,  which  are 
closed  in  the  intervals  of  the  ventricle's  contraction  (fig.  92,  6),  are 
forced  apart  by  the  same  pressure  that  tightens  the  auriculo- 
ventricular  valves;  and,  thus,  the  whole  force  of  the  contracting 
ventricles  is  directed  to  the  expulsion  of  blood  through  the  aorta 
and  pulmonary  artery. 


140  CIRCULATION    OF    THE    BLOOD.  [chap.  V. 

The  form  and  position  of  the  fleshy  columns  on  the  internal 

walls  of  the  ventricle  no  douht  help  to  produce  this  obliteration  of 
the  cavity  during  their  contraction  ;  and  the  completeness  of  the 
closure  may  often  be  observed  on  making  a  transverse  section  of 
a  heart  shortly  after  death,  in  any  case  in  which  the  contraction 
of  the  ri'ior  mortis  is  very  marked  (fig.  94).  In  such  a  case  only 
a  central  fissure  may  be  discernible  to  the  eye  in  the  place  of  the 
cavity  of  each  ventricle. 

If  there  were  only  circular  fibres  forming  the  ventricular  wall, 
it  is  evident  that  on  systole  the  ventricle  would  elongate  ;  if  there 
were  only  longitudinal  fibres  the  ventricle  would  shorten  on 
systole  ;  but  there  are  both.  The  tendency  to  alter  in  length  is 
thus  counter-balanced,  and  the  whole  force  of  the  contraction  is 
expended  in  diminishing  the  cavity  of  the  ventricle  ;  or,  in  other 
words,  in  expelling  its  contents. 

On  the  conclusion  of  the  systole  the  ventricular  walls  tend  to 
expand  by  virtue  of  their  elasticity,  and  a  negative  pressure  is  set 
up,  which  tends  to  suck  in  the  blood.  This  negative  or  suctional 
pressure  on  the  left  side  of  the  heart  is  of  the  highest  importance 
in  helping  the  pulmonary  circulation.  It  has  been  found  to  be 
equal  to  23  mm.  of  mercury,  and  is  quite  independent  of  the 
aspiration  or  suction  power  of  the  thorax  in  aiding  the  blood-flow 
to  the  heart,  to  be  described  in  the  chapter  on  Respiration. 

Function  of  the  Musculi  Papillares. — The  special  function 
of  the  mv&nli  papillares  is  to  prevent  the  auriculo-ventricular 
valves  from  being  everted  into  the  auricle.  For  the  chorda? 
tendinea?  might  allow  the  valves  to  be  pressed  back  into  the 
auricle,  were  it  not  that  when  the  wall  of  the  ventricle  is  brought 
by  its  contraction  nearer  the  auriculo-ventricular  orifice,  the 
musculi  papillares  more  than  compensate  for  this  by  their  own 
contraction — holding  the  cords  tight,  and,  by  pulling  down  the 
valves,  adding  slightly  to  the  force  with  which  the  blood  is  expelled. 

What  has  been  said  applies  equally  to  the  auriculo-ventricular 
valves  on  both  sides  of  the  heart,  and  of  both  alike  the  closure  is 
generally  complete  every  time  the  ventricles  contract.  But  in 
some  circumstances  the  closure  of  the  tricuspid  valve  is  not 
complete,  and  a  certain  quantity  of  blood  is  forced  back  into  the 
auricle.  This  has  been  called  the  safety-valve  action  of  this  valve. 
The  circumstances  in  which  it  usually  happens  are  those  in  which 


chap.  v.|  SEMILUNAB    VALVES.  141 

the  vessels  of  the  lung  arc  al ready  full  enough  when  the  right 
ventricle  contracts,  as  <.;/.,  in  certain  pulmonary  diseases,  in  very 

active  exertion,  ami  in  great  efforts.  In  these  eases,  the  tricuspid 
valve  does  qoI  completely  close,  and  the  regurgitation  of  the  blood 
may  be  indicated  by  a  pulsation  in  the  jugular  veins  synchronous 
with  that  in  the  carotid  arteries. 

Function  of  the  Semilunar  Valves. — The  arterial  or  semi- 
lunar valves  are  forced  apart  by  the  out-streaming   blood,   with 
which  the  contracting  ventricle  dilates  the  large  arteries.     The 
dilation   of  the   arteries    is,   in    a   peculiar   manner,   adapted    to 
bring   the    valves    into    action.       The  lower   borders   of  the   semi- 
lunar valves   are   attached  to   the  inner  surface  of  a  tendinous 
ring,   which   is,   as    it   were,   inlaid   at  the   orifice   of  the   artery, 
between  the  muscular  fibres  of  the  ventricle  and  the  elastic  fibres 
of  the  walls  of  the  artery.      The  tissue  of  this  ring  is  tough,  and 
does  not  admit  of  extension  under  such  pressure  as  it  is  commonly 
exposed  to;  the  valves  are  equally  inextensile,  being,  as  already 
mentioned,   formed   of  tough,  close-textured,    fibrous  tissue,  with 
strong  interwoven  cords,  and  covered  with  endocardium.     Hence, 
when  the  ventricle  propels  blood  through  the  orifice  and  into  the 
canal    of  the    artery,    the  lateral    pressure  which  it   exercises   is 
sufficient  to  dilate   the  walls   of  the  artery,   but  not  enough   to 
stretch  in   an  equal  degree,  if  at  all,   the  unyielding  valves  and 
the    ring    to    which   their   lower    borders    are    attached.       The 
effect,    therefore,    of  each    such    propulsion    of   blood    from    the 
ventricle    is,    that  the    wall   of  the    first   portion    of  the    artery 
is  dilated  into  three  pouches  behind  the  valves,   while  the  free 
margins   of    the   valves    are    drawn   inward   towards    its    centre 
(fig.   98,  b).     Their  positions  may  be  explained  by  the  diagrams, 
in  which   the  continuous  lines  represent  a  transverse  section   of 
the    arterial    walls,    the    dotted    ones   the    edges    of   the    valves, 
firstly,  when  the  valves  are  nearest  to  the  walls  (a),  and,  secondly, 
when,  the  walls  being  dilated,  the  valves  are  drawn  away  from 
them  (b). 

This  position  of  the  valves  and  arterial  walls  is  retained  so  long 
as  the  ventricle  continues  in  contraction  :  but,  as  soon  as  it 
relaxes,  and  the  dilated  arterial  walls  can  recoil  by  their  elasticity, 
the  blood  is  forced  backwards  towards  the  ventricles  as  onwards  in 
the  course  of  the  circulation.     Part  of  the  blood  thus  forced  back 


142 


CIRCULATION  OF  THE  BLOOD. 


[chap.  v. 


lies  in  the  pouches  (sinuses  of  Valsalva)  (a,   fig.  98,  b)  between 
the  valves  and  the  arterial  walls ;  and  the  valves  are. by  it  pressed 


Fig.  98. — Sections  of  aorta,  to  show  the  action  of  the  semilunar  valves.  A  is  intended  to 
show  the  valves,  represented  by  the  dotted  lines,  pressed  towards  the  arterial  walls, 
represented  by  the  continuous  outer  line,  b  (after  Hunter)  shows  the  arterial  wall 
distended  into  three  pouches  («),  and  drawn  away  from  the  valves,  which  are 
straightened  into  the  fomi  of  an  equilateral  triangle,  as  represented  by  the  dotted 
lines. 

together  till  their  thin  lunated  margins  meet  in  three  lines  ra- 
diating from  the  centre  to  the  circumference  of  the  artery  (7  and  8, 
fig.  99). 


Fig.  99. — Vieto  of  the  base  of  the  ventricular  part  oftfu  heart,  showing  the  relative  position 
of  the  arterial  and  auriculo-ventricular  orifices. — §.  The  muscular  fibres  of  the  ven- 
tricles are  exposed  by  the  removal  of  the  pericardium,  fat,  blood-vessels,  etc. ;  the 
pulmonary  artery  and  aorta  have  been  removed  by  a  section  made  immediately 
beyond  the  attachment  of  the  semilunar  valves,  and  the  auricles  have  been  removed 
immediately  above  the  auriculo-ventricular  orifices.  The  semilunar  and  auriculo- 
ventricular  "valves  are  in  the  nearly  closed  condition,  i,  i,  the  base  of  the  right  ven- 
tricle ;  1',  the  conus  arteriosus  ;  2,  2,  the  base  of  the  left  ventricle  ;  3,  3,  the  divided 
wall  of  the  right  auricle  ;  4,  that  of  the  left ;  5,  5',  5",  the  tricuspid  valve  :  6,  6',  the 
mitral  valve.  In  the  angles  between  these  segments  are  seen  the  smaller  frii 
frequently  observed  ;  7,  the  anterior  part  of  the  pulmonary  artery  ;  8,  placed  upon 
the  posterior  part  of  the  root  of  the  aorta  ;  9,  the  right,  9',  the  left  coronary  artery. 
(Allen  Thomson.) 

The   contact  of  the  valves  in  this  position,  and  the  complete 
closure  of  the   arterial  orifice,  are  secured   by  the  peculiar   con- 


chap,  v.l  SEMILUNAR    VALVES. 


143 


BtructioD  of  their  borders   before   mentioned.     Amoi  sords 

which  are  interwoven  in  the  substance  of  the  valves,  are  two  of 
greater  strength  and  prominence  than  the  real  ;  of  which  one 
extends  along  the  free  border  of  each  valve,  and  the  other  forma 
a  double  curve  or  festoon  just  below  the  free  border.  Each  of 
these  cords  is  attached  by  its  outer  extremities  to  the  outer  end 
of  the  tree  margin  of  its  valve,  and  in  the  middle  to  the  corpus 
Arantii  ;  they  thus  enclose  a  lunated  space  from  a  line  to  a  line 
and  a  half  in  width,  in  which  space  the  substance  of  the  valve  is 

much  thinner  and  more  pliant   than   elsewhere.      When  the  valves 

are  pressed  down,  all  these  parts  or  spaces  of  their  surfaces  come 

into  contact,  and  the  closure  of  the  arterial  orifice  is  thus  secured 
by  the  apposition  not  of  the  mere  ed'^s  of  the  valves,  but  of  all 

those  thin  lunated  parts  of  each  which  lie  between  the  free  c    _ 
and  the  cords  next  below  them      These  parts  are  firmly  pr- 
_   ther,  and  the  greater  the  pressure  that  falls  on  them  thee 
and  more  secure  is  their  apposition.     The  corpora  Arantii  meet  at 


Fig.  100. —  I  turn  through  the  aorta  at   its   junction  with  the  left  ventricle,     a. 

Section  of  aorta,     bb,  Section  of  two  valves,    c,  Section  of  wall  of  ventricle. 
Internal  surface  of  ventricle. 

the  centre  of  the  arterial  orifice  when  the  valves  are  down,  and 
they  probably  assist  in  the  closure;  but  they  are  not  essential  to 
it,  for,  not  unfrequently,  they  are  wanting  in  the  valves  of  the  pul- 
monary artery,  which  are  then  extended  in  larger,  thin,  flapping 
margins.  In  valves  of  this  form,  also,  the  inlaid  cords  are  less 
distinct  than  in  those  with  corpora  Arantii ;  yet  the  closure  by 
contact  of  their  surfaces  is  not  less  secure. 


144 


CIRCULATION    OF    THE    BLOOD.  [chap.  v. 


It  has  been  clearly  shown  that  this  pressure  of  the  blood  is  not 
entirely  sustained  by  the  valves  alone,  but  in  part  by  the  muscular 
substance  of  the  ventricle  (Savory).  By  making  vertical  sections  (fig. 
ioo)  through  various  parts  of  the  tendinous  rings  it  is  possible  to 
show  clearly  that  the  aorta  and  pulmonary  artery,  expanding  towards 
their  termination,  are  situated  upon  the  outer  edge  of  the  thick 
upper  border  of  the  ventricles,  and  that  consequently  the  portion 
of  each  .semilunar  valve  adjacent  to  the  vessel  passes  over  and 
rests  upon  the  muscular  substance — being  thus  supported,  as  it 
were,  on  a  kind  of  muscular  floor  formed  by  the  upper  border  of 
the  ventricle.  The  result  of  this  arrangement  is  that  the  reflux 
of  the  blood  is  most  efficiently  sustained  by  the  ventricular  wall.* 

As  soon  as  the  auricles  have  completed  their  contraction  they 
begin  again  to  dilate,  and  to  be  refilled  with  blood,  which  flows 
into  them  in  a  steady  stream  through  the  great  venous  trunks. 
They  are  thus  filling  during  all  the  time  in  which  the  ventricles 
are  contracting:  and  the  contraction  of  the  ventricles  being  ended, 
these  also  again  dilate,  and  receive  again  the  blood  that  flows  into 
them  from  the  auricles.  By  the  time  that  the  ventricles  are  thus 
from  one-third  to  two-thirds  full,  the  auricles  are  distended ; 
these,  then  suddenly  contracting,  fill  up  the  ventricles,  as  already 
described  (p.  137). 

Cardiac  Revolution. — If  we  suppose  a  cardiac  revolution 
divided  into  five  parts,  one  of  these  will  be  occupied  by  the  con- 
traction of  the  auricles,  two  by  that  of  the  ventricles,  and  two  by 
repose  of  both  auricles  and  ventricles. 

Contraction  of  Auricles     .     .     .     1  +   Kepose  of  Auricles  .     .     .4  =  5 

„  Ventricles       .     .     2  +         .,  Ventricles     .     .3  =  5 

Kepose  (no  contraction  of  either 

auricles  or  ventricles)     .     .     .     2  +   Contraction  (of  either  auri- 

—  cles  or  ventricles)     .     -3  =  5 

5 

If  the  speed  of  the  heart  be  quickened,  the  time  occupied  by 
each  cardiac  revolution  is  of  course  diminished,  but  the  diminution 
affects  only  the  diastole  and  pause.     The  systole  of  the  ventricles 


*  Savory's  preparations,  illustrating  this  and  other  points  in  relation 
to  the  structure  and  functions  of  the  valves  of  the  heart,  are  in  the  Museum 
of  St.  Bartholomew's  Hospital. 


chap,  v.]  SOUNDS    OF    THE    HEART.  145 

occupies  very  much  the  same  time,  aboul  /,,  Bee,  whatever  the 
pulse-rate. 

The  periods  in  which  the  several  valves  of  the  heart   are   In 
action  may  be  connected  with  the  foregoing  table  \  for  the  auriculo- 

ventrieular  valves  are  closed,  and  the  arterial  valves  are  open 
during  the  whole  time  of  the  ventricular  contraction,  while, 
during   the   dilation  and  distension  of  the  ventricles  the  latter 

valves  are   shut,  the  former  open.      Thus  whenever   the  auriculo- 
ventrienlar   valves   are   open,  the    arterial    valves    are    closed    and 
id. 


Sounds   of  the  Heart. 

When  the  ear  is  placed  over  the  region  of  the  heart,  two  sounds 

may  he  heard  at  every  beat  of  the  heart,  which  follow  in  quick 
cession,  and  are  succeeded  by  a  pause  or  period  of  silence. 
The  first  sound  is  dull  and  prolonged ;  its  commencement  coincides 
with  the  impulse  of  the  heart,  and  just  precedes  the  pulse  at  the 
wrist.  The  second  is  a  shorter  and  sharper  sound,  with  a  some- 
what flapping  character,  and  follows  close  after  the  arterial  pulse. 
The  period  of  time  occupied  respectively  by  the  two  sounds  taken 
together,  and  by  the  pause,  are  almost  exactly  equal.  The  rela- 
tive length  of  time  occupied  by  each  sound,  as  compared  with  the 
other,  is  a  little  uncertain.  The  difference  may  be  best  appre- 
ciated by  considering  the  different  forces  concerned  in  the  pro- 
duction of  the  two  sounds.  In  one  case  there  is  a  strong,  compa- 
ratively slow,  contraction  of  a  large  mass  of  muscular  fibres,  urging 
forward  a  certain  quantity  of  fluid  against  considerable  resistance ; 
while  in  the  other  it  is  a  strong  but  shorter  and  sharper  recoil  of 
the  elastic  coat  of  the  large  arteries, — shorter  because  there  is  no 
resistance  to  the  flapping  back  of  the  semilunar  valves,  as  there 
was  to  their  opening.  The  sounds  may  be  expressed  by  saying 
the  words  lubb — dup  (C.  J.  B.  Williams). 

The  events  which  correspond,  in  point  of  time,  with  the  first 
sound,  are  (1)  the  contraction  of  the  ventricles.  (2)  the  first  part. 
of  the  dilatation  of  the  auricles,  (3)  the  closure  of  the  auriculo- 
ventricular  valves,  (4)  the  opening  of  the  semilunar  valves,  and 
(5)  the  propulsion  of  blood  into  the  arteries.  The  sound  is  suc- 
ceeded, in  about  one-thirtieth  of  a  second,  by  the  pulsation  of  the 


146  CIRCULATION    OF    THE    BLOOD.  [chap.  v. 

facial  arteries,  and  in  about  one-sixth  of  a  second,  by  the  pulsa- 
tion of  the  arteries  at  the  wrist.  The  second  sound,  in  point  of 
time,  immediately  follows  the  cessation  of  the  ventricular  con- 
traction, and  corresponds  with  (a)  the  closure  of  the  semilunar 
valves,  (b)  the  continued  dilatation  of  the  auricles,  (c)  the  commenc- 
ing dilatation  of  the  ventricles,  and  (d)  the  opening  of  the  auriculo- 
ventricular  valves.  The  %>ause  immediately  follows  the  second 
sound,  and  corresponds  in  its  first  x>art  with  the  completed  disten- 
sion of  the  auricles,  and  in  its  second  with  their  contraction,  and 
the  completed  distension  of  the  ventricles  ;  the  auriculo-ventricular 
valves  being,  all  the  time  of  the  pause,  open,  and  the  arterial 
valves  closed. 

Causes. —  The  chief  cause  of  the  first  sound  of  the  heart 
appears  to  be  the  vibration  of  the  auriculo-ventricular  valves,  due 
to  their  stretching,  and  also,  but  to  a  less  extent,  of  the  ventricular 
walls,  and  coats  of  the  aorta  and  pulmonary  artery,  all  of  which 
parts  are  suddenly  put  into  a  state  of  tension  at  the  moment  of 
ventricular  contraction.  The  effect  may  be  intensified  by  the 
muscular  sound  produced  by  contraction  of  the  mass  of  muscular 
fibres  which  form  the  ventricle. 

The  cause  of  the  second  sound  is  more  simple  than  that  of  the 
first.  It  is  probably  due  entirely  to  the  sudden  closure  and  conse- 
quent vibration  of  the  semilunar  valves  when  they  are  pressed 
down  across  the  orifices  of  the  aorta  and  pulmonary  artery.  The 
influence  of  the  valves  in  producing  the  sound  is  illustrated  by 
the  experiment  performed  on  large  animals,  such  as  calves,  in 
which  the  results  could  be  fully  appreciated.  In  these  experi- 
ments two  delicate  curved  needles  were  inserted,  one  into  the 
aorta,  and  another  into  the  pulmonary  artery,  below  the  line  of 
attachment  of  the  semilunar  valves,  and,  after  being  carried 
upwards  about  half  an  inch,  were  brought  out  again  through  the 
coats  of  the  respective  vessels,  so  that  in  each  vessel  one  valve 
was  included  between  the  arterial  walls  and  the  wire.  Upon 
applying  the  stethoscope  to  the  vessels,  after  such  an  operation, 
the  second  sound  had  ceased  to  be  audible.  Disease  of  these 
valves,  when  so  extensive  as  to  interfere  with  their  efficient 
action,  also  often  demonstrates  the  same  fact  by  modifying  or 
destroying  the  distinctness  of  the  second  sound. 

One  reason  for  the  second  sound  being  a  clearer  and  sharper 


chap,  v.]       SOUNDS    AND    [MPTJLSE    OF    THE    BEABT.  14- 

one  than  the  firet  may   be,  that  the   semilunar  valves  arc    n<,t 
covered  in  by  the  thick   layer  of  fibres  composing  the  walls  of 
the  heart  to  such   an  extent   as  arc  the  auricukhventricular.     It 
might  be  expected  therefore  that  their  vibration  would   be  more 

sily  heard  through  a  stethoscope  applied  to  the  walls  of  the 
chest. 

The  contraction  of  the  auricles  which  takes  place  in  the  end  of 
the  pause  is  inaudible  outside  the  chest,  but  may  be  heard,  when 
the  heart  is  exposed  ami  tic  stethoscope  placed  on  it,  as  a  slight 
sound  preceding  and  continued  into  the  louder  sound  of  the  ven- 
tricular contraction. 

The  Impulse  of  the  Heart. — At  the  commencement  of  each 
ventricular  contraction,  the  heart  maybe  felt  to  beat  "with  a  slight 
shock  or  impulse  against  the  walls  of  the  chest.  The  force  of  the 
impulse,  and  the  extent  to  which  it  may  be  perceived  beyond  this 
point,  vary  considerably  in  different  individuals,  and  in  the  same 
individual  under  different  circumstances.  It  is  felt  more  distinctly, 
and  over  a  larger  extent  of  surface,  in  emaciated  than  in  fat  and 
robust  persons,  and  more  during  a  forced  expiration  than  in  a  deep 
inspiration  ;  for,  in  the  one  case,  the  intervention  of  a  thick  layer 
of  fat  or  muscle  between  the  heart  and  the  surface  of  the  chest, 
and  in  the  other  the  inflation  of  the  portion  of  lung  which  over- 
laps the  heart,  prevents  the  impulse  from  being  fully  transmitted 
to  the  surface.  An  excited  action  of  the  heart,  and  especially  a 
hypertrophied  condition  of  the  ventricles,  will  increase  the  impulse  ; 
while  a  depressed  condition,  or  an  atrophied  state  of  the  ventricular 
walls,  will  diminish  it. 

Cause  of  the  Impulse. — During  the  period  which  precedes 
the  ventricular  systole,  the  apex  of  the  heart  is'situated  upon  the 
diaphragm  and  against  the  chest-wall  in  the  fifth  intercostal  space. 
When  the  ventricles  contract,  their  walls  become  hard  and  tense, 
since  to  expel  their  contents  into  the  arteries  is  a  distinctly  labo- 
rious action,  as  it  is  resisted  by  the  tension  within  the  vessels.  It 
is  to  this  sudden  hardening  that  the  impulse  of  the  heart  against 
the  chest-wall  is  due,  and  the  shock  of  the  sudden  tension  may  be 
felt  not  only  externally,  but  also  internally,  if  the  abdomen  of  an 
animal  be  opened  and  the  finger  be  placed  upon  the  under  surface 
of  the  diaphragm,  at  a  point  corresponding  to  the  under  surface 
of  the  ventricle.     The  shock  is  felt,  and  possibly  seen  more  dis- 

L   2 


148 


CIRCULATION    OF    THE    BLOOD. 


[chap.  v. 


tinctly  because  of  the  partial  rotation  of  the  heart,  already 
spoken  of,  along  its  long  axis  towards  the  right.  The  move- 
ment produced  by  the  ventricular  contraction  may  be  registered 
by  means  of  an  instrument  called  the  cardiograph,  and  it  will 
be  found  to  correspond  almost  exactly  with  a  tracing  obtained 
by  the  same  instrument  applied  over  the  contracting  ventricle 
itself. 

The  Cardiograph  (fig.  101)  consists  of  a  cup-shaped  metal  box 
over  the  open  front  of  which  is  stretched  an  elastic  membrane  upon 


Fig.  101. — Cardiograph.     (Sanderson's. 


which  is  fixed  a  small  knob  of  hard  wood  or  ivory.  This  knob, 
however,  may  be  attached  instead,  as  in  the  figure,  to  the  side  of 
the  box  by  means  of  a  spring,  and  may  be  made  to  act  upon  a 
metal  disc  attached  to  the  elastic  membrane. 

The  knob  (a)  is  for  application  to  the  chest-wall  over  the  place 
of  the  greatest  impulse  of  the  heart.  The  box  or  tympanum  com- 
municates by  means  of  an  air-tight  elastic  tube  (/)  with  the 
interior  of  a  second  tympanum  (fig.  102,  b),  in  connection  with 
which  is  a  long  and  light  lever  (a).  The  shock  of  the  heart's 
impulse  being  communicated  to  the  ivory  knob,  and  through  it 
to  the  first  tympanum,  the  effect  is,  of  course,  at  once  transmitted 
by  the  column  of  air  in  the  elastic  tube  to  the  interior  of  the 
second  tympanum,  also  closed,  and  through  the  elastic  and  mov- 
able lid  of  the  latter  to  the  lever,  which  is  placed  in  connection 


chap,  v.]  CARDIOGRAPH.  149 

with  a  registering  apparatus,  which  cod  aerally  of  a  cylinder 

or  dram  covered  with  smoked  pi  solving  aooording 


b  .  tn  which  the  movement  of  the  column  of  air  in  the  first 
tympanum  is  conducted  by  the  tube,  '.  and  from  which  it  is  communicated  by  the 
lever,  '7,  to  a  revolving  cylinder,  so  that  the  tracing  of  the  movement  of  the  impulse 
beat  is  obtained. 

definite  velocity  by  clock-work.  The  point  of  the  lever  writes 
upon  the  paper,  and  a  tracing  of  the  hearts  impulse  is  thus 
obtained. 

B}'  placing  three  small  india-rubber  air-bags  in  the  interior  respec- 
tively of  the  right  auricle,  the  right  ventricle,  and  in  an  intercostal 


Fig.  103. —  Tracing  0/ the  impulse  <>j  tUt  heart  of  m  i         Maiey.] 

space  in  front  of  the  heart  of  living  animals  (horse),  and  placing  these 
bags,  by  means  of  long  narrow  tubes,  in  communication  with  three 
levers,  arranged  one  over  the  other  in  connection  with  a  registering 
apparatus  (fig.  104),  MM.  Chauveau  and  Marey  have  been  able  to 
measure  with  much  accuracy  the  variations  of  the  endocardial 
pressure  and  the  comparative  duration  of  the  contractions  of  the 
auricles  and  ventricles.  By  means  of  the  same  apparatus,  the 
synchronism  of  the  impulse  with  the  contraction  of  the  ventricles,  is 
also  well  shown  ;  and  the  causes  of  the  several  vibrations  of  which 
it  is  really  composed,  have  been  discovered 


i;o 


CIRCULATION    OF    THE    BLOOD. 


[(HAP.  V 


In  the  tracing  (fig   105),  the  intervals  between  the  vertical  lines 
represent  periods  of  a  tenth  of  a  second.     The  parts  on  which  any 


Fig.  104. — Apparatus  of  MM.  Chan  vau  and  Marey  for  estimating  the  variations  of  endo- 
cardial pressure,  and  production  of  impulse  of  the  heart. 

given  vertical  line  foils  represent,  of  course,  simultaneous  events. 
Thus. — it  will  be  seen  that  the  contraction  of  the  auricle,  indicated 
bj  the  upheaval  of  the  tracing  at  A  in  first  tracing,  causes  a  slight 
increase  of  pressure  in  the  ventricle  (a'  in  second  tracing),   and 


Fig.  10;. —  Tracings  of  (i),  Intra-aurieular,  and  [2),  Tntra-ventricular  pressures,  and  (3), 
of  the  impulse  of  the  heart,  to  he  read  from  left  to  right,  obtained  by  Chauveauand 
Marey's  apparatus. 

produces  a  tiny  impulse  (a"  in  third  tracing).  So  also,  the 
closure  of  the  semilunar  valves,  while  it  causes  a  momentarily 
increased  pressure  in  the  ventricle  at  d',  does  not  fail  to  affect 


chap,  v.]       FREQUENCY    OF    THE    HEART'S    ACTION. 


151 


the  pressure  in  the  auricle  i>,  and  to  leave  its  mark  in  the  tracing 

of  the  impulse  also,  i>  . 

The  large  upheaval  <»f  the  ventricular  and  the  impulse  traci 
between  a' and  \<\  and  a."  and  d",  are  caused  by  the  ventricular 
i-  infraction,  while  the  smaller  undulations,  between  b  and  1 .  B'and 
c',  b"  and  c",  are  caused   by  the  vibrations  consequent  on   the 
tightening  and  closure  of  the  auriculo-ventricular  valves. 

Although,  ii<>  doubt,  the  method  thus  described  may  show  a 
perfectly  correct  view  of  the  endo-cardiac  pressure  variations,  it 
should  he  recollected  that  the  muscular  walls  may  grip  the  air- 
.  'Ven  after  the  complete  expulsion  of  the  contents  of  the 
chamber,  ami  bo  the  lever  might  remain  for  a  too  long  time  in  the 
position  of  extreme  tension,  and  would  represent  on  the  tracing 
not  only,  as  it  ought  to  do,  the  auricular  or  ventricular  pressure  on 
the  blood,  but,  also  afterwards,  the  muscular  pressure  exerted 
upon  the  bags  themselves.     (M.  Foster.) 

Frequency  and.  Force  of  the  Heart's  Action. 

The  heart  of  a  healthy  adult  man  contracts  from  seventy  to 
seventy-five  times  in  a  minute  ;  but  many  circumstances  cause 
this  rate,  which  of  course  corresponds  with  that  of  the  arteria 
pulse,  to  vary  even  in  health.  The  chief  are  age,  temperament, 
sex,  food  and  drink,  exercise,  time  of  day,  posture,  atmospheric 
pressure,  temperature. 

Age. — The  frequency  of  the  heart's  action  gradually  diminishes  from  the 
commencement  to  near  the  end  of  life,  but  is  said  to  rise  again  somewhat 
iu  extreme  old  age,  thus  : — 

Before  birth  the  average  number  of  pulses  in  a  minute  is  150 

Just  after  birth from  140  to  130 

During  the  first  year 

During  the  second  year  .         .... 

During  the  third  year 

About  the  seventh  year  .         .         .         .         .     . 

About  the  fourteenth  year,  the  average  number 
of  pulses  in  a  minute  is  frorn  .... 

In  adult  age 

In  old  age 

In  decrepitude 

Temperament  and  See. — In  persons  of  sanguine  temperament,  the  heart 


130  to 

"5 

115  to 

100 

100  to 

90 

90  to 

S5 

85  to 

So 

So  to 

70 

70  to 

60 

75  to 

65 

I52  CIRCULATION    OF    THE    BLOOD.  [chap.  V. 

acts  somewhat  more  frequently  than  in  those  of  the  phlegmatic  ;  and  in  the 
female  sex  more  frequently  than  in  the  male. 

Food  and  Brink.  Exercise. — After  a  meal  its  action  is  accelerated,  and 
still  more  so  during  bodily  exertion  or  mental  excitement ;  it  is  slower 
during  sleep. 

Diurnal  Variation. — It  appears  that,  in  the  state  of  health,  the  pulse  is 
most  frequent  in  the  morning,  and  becomes  gradually  slower  as  the  day 
advances  :  and  that  this  diminution  of  frequency  is  both  more  regular  and 
more  rapid  in  the  evening  than  in  the  morning. 

Posture. — It  is  found  that,  as  a  general  rule,  the  pulse,  especially  in  the 
adult  male,  is  more  frequent  in  the  standing  than  in  the  sitting  posture,  and 
in  the  latter  than  in  the  recumbent  position  ;  the  difference  being  greatest 
between  the  standing  and  the  sitting  posture.  The  effect  of  change  of 
posture  is  greater  as  the  frequency  of  the  pulse  is  greater,  and,  accordingly, 
is  more  marked  in  the  morning  than  in  the  evening.  By  supporting  the 
body  in  different  postures,  without  the  aid  of  muscular  effort  of  the  indi- 
vidual, it  has  been  proved  that  the  increased  frequency  of  the  pulse  in  the 
sitting  and  standing  positions  is  dependent  upon  the  muscular  exertion 
engaged  in  maintaining  them  ;  the  usual  effect  of  these  postures  on  the  pulse 
being  almost  entirely  prevented  when  the  usually  attendant  muscular  exer- 
tion was  rendered  unnecessary.     (Guy.) 

Atmospheric  Pressure. — The  frequency  of  the  pulse  increases  in  a  cor- 
responding ratio  with  the  elevation  above  the  sea. 

Temperature . — The  rapidity  and  force  of  the  heart's  contractions  are 
largely  influenced  by  variations  of  temperature.  The  frog's  heart,  when 
excised,  ceases  to  beat  if  the  temperature  be  reduced  to  320  F.  (0°  C).  When 
heat  is  gradually  applied  to  it,  both  the  speed  and  force  of  the  heart's  con- 
tractions increase  till  they  reach  a  maximum.  If  the  temperature  is  still 
further  raised,  the  beats  become  irregular  and  feeble,  and  the  heart  atlength 
stands  still  in  a  condition  of  "  heat-rigor." 

Similar  effects  are  produced  in  warm-blooded  animals.  In  the  rabbit, 
the  number  of  heart-beats  is  more  than  doubled  when  the  temperature  of 
the  air  was  maintained  at  1050  F.  (400,5  C).  At  1130 — 1140  F.  (450  C),  the 
rabbit's  heart  ceases  to  beat. 


Eelative  Frequency  of  the  Pulse  to  that  of  Respiration. 

— In  health  there  is  observed  a  nearly  uniform  relation  between 
the  frequency  of  the  pulse  and  of  the  respirations ;  the  proportion 
being,  on  an  average,  one  respiration  to  three  or  four  beats  of 
the  heart.  The  same  relation  is  generally  maintained  in  the 
cases  in  which  the  pulse  is  naturally  accelerated,  as  after  food  or 
exercise ;  but  in  disease  this  relation  usually  ceases.  In  many 
affections  accompanied  with  increased  frequency  of  the  pulse,  the 
respiration  is,  indeed,  also  accelerated,  yet  the  degree  of  its  accele- 
ration may  bear  no  definite  proportion  to  the  increased  number  of 
the  heart's  actions  :  and  in  many  other  cases,  the  pulse  becomes 
more  frequent  without  any  accompanying  increase  in  the  number 


ohap.  v.]  FORCE    OF    THE    HEARTS    ACTION  153 

of  respirations  ;  or,  the  respiration  alone  may  l>e  accelerated,  the 
Qumber  of  pulsations  remaining  stationary,  or  even  falling  below 

the  ordinary  standard. 

The  Force  of  the  Ventricular  Systole  and  Diastole.— 
The  fora  of  the  left  ventricular  systole  is  more  than  double  thai 
exerted  by  the  contraction  of  the  right:  this  difference  in  the 
amount  of  force  exerted  by  the  contraction  of  the  two  ventricL 
results  from  the  walls  of  the  left  ventricle  being  about  twice  or 
three  times  as  thick  as  those  of  the  right.  And  the  difference  is 
adapted  to  the  greater  degree  of  resistance  which  the  left  ventricle 
has  to  overcome,  compared  with  that  to  be  overcome  by  the  right: 
the  former  having  to  propel  blood  through  every  part  of  the  body, 
the  latter  only  through  the  lungs. 

The  actual  amount  of  the  intra-ventricular  pressures  during  systole 
in  the  dog  has  been  found  to  be  2-4  inches  (60  mm.)  of  mercury 
in  the  right  ventricle,  and  6  inches  (150  mm.)  in  the  left.  During 
diastole  there  is  in  the  right  ventricle  a  negative  or  suction  pres- 
sure of  about  f  of  an  inch  (-  17  to  —  16  mm.),  and  in  the  left 
ventricle  from  2  inches  to  ±  of  an  inch  (  —  52  to  —  20  mm.).  Part 
of  this  fall  in  pressure,  and  possibly  the  greater  part,  is  to  be 
referred  to  the  influence  of  respiration;  but  without  this  the 
negative  pressure  of  the  left  ventricle  caused  by  its  active  dilata- 
tion is  about  4  of  an  inch  (23  mm.)  of  mercury. 

The  right  ventricle  is  undoubtedly  aided  by  this  suction  power 
of  the  left,  so  that  the  whole  of  the  work  of  conducting  the 
pulmonary  circulation  does  not  fall  upon  the  right  side  of  the 
heart,  but  is  assisted  by  the  left  side. 

The  Force  of  the  Auricular  Systole  and  Diastole.— 
The  maximum  pressure  within  the  right  auricle  is  about  |-  of 
an  inch  (20  mm.)  of  mercury,  and  is  probably  somewhat  less  in 
the  left.  It  has  been  found  that  during  diastolo  the  pressure 
within  both  auricles  sinks  considerably  below  that  of  the  atmo- 
sphere ;  and  as  some  fall  in  pressure  takes  place,  even  when  the 
thorax  of  the  animal  operated  upon  has  been  opened,  a  certain 
proportion  of  the  fall  must  be  due  to  active  auricular  dilatation 
independent  of  respiration.  In  the  right  auricle,  this  negative 
pressure  is  about  —  10  mm. 

Work  Done  by  the  Heart.^In  estimating  the  work  done 
by  any  machine  it  is  usual  to  express  it  in  terms  of  the  "  unit  of 


154  CIRCULATION    OF    THE    BLOOD.  [chap.  v. 

work."  The  unit  of  work  is  defined  to  be  the  energy  expended 
in  raising  a  unit  of  weight  (i  lb.)  through  a  unit  of  height  (i  ft.). 
In  England,  the  unit  of  work  is  the  " foot-pound"  in  France,  the 
ii  hUograffnmetre." 

The  work  done  by  the  heart  at  each  contraction  can  be  readily 
found  by  multiplying -the  weight  of  blood  expelled  by  the  ventricles 
by  the  height  to  which  the  blood  rises  in  a  tube  tied  into  an 
artery.  This  height  was  found  to  be  about  9  ft.  in  the  horse,  and 
the  estimate  is  nearly  correct  for  a  largo  artery  in  man.  Taking 
the  weight  of  blood  expelled  from  the  left  ventricle  at  each 
systole  as  6  oz.,  i.e.,  f  lb.,  we  have  9  x  §  =  3*375  foot-pounds  as 
the  work  done  by  the  left  ventricle  at  each  systole  ;  and  adding 
to  this  the  work  done  by  the  right  ventricle  (about  one-third 
that  of  the  left)  we  have  3*375  x  1-125  =  4-5  foot-pounds  as  the 
work  done  by  the  heart  at  each  contraction.  Other  estimates  give 
\  kilogrammetre,  or  about  3!  foot-pounds.  Haughton  estimates 
the  total  work  of  the  heart  in  24  hours  as  about  124  foot-tons. 

Influence  of  the  Nervous  System  on  the  Action  of  the 
Heart. — The  hearts  of  warm-blooded  animals  cease  to  beat  almost 
if  not  quite  immediately  after  removal  from  the  body,  and  are, 
therefore,  unfavourable  for  the  study  of  the  nervous  mechanism 
which  regulates  their  action.  Observations  have,  hitherto,  there- 
fore, been  principally  directed  to  the  heart  of  cold-blooded  animals, 
e.g.,  the  frog,  tortoise,  and  snake,  which  will  continue  to  beat 
under  favourable  conditions  for  many  hours  after  removal  from  the 
body.  Of  these  animals,  the  frog  is  the  one  mostly  employed, 
and,  indeed,  until  recently,  it  was  from  the  study  of  the  frog's 
heart  that  the  chief  part  of  our  information  was  obtained.  If 
removed  from  the  body  entire,  the  frog's  heart  will  continue  to 
beat  for  many  hours  and  even  days,  and  the  beat  has  no  apparent 
difference  from  the  beat  of  the  heart  before  removal  from  the 
body ;  it  will  take  place  without  the  presence  of  blood  or  other 
fluid  within  its  chambers.  If  the  beats  have  become  infrequent, 
an  additional  beat  may  be  induced  by  stimulating  the  heart 
by  means  of  a  blunt  needle ;  but  the  time  before  the  stimulus 
applied  produces  its  result  (the  latent  period)  is  very  prolonged, 
and  as  in  this  way  the  cardiac  beat  is  like  the  contraction  of 
unstriped  muscle,  the  method  has  been  likened  to  a  peristaltic 
c<  ntraction. 


chap,  v.]  I.\'Fl.ri:.M  i:    OF    NERVOUS    SYSTEM.  155 

There  is  much  uncertainty  about  the  nervous  mechanism  of  the 
beat  of  the  frog's  heart,  but  what  has  just  been  said  shows,  al  any 
rate,  two  things;  firstly,  that  as  the  heart  will  beat  when  removed 
from  the  body  in  a  way  differing  not  at  all  from  the  normal, 
it  must  contain  within  itself  the  mechanism  of  rhythmical  con 
traction  ;  and  secondly,  that  as  it  can  beat  without  the  presence 
of  fluid  within  its  chambers,  the  movement  cannot  depend  merely 
on  reflex  excitation  by  the  entrance  of  blood.  The  nervous  appa- 
ratus existing  in  the  heart  itself  consists  of  collections  of  microscopic 
ganglia,  and  of  nerve-fibres  proceeding  from  them.     These  ganglia 


Yet 


Fig.  io6.—TT(nrt  of  froff.  (Burdon-Sanderson  after  Fritsche.]  Front  view  to  the  left, 
back  new  to  the  right.  A  A.  Aorta1.  V.  cs.  Vente  cav«?  superiores.  At  s,  left 
auricle.  At  d,  right  auricle.  Ven.,  ventricle.  B.  nr.  Bulb  us  arteriosus.  S.  v.,  Sinus 
venosus.  V.  c.  t'.,  Vena  cava  inferior.  J\  h.,  Venie  hepatica.'.  V.  p.,  Vente  pul- 
inonales. 

are  demonstrable  as  being  collected  chiefly  into  three  groups ;  one 
is  in  the  wall  of  the  sinus  venosus  (Remak's)  ;  a  second,  near  the 
junction  between  the  auricle  and  ventricle  (Bidder's)  ;  and  the 
third  in  the  septum  between  the  auricles. 

Some  very  important  experiments  seem  to  identify  the  rhyth- 
mical contractions  of  the  frog's  heart  with  these  ganglia.  If  the 
heart  be  removed  entire  from  the  body,  the  sequence  of  the  con- 
traction of  its  several  beats  will  take  place  with  rhythmical 
regularity,  viz.,  of  the  sinus  venosus,  the  auricles,  the  ventricle, 
and  bulbus  arteriosus,  in  order.  If  the  heart  be  removed  at 
the  junction  of  the  sinus  and  auricle,  the  former  will  continue 
to  beat,  but  the  removed  portion  will  for  a  short  variable  time  stop 
beating,  and  then  resume  its  beats,  but  with  a  rhythm  different 
to  that  of  the  sinus  :  and,  further,  if  the  ventricle  be  removed, 
it  will  take  a  still  longer  time  before  recommencing  its  pulsation 
after  its  removal  than  the  larger  portion  consisting  of  the  auri- 
cles and  ventricle,  and  its  rhythm  is  different  from  that  of  the 
unremoved  portion,  and  not  so  regular,  nor  will  it  continue  to 


156  CIRCULATION    OF    THE    BLOOD.  [chap.  v. 

pulsate  so  long  :  during  the  period  of  stoppage  a  contraction  will 
occur  if  the  ventricle  be  mechanically  or  otherwise  stimulated 
If  the  lower  two-thirds  or  apex  of  the  ventricle  be  removed,  the 
remainder  of  the  heart  will  go  on  beating  regularly  in  the  body,  but 
this  part  will  remain  motionless,  and  will  not  beat  spontaneously, 
although  it  will  respond  to  Btimuli.  If  the  heart  be  divided 
lengthwise,  its  parts  will  continue  to  pulsate  rhythmically,  and 
the  auricles  may  be  cut  up  into  pieces,  and  the  pieces  will  con- 
tinue their  movements  of  contraction.  It  will  be  thus  seen  that 
the  rhythmical  movements  appear  to  be  more  marked  in  the 
parts  supplied  by  the  ganglia,  and  that  the  apical  portion  of  the 
ventricle,  in  which  the  ganglia  are  not  found,  does  not  possess  the 
power  of  automatic  movement.  Although  the  theory  that  the 
pulsations  of  the  rest  of  the  heart  are  dependent  upon  that  of 
the  sinus,  and  to  stimuli  proceeding  from  it,  when  connection  is. 
maintained,  and  only  to  reflex  stimuli  when  removal  has  taken 
place,  cannot  be  absolutely  upheld,  yet  it  is  evident  that  the 
power  of  spontaneous  contraction  is  strongest  in  the  sinus,  less 
strong  in  the  auricles,  and  less  so  still  in  the  ventricle,  and 
that,  therefore,  the  sinus  ganglia  are  probably  important  in  ex- 
citing the  rhythmical  contraction  of  the  whole  heart.  This  is 
expressed  in  the  following  way  : — "  The  power  of  independent 
rhythmical  contraction  decreases  regularly  as  we  pass  from  the 
sinus  to  the  ventricles,"  and  "  The  rhythmical  power  of  each  seg- 
ment of  the  heart  varies  inversely  as  its  distance  from  the  sinus/" 
(Gaskell.) 

It  has  been  recently  shown  that,  under  appropriate  stimuli,  even  the 
extreme  apex  of  the  ventricle  in  the  tortoise  may  take  on  rhythmical  con- 
tractions, or  in  other  words  may  be  "  taught  to  beat ''  rhvthmicallv. 
(Gaskell.) 

Inhibition  of  the  Heart's  Action. — Although,  under  ordinary 
conditions,  the  apparatus  of  ganglia  and  nerve-fibres  in  the  sub- 
stance of  the  heart  forms  the  medium  through  which  its  action  is 
excited  and  rhythmically  maintained,  yet  they,  and,  through  them, 
the  heart's  contractions,  are  regulated  by  nerves  which  pass  to 
them  from  the  higher  nerve-centres.  These  nerves  are  branches 
from  the  pneumogastric  or  vagus  and  the  sympathetic. 

The  influence  of  the  vagi  nerves  over  the  heart-beat  may  be 
shown  by  stimulating  one  (especially  the  right)  or  both   of  the 


chap,  v.]  [NHIBITION    OF    THE    HEART.  I  ;; 

nerves  when  a  record  i>  \»/\wj:  taken  of  the 
heart     If  a  single  induction  shock  be  Bent  into  th<  .  the 

heart,  after  a  short  interval,  <■  -  ~  beating,  but  after  the  bud- 
od  of  several  beats  resumes  its  action.  As  already  mentioned, 
the  effect  of  the  stimulus  is  not  immediately  .seen,  and  one  beat 
may  occur  before  the  heart  stops  after  the  application  of  the 
electric-current.  The  stoppage  of  the  heart  may  occur  apparently 
in  one  of  two  ways,  either  by  diminution  of  the  strength  of  the 
systole  or  by  increasing  the  length  of  the  diastole.  The  stoppage 
of  the  heart  may  be  brought  about  by  the  application  of  the 
electrodes  to  any  part  of  the  vagus,  but  most  effectually  if  they 
are  applied  near  the  position  of  Remak's  ganglia.  It  is  supposed 
that  the  fibres  of  the  vagi,  therefore,  terminate  there  in  inhibitory 
ganglia  in  the  heart-walls,  and  that  the  inhibition  of  the  heart's 
beats,  by  means  of  the  vagus,  is  not  a  simple  action,  but  that  it  is 
produced  by  stimulating  centres  in  the  heart  itself.  These 
inhibitory  centres  are  paralyze!  by  atropin,  and  then  no  amount 
of  stimulation  of  the  vagus,  or  of  the  heart  itself,  will  produce  any 
effect  upon  the  cardiac  beats.  Urari  in  large  doses  paralyzes  the 
vagus  fibres,  but  in  this  case,  as  the  inhibitory  action  can  be  pro- 
duced by  direct  stimulation  of  the  heart,  it  is  inferred  that  this 
drug  does  not  paralyze  the  ganglia  themselves.  Muscarin  and 
pilocarpin  appear  to  produce  effects  similar  to  those  obtained  by 
stimulating  the  vagus  fibres. 

If  a  ligature  be  tightly  tied  round  the  heart  over  the  situation 
of  the  ganglia  between  the  sinus  and  the  auricles,  the  heart  stops 
beating.  This  experiment  (Stannius")  would  seem  to  stimulate  the 
inhibitory  ganglia,  but  for  the  remarkable  fact  that  atropin  does 
not  interfere  with  its  success.  If  the  part  (the  ventricle)  below 
the  ligature  be  cut  off,  it  will  begin  and  continue  to  beat  rhyth- 
mically :  this  may  be  explained  by  supposing  that  the  stimulus 
•tion  induces  pulsation  in  the  part  which  is  removed  from  the 
influence  of  the  inhibitory  ganglia. 

So  far,  the  effect  of  the  terminal  apparatus  of  the  vagi  lias 
been  considered;  there  is.  however,  reason  for  believing  that  the 
vagi  nerves  are  simply  the  media  of  an  inhibito  -     lining 

influence  over  the  action  of  the  heart,  which  is  conveyed  thr     _ 
them  from   a   centre   in  the  medulla   oblongata   which  is  always 
in  operation,  and,  because  of  its  restraining  the  heart's  act: 


158  CIRCULATION    OF    THE    BLOOD.  [chap.  v. 

called  the  cardio-inhibitory  centre.  For,  on  dividing  these  nerves, 
the  pulsations  of  the  heart  are  increased  in  frequency,  an  effect 
opposite  to  that  produced  by  stimulation  of  their  divided  (peri- 
pheral) ends.  The  restraining  influence  of  the  centre  in  the 
medulla  may  be  increased  reflexly,  producing  slowing  or  stoppage 
of  the  heart,  through  influence  passing  from  it  down  the  vagi. 
As  an  example  of  the  latter,  the  well-known  effect  on  the  heart 
of  a  violent  blow  on  the  epigastrium  may  be  referred  to.  The 
stoppage  of  the  heart's  action  is  due  to  the  conveyance  of  the 
stimulus  by  fibres  of  the  sympathetic  to  the  medulla  oblongata, 
and  its  subsequent  reflection  through  the  vagi  to  the  inhibitory 
ganglia  of  the  heart.  It  is  also  believed  that  the  power  of  the 
medullary  inhibitory  centre  may  be  reflexly  lessened,  producing 
accelerated  action  of  the  heart. 

Acceleration  of  Heart's  Action.— Through  certain  fibres  of 
the  sympathetic,  the  heart  receives  an  accelerating  influence  from  the 
medulla  oblongata.  These  accelerating  nerve-fibres,  issuing  from 
the  spinal  cord  in  the  neck,  reach  the  inferior  ceiwical  ganglion, 
and  pass  thence  to  the  cardiac  plexus,  and  so  to  the  heart. 
Their  function  is  shown  in  the  quickened  pulsation  which  follows 
stimulation  of  the  spinal  cord,  when  the  latter  has  been  cut  off 
from  all  connection  with  the  heart,  excepting  that  which  is  formed 
by  the  accelerating  filaments  from  the  inferior  cervical  ganglion. 
Unlike  the  inhibitory  fibres  of  the  pneumogastric,  the  accelerating 
fibres  are  not  continuously  in  action. 

The  accelerator  nerves  must  not,  however,  be  considered  as 
direct  antagonists  of  the  vagus ;  for  if  at  the  moment  of  their 
maximum  stimulation,  the  vagus  be  stimulated  with  minimum 
currents,  inhibition  is  produced  with  the  same  readiness  as  if  these 
were  not  acting. 

The  connection  of  the  heart  with  other  organs  by  means  of  the 
nervous  system,  and  the  influences  to  which  it  is  subject  through 
them,  are  shown  in  a  striking  manner  by  the  phenomena  of 
disease.  The  influence  of  mental  shock  in  arresting  or  modifying 
the  action  of  the  heart,  the  slow  pulsation  which  accompanies  com- 
pression of  the  brain,  the  irregularities  and  palpitations  caused  by 
dyspepsia  or  hysteria,  are  good  evidence  of  the  connection  of  the 
heart  with  other  organs  through  the  nervous  system. 

The  action  of  the  heart  is  no  doubt  also  very  materially  affected 


chap,  v.]  THE    AETERIES.  159 

by  the  nutrition  oi  its  walls  l>y  a  sufficient  supply  of  healthy 
blood  sent  to  them,  and  it  is  not  unlikely  that  the  apparently 
contradictory  effect  of  poisons  may  be  explained  by  supposing  that 
the  influence  of  some  of  them  is  either  partially  or  entirely 
directed  t<>  the  muscular  tissue  itself,  and  not  to  the  nervoue 
apparatus  alone.  As  will  be  explained  presently,  the  heart  exerci 
a  considerable  influence  upon  the  condition  of  the  pressure  of 
blood  within  the  arteries,  but  in  its  turn  the  blood-pressure  within 
the  arteries  reacts  upon  the  heart,  and  lias  a  distinct  effect  upon 
its  contractions,  increasing  by  its  increase,  and  rice  versd,  the  force  oi 
the  cardiac  beat,  although  the  frequency  is  diminished  as  the  blood- 
pressure  rises.  The  quantity  (and  quality?)  of  the  blood  contained 
in  each  chamber,  too,  has  an  influence  upon  its  systole,  and  within 
normal  limits  the  larger  the  quantity  the  stronger  the  contraction. 
Rapidity  of  systole  does  not  of  necessity  indicate  strength,  as  two 
weak  contractions  often  do  no  more  work  than  one  strong  and 
prolonged.  In  order  that  the  heart  may  do  its  maximum  work, 
it  must  be  allowed  free  space  to  act;  for  if  obstructed  in  its 
action  by  mechanical  outside  pressure,  as  by  an  excess  of  fluid 
within  the  pericardium,  such  as  is  produced  by  inflammation,  or  by 
an  overloaded  stomach,  or  what  not,  the  pulsations  become 
irregular  and  feeble. 

The   Arteries. 

Distribution. — The  arterial  system  begins  at  the  left  ventricle 
in  a  single  large  trunk,  the  aorta,  which  almost  immediately 
after  its  origin  gives  off"  in  its  course  in  the  thorax  three  large 
branches  for  the  supply  of  the  head,  neck,  and  upper  extremities  ; 
it  then  traverses  the  thorax  and  abdomen,  giving  off  branches, 
some  large  and  some  small,  for  the  supply  of  the  various  organs 
and  tissues  it  passes  on  its  way.  In  the  abdomen  it  divides  into 
two  chief  branches,  for  the  supply  of  the  lower  extremities.  The 
arterial  branches  wherever  given  off  divide  and  subdivide,  until  the 
calibre  of  each  subdivision  becomes  very  minute,  and  these  minute 
vessels  pass  into  capillaries.  Arteries  are,  as  a  rule,  placed  in 
situations  protected  from  pressure  and  other  dangers,  and  are,  with 
few  exceptions,  straight  in  their  course,  and  frequently  com- 
municate with  other  arteries  (anastomose  or  inosculate).  The 
branches  are  usually  given  off  at  an  acute  angle,  and  the  area  of 


i6o 


CIRCULATION    OF    THE    BLOOD. 


[CHAI*.   V. 


the  branches  of  an  artery  generally  exceeds  that  of  the  parent 
trunk ;  and  as  the  distance  from  the  origin  is  increased,  the  area  of 
the  combined  branches  is  increased  also. 

After  death,  arteries  are  usually  found  dilated  (not  collapsed  as 
the  veins  are)  and  empty,  and  it  was  to  this  fact  that'  their  name 
was  given  them,  as  the  ancients  believed  that  they  conveyed  air 
to  the  various  parts  of  the  body.  As  regards  the  arterial  system 
of  the  lungs  (pulmonary  system)  it  begins  at  the  right  ventricle  in 
the  pulmonary  artery,  and  is  distributed  much  as  the  arteries 
belonging  to  the  general  systemic  circulation. 

Structure.— The  walls  of  the  arteries  are  composed  of  three 
principal  coats,  termed  the  external  or  tunica  adventitia,  the  middle 
or  tunica  media,  and  the  internal  coat  or  tunica  intima. 

The  external  coat  or  tunica  adventitia  (figs.  107  and  in,  t.  a.), 
the  strongest  and  toughest  part  of  the 
wall  of  the  artery,  is  formed  of  areolar 
tissue,  with  which  is  mingled  throughout 
a  network  of  elastic  fibres.  At  the  inner 
part  of  this  outer  coat  the  elastic  network 
forms  in  most  arteries  so  distinct  a  layer 
as  to  be  sometimes  called  the  external 
elastic  coat  (fig.  123,  e.  e.). 

The  middle  coat  (fig.  107,  m)  is  composed 
of  both  muscular  and  elastic  fibres,  with  a 
certain  proportion  of  areolar  tissue.  In 
the  larger  arteries  (fig.  no)  its  thickness 
is  comparatively  as  well  as  absolutely 
much  greater  than  in  the  small,  consti- 
tuting, as  it  does,  the'  greater  part  of  the 
arterial  wall. 

The  muscular  fibres,  which  are  of  the 
unstriped  variety  (fig.  109)  are  arranged 
for  the  most  part  transversely  to  the  long- 
axis  of  the  artery  (fig.  107,  m) ;  while  the 
elastic  element,  taking  also  a  transverse  direction,  is  disposed  in 
the  form  of  closely  interwoven  and  branching  fibres,  which  inter- 
sect in  all  parts  the  layers  of  muscular  fibre.  In  arteries  of 
various  size  there  is  a  difference  in  the  proportion  of  the  muscular 
and  elastic  element,  elastic  tissue  preponderating  in  the  largest 


Fig.  107. — Minute  arte  review- 
ed in  longitudinal  section. 
e.  Nucleated  endothelial 
membrane,  with  faint 
nuclei  in  lumen,  looked  at 
from  above,  i.  Thin  elas- 
tic tunica  intima.  m.  Mus- 
cular coat  or  tunica  media. 
a.  Tunica  adventitia. 
(Klein  and  Noble  Smith.) 
X  250. 


<   II  A  I 


STRUCTURE    OF    ARTERIES. 


161 


arteries,  while  this  condition  is  reversed  in  those  of  medium  and 
small  size. 

The  internal  coat  is  formed  bj  layers  of  elastic  tissue,  consisting 
in  part  of  coarse  longitudinal  branching  fibres,  and  in  part  of  a 


Hi 


108. — Portion  of  j  from  the  femoral  artery,     x  :m. 

a,  b,  r.  PerforatioiLS.     (Henle.) 


very  thin  and  brittle  membrane  which  possesses  little  elasticity, 
and  is  thrown  into  folds  or  wrinkles  when  the  artery  contracts. 
This  latter  membrane,  the  striated  or  fenestrated  coat  of  Htnle 
(fig.  1 08),  is  peculiar  in  its  tendency  to   curl  up,  when  peeled  off 

/I,  J 


Fig.  109. — Muscular  fbre-edls  from  human  aruries,  magnified  350  diameters.     (Kulliker.) 
n.  Nucleus,     b.  A  fibre-cell  treated  with  acetic  acid. 

from  the  artery,  and  in  the  perforated  and  streaked  appearance 
which  it  presents  under  the  microscope.  Its  inner  surface  is  lined 
with  a  delicate  layer  of  endothelium,  composed  of  elongated  cells 

M 


1 62 


CIRCULATION    OF    TIIE    BLOOD. 


[chap.  v. 


(fig.  ii2,  a),  which  make  it  smooth  and  polished,  and  furnish  a 
nearly  impermeable  surface,  along  which  the  blood  may  flow  with 
the  smallest  possible  amount  of  resistance  from  friction. 

Immediately  external  to  the  endothelial  lining  of  the  artery  is 
fine   connective    tissue,  sub-endothelial   layer,   with  branched  cor- 


&s 


536 


h^r-^'S^riS 


1  &&-. 


Fig.  no. Transverse,  section  of  aorta  through  internal  and  about  Turff  th?   middle   coat.     a. 

Linm0*  endothelium  with  the  nuclei  of  the  cells  only  shown,  h.  Subepithelial 
layer  °of  connective  tissue,  c,  d.  Elastic  tunica  intima  proper,  with  fibrils  running 
circularly  or  longitudinally.  «,  /.  Middle  coat,  consisting  of  elastic  fibres  arranged 
longitudinally,  with  muscle-fibres  cut  obliquely,  or  longitudinally.     (Klein.) 

puscles.  Thus  the  internal  coat  consists  of  three  parts,  (a)  an 
endothelial  lining,  (6)  the  sub-endothelial  layer,  and  (c)  elastic 
layers. 

Vasa  Vasorum. — The  walls  of  the  arteries,  with  the  possible 
exception  of  the  endothelial  lining  and  the  layers  of  the  internal 
coat  immediately  outside  it,  are  not  nourished  by  the  blood  which 
they  convey,  but  are,  like  other  parts  of  the  body,  supplied  with 
little  arteries,  ending  in  capillaries  and  veins,  which,  branching 
throughout  the  external  coat,  extend  for  some  distance  into  the 


I  BAP.   v.  ] 


STRUCTURE    OF    ARTERIES. 


163 


middle,  l>ut  do  not  reach  the  internal  ooat     These  nutrient  vet 
died  Ml  <m. 

Lymphatics  of  Arteries  and  Veins.      Lymphatic  spaces  are 
nt  in  the  coats  of  both  arteries  and  veins;  but  in  the  tunica 


Fig.  in. —  Tramsvene  section  of  small  artery  from  soft  palate,  e,  endothelial  linin?,  the 
nuclei  of  the  cells  are  shown ;  i,  elastic  tissue  of  the  intima,  which  is  a  good  deal 
folded  ;  c.  m.  circular  muscular  coat,  showiug  nuclei  of  the  muscle  cells  ;  /.  a.  tunica 
advent  it  ia.         x  300.     (Sehofield.) 

adventitia  or  external   coat   of  large  vessels  they  form  a  distinct 
plexus  of  more  or  less  tubular  vessels.      In  smaller  vessels  they 


Fig.  112. — Tko  blood-vessels  from  a  frog's  mesentery,  injected  with  nitrate  of  silver,  shoving 
the  outlines  of  the  endothelial  cells,  a.  Artery.  The  endothelial  cells  are  long  and 
narrow;  the  transverse  markings  indicate  the  muscular  coat.  t.  a.  Tunica  adven- 
titia. v.  Feat,  Showing  the  shorter  and  wider  endothelial  cells  with  which  it  is  lined, 
c,  c.  Two  capillaries  entering  the  vein.     (Schofield.) 

ap^ar  us  sinous  -paces  lined  by  endothelium.  Sometimes,  as  in 
the  arteries  of  the  omentum,  mesentery,  and  membranes  of  the 
brain,  in  the  pulmonary,  hepatic,  and  splenic  arteries,  the  spaces 

M    2 


if>4 


CIRCULATION    OF    THE    BLOOD. 


[chap.  v. 


are  continuous  with  vessels  which  distinctly  ensheath  them — 
perivascular  lymphatic  sheatlis  (fig.  121).  Lymph  channels  are  said 
to  be  present  also  in  the  tunica  media. 


Fig.  113. — Blood-vessels  from  mesocolon  of  rabbit,  a.  Artery,  with  two  branches,  showing' 
tr.n.  nuclei  of  transverse  muscular  fibres;  1.  n.  nuclei  of  endothelial  lining;  t.  a. 
tunica  adventitia.  v.  Venn.  Here  the  transverse  nuclei  are  more  oval  than  those  of 
the  artery.  The  vein  receives  a  small  branch  at  the  lower  end  of  the  drawing  ;  it  is 
distinguished  from  the  artery  among  other  things  by  its  straighter  course  and  larger 
calibre,    c.  Capillary,  showing  nuclei  of  endothelial 'cells,     x  300.     (Schofield.) 

Nervi  Vasorum. — Most  of  the  arteries  are  surrounded  by  a 
plexus  of  sympathetic  nerves,  which  twine  around  the  vessel  very 
much  like  ivy  round  a  tree  :  and  ganglia  are  found  at  frequent 
intervals.  The  smallest  arteries  and  capillaries  are  also  surrounded 
by  a  very  delicate  network  of  similar  nerve-fibres,  many  of 
which  appear  to  end  in  the  nuclei  of  the  transverse  muscular  fibres 
(fig.  122).  It  is  through  these  plexuses  that  the  calibre  of  the 
vessels  is  regulated  by  the  nervous  system  (p.  190). 

The    Capillaries. 

Distribution. — In  all  vascular  textures,  except  some  parts  of 
the  corpora  cavernosa  of  the  penis,  and  of  the  uterine  placenta, 


OHAP.  v.] 


CAI'l  l.l.A  III  KS. 


t6s 


;ui(l  of  the  Bpleen,  tin-  transmission  of  the  blood  from  the  minute 
branohes  of  the  arteries  to  the  minute  veins  is  effected  through  a 
network    of    microscopic    vessels,    called 
capillaries.      These   may  be  seen    in  all 
minutely     injected     preparations  ;     and 

during  life,  in  any  transparent  vascular 
parts,  such  as  the  web  <>f  the  frog's  foot, 
the  tail  or  external  branchiae  of  the  tad 

pole,  or  the  wing  of  the  hat. 

The  branches  of  the  minute  arteries 
form  repeated  anastomoses  with  each 
other,  and  give  oft'  the  capillaries  which, 
by  their  anastomoses,  compose  a  conti- 
nuous and  uniform  network,  from  which 
the  venous  radicles  take  their  rise  (fig. 
114).  The  point  at  which  the  arteries 
terminate  and  the  minute  veins  com- 
mence, cannot  be  exactly  defined,  for  the 
transition  is  gradual  ;  but  the  capillary 
network  has,  nevertheless, this  peculiarity,    K&-   iw—Biood-vt 

1  "  '        intestinal 

that  the  small  vessels  which  compose  it 

maintain  the  same  diameter  throughout : 

they  do  not  diminish  in  diameter  in  one 

direction,  like  arteries  and  veins  ;  and  the  meshes  of  the  network 

that  they  compose  are  more  uniform  in  shape  and  size  than  those 

formed  by  the  anastomoses  of  the  minute  arteries  and  veins. 

Structure. — This  is  much  more  simple  than  that  of  the  arteries 
or  veins.  Their  walls  are  composed  of  a  single  layer  of  elongated 
or  radiate,  flattened  and  nucleated  cells,  so  joined  and  dovetailed 
together  as  to  form  a  continuous  transparent  membrane  (fig.  115). 
Outside  these  cells,  in  the  larger  capillaries,  there  is  a  structureless, 
or  very  finely  fibrillatcd  membrane,  on  the  inner  surface  of  which 
they  arc  laid  down. 

In  some  cases  this  external  membrane  is  nucleated,  and  may 
then  be  regarded  as  a  miniature  representative  of  the  tunica 
adventitia  of  arteries. 

Here  and  there,  at  the  junction  of  two  or  more  of  the  delicate 
endothelial  cells  which  compose  the  capillary  wall,  pxeudo-stomata 
may   be  seen   resembling   those    in    serous    membranes  (p.   367) 


villus,  representing 
the  arrangement  of  capil- 
laries between  the  ultimate 
venous  and  arterial  branches ; 
a,  a,  the  arteries;  b,  the  vein. 


1 66 


CIRCULATION    OF    THE    BLOOD. 


[chap.  v. 


The  endothelial  cells  are  often  continuous  at  various  points  with 
processes  of  adjacent  connective-tissue  corpuscles. 


Fig.  115. — Capillary  blood-vessels  from  the  omentum  of  rabbit,  showing  the  nucleated  endo- 
thelial membrane  of  which  they  are  composed.      (Klein  and  Xoble  Smith.) 


Capillaries  are  surrounded  by  a  delicate  nerve-plexus  resembling, 
in  miniature,  that  of  the  larger  blood-vessels. 

The  diameter  of  the  capillary 
vessels  varies  somewhat  in  the  dif- 
ferent textures  of  the  body,  the  most 
common  size  being  about  3-^ooth  of 
an  inch.  Among  the  smallest  may 
be  mentioned  those  of  the  brain,  and 
of  the  follicles  of  the  mucous  mem- 
brane of  the  intestines ;  among  the 
largest,  those  of  the  skin,  and  espe- 
cially those  of  the  medulla  of  bones. 
The  size  of  capillaries  varies  neces- 
sarily in  different  animals  in  relation 
to  the  size  of  their  blood  corpuscles  : 
thus,  in  the  Proteus,  the  capillary 
circulation  can  just  be  discerned 
with  the  naked  eye. 

The  form  of  the  capillary  network 
presents  considerable  variety  in  the  different  textures  of  the  body : 
the  varieties  consisting  principally  of  modifications  of  two  chief 
kinds  of  mesh,  the  rounded  and  the  elongated.     That  kind  of 


Fig.  116. — Network  of  capillary  vessels 
of  the  air-cells  of  the  horse's  limy 
magnified,  a,  a,  capillaries  pro- 
ceeding from  b,  b,  terminal 
branches  of  the  pulmonary 
artery.     (Frey.) 


t  II  IF.   v.  I 


CAPILLARIES. 


167 


which  the  meshes  or  interspaces  have  a  roundish  form  is  the  most 
common,  and  prevails  in  those  parts  in  which  the  capillary  net- 
work is  most  dense,  such  as  the  lungs  (fig.  116),  most  glands,  and 
mucous  membranes,  and  the  cutis.  The  meshes  of  this  kind  of 
network  are  not  quite  circular  but  more  or  less  angular,  some- 
times presenting  a  nearly  regular  quadrangular  or  polygonal  form, 
but  being  more  frequently  irregular.  The  capillary  network  with 
elongated  meshes  (fig.  117)  is  observed  in  parts  in  which  the 
vessels  are  arranged  among  bundles  of  tine  tubes  or  fibres,  as  in 
muscles  and  nerves.  In  such  parts,  the 
meshes  usually  have  the  form  of  a  parallelo- 
gram, the  short  sides  of  which  may  be  from 
three  to  eight  or  ten  times  less  than  the  long 
ones;  the  long  sides  always  corresponding  to 
the  axis  of  the  fibre  or  tube,  by  which  it  is 
placed.  The  appearance  of  both  the  rounded 
and  elongated  meshes  is  much  varied  accord- 
ing as  the  vessels  composing  them  have  a 
straight  or  tortuous  form.  Sometimes  the 
capillaries  have  a  looped  arrangement,  a  single 
capillary  projecting  from  the  common  network 
into  some  prominent  organ,  and  returning 
after  forming  one  or  more  loops,  as  in  the 
papilla?  of  the  tongue  and  skin. 

The  number  of  the  capillaries  and  the  size 
of  the  meshes  in  different  parts  determine  in 
general  the  degree  of  vascularity  of  those 
parts.  The  parts  in  which  the  network  of  capillaries  is  closest, 
that  is,  in  which  the  meshes  or  interspaces  are  the  smallest, 
are  the  lungs  and  the  choroid  membrane  of  the  eye.  In  the  iris 
and  ciliary  body,  the  interspaces  are  somewhat  wider,  yet  very 
small.  In  the  human  liver  the  interspaces  are  of  the  same  size, 
or  even  smaller  than  the  capillary  vessels  themselves.  In  the 
human  lung  they  are  smaller  than  the  vessels  ;  in  the  human 
kidney,  and  in  the  kidney  of  the  dog,  the  diameter  of  the  injected 
capillaries,  compared  with  that  of  the  interspaces,  is  in  the  pro- 
portion of  one  to  four,  or  of  one  to  three.  The  brain  receives  a 
very  large  quantity  of  blood ;  but  the  capillaries  in  which  the 
blood  is  distributed  through  its  substance  are  very  minute,  and 


Fig.  117. — Injected  capil- 
lary   vessels  of  musrl, 

seen  with  a  low  mag- 
nifying power. 

(Sharpey.) 


1 63  CIRCULATION    OF    THE    BLOOD.  [chap.  v. 

Less  numerous  than  in  some  other  parts.  Their  diameter,  accord- 
ing to  E.  H.  Weber,  compared  with  the  long  diameter  of  the 
meshes,  being  in  the  proportion  of  one  to  eight  or  ten  :  compared 
with  the  transverse  diameter,  in  the  proportion  of  one  to  four  or 
six.  In  the  mucous  membranes — for  example  in  the  conjunctiva 
and  in  the  cutis  vera,  the  capillary  vessels  are  much  larger  than 
in  the  brain,  and  the  interspaces  narrower,  —namely,  not  more 
than  three  or  four  times  wider  than  the  vessels.  In  the  periosteum 
the  meshes  are  much  larger.  In  the  external  coat  of  arteries, 
the  width  of  the  meshes  is  ten  times  that  of  the  vessels  (Henle). 

It  may  be  held  as  a  general  rule,  that  the  more  active  the 
functions  of  an  organ  are,  the  more  vascular  it  is.  Hence  the 
narrowness  of  the  interspaces  in  all  glandular  organs,  in  mucous 
membranes,  and  in  growing  parts ;  their  much  greater  width  in 
bones,  ligaments,  and  other  very  tough  and  comparatively  inactive 
tissues;  and  the  usually  complete  absence  of  vessels  in  cartilage,  and 
such  parts  as  those  in  which,  probably,  very  little  vital  change 
occurs  after  they  are  once  formed. 

The   Veins. 

Distribution. — The  venous  system  begins  in  small  vessels  which 
are  slightly  larger  than  the  capillaries  from  which  they  spring. 
These  vessels  are  gathered  up  into  larger  and  larger  trunks  until 
they  terminate  (as  regards  the  systemic  circulation)  in  the  two 
vena?  cayse  and  the  coronary  veins,  which  enter  the  right  auricle, 
and  (as  regards  the  pulmonary  circulation)  in  four  pulmonary 
A-eins,  which  enter  the  left  auricle.  The  capacity  of  the  veins 
diminishes  as  they  approach  the  heart  :  but,  as  a  rule,  the  capacity 
of  the  veins  exceeds  by  several  times  (twice  or  three  times)  that 
of  their  corresponding  arteries.  The  pulmonary  veins,  however, 
are  an  exception  to  this  rule,  as  they  do  not  exceed  in  capacity  the 
pulmonary  arteries.  The  veins  are  found  alter  death  as  a  rule  to 
be  more  or  less  collapsed,  and  often  to  contain  blood.  The  veins 
are  usually  distributed  in  a  superficial  and  a  deep  set  which 
communicate  frequently  in  their  course. 

Structure. — In  structure  the  coats  of  veins  bear  a  general  re- 
semblance to  those  of  arteries  (fig.  nS).  Tims,  they  possess  an 
autert  middle,  and  internal  coat.     The  outer  coat  is  constructed  of 


THE    VEINS 


I  69 


arclar  tissue  like  that  of  the  .  but   ifl  thicker.     In  some 

veins  it  contains  muscular  fibre-cells,  which  are  arranged  longitu- 
dinally. 

The   i"  soat    is   considerably   thinner  than   that   of    the 

arteries  ;  and,  although    it   contains  circular  unstriped   musculai 


■^mmm§ 


€.1 


Fiu  118—  Tt  •  '  arten  a,, J  vein  of  the  mucoid  membrane  01  .< 

cnuo^s  epiglottis :  the  contrast  between  the  thick-willed  artery  and  the  thin-walled 
vein  is  well  -huwn.  A.  Arterr,  the  letter  is  placed  in  the  lumen  of  the  vessel,  e.  hu- 
doth-lial  cells  with  nuclei  clearly  visible:  these  cells  appear  very  thick  from  th* 
contracted  state  of  the  vessel.  Outside  it  a  double  wavy  line  marks  the  elastic  tunic  1 
intim  1  m  Tunica  media  forming  the  chief  part  of  arterial  wall  and  consisting  01 
un«triped  musculai:  fibres  circularly  arranged  :  their  nuclei  are  well  seen.  a.  Fart ;  ot 
UV  tunica  ndventitia  .-howine  bundles  of  connective-ti--  -   m  >e- -tion,  with tn- 

orcular  nuclei  of  the  connective-tissue  corpuscles.     This  coat  gradually  merge- 
the  surrounding  connective-ti-ue.     V.  In  the  lumen  of  the  vein.     The  other  letter- 
indicate  the  same  as  in  the  artery.    The  muscular  coat  of  the  vein   m   «  seen  to  De 
mu.-h  thinner  than  that  of  the  artery.  Klein  and  Noble  Smith. 

fibres  or  fibre-cells,  these  are  mingled  with  a  larger  proportion  of 

yellow  elastic  and  white  fibrous  tissue.  In  the  large  veins,  near 
the  heart,  namely  the  vena  cava  and  pulmonary  veins,  the  middle 
coat  is  replaced,  lor  Borne  distance  from  the  heart,  by  circularly 

arranged  striped  muscular   fibres,    continuous   with  those  of  the 

auricles. 

The  rfcoat  of  veins  is  less  brittle  than  the  corresponding 

c«»at  of  an  artery,  but  in  other  resp    rts      a  mblee  it  closely. 


170 


CIRCULATION    OF    THE    BLOOD. 


[chat*,  v. 


Valves. — The  chief  influence  which  the  veins  have  in  the 
circulation,  is  effected  with  the  help  of  the  valves,  which  arc  placed 
in  all  veins  subject  to  local  pressure  from  the  muscles  between 
or  near  which  they  run.  The  general  construction  of  these  valves 
is  similar  to  that  of  the  semilunar  valves  of  the  aorta  and  pul- 
monary artery,  already  described  ;  but  their  free  margins  are 
turned  in  the  opposite  direction,  i.e.,  towards  the  heart,  so  as  to 
stop  any  movement  of  blood  backward  in  the  veins.  They  are 
commonly  placed  in  pairs,  at  various  distances  in  different  veins, 
but  almost  uniformly  in  each  (fig.   119).      In   the  smaller  veins, 


Fig.  119. — Diagram  showing  valves  of  veins,  a,  part  of  a  vein  laid  open  and  spread  out,  with 
two  pairs  of  valves,  b.  longitudinal  section  of  a  vein,  showing  the  apposition  of  the 
edges  of  the  valves  in  their  closed  state,  c,  portion  of  a  distended  vein,  exhibiting  a 
swelling  in  the  situation  of  a  pair  of  valves. 


single  valves  are  often  met  with  ;  and  three  or  four  are  sometimes 
placed  together,  or  near  one  another,  in  the  largest  veins,  such  as 
the  subclavian,  and  at  their  junction  with  the  jugular  veins.  The 
valves  are  semilunar  ;  the  unattached  edge  being  in  some  examples 
concave,  in  others  straight  They  are  composed  of  inextensile 
fibrous  tissue,  and  are  covered  with  endothelium  like  that  lining 
the  veins.  During  the  period  of  their  inaction,  when  the  venous 
blood  is  flowing  in  its  proper  direction,  they  lie  by  the  sides  of  the 
veins ;  but  when  in  action,  they  close  together  like  the  valves  of 
the  arteries,  and  offer  a  complete  barrier  to  any  backward  move- 
ment of  the  blood  (figs.  119  and  120).  Their  situation  in  the 
superficial  veins  of  the  forearm  is  readily  discovered  by  pressing 
along  its  surface,  in  a  direction  opposite  to  the  venous  current, 
i.  e.,   from  the  elbow  towards   the   wrist ;    when  little  swellings 


<  HA)'.    V.] 


VEINS. 


171 


(fig.  119,  c)  appear  in  the  position  of  each  pair  of  valves.     These 
swellings  at  once  disappear  when  the  pressure  is  relaxed. 

Valves  are  not  equally  uumeroue  in  all  veins,  and  in  many  they 
are  absent  altogether.  They  are  most  numerous  in  the  veins  of 
the  extremities,  and  more  so  in  those  of  the  leg  than  the  arm. 
They  are  commonly  absent  in  veins  of  less  than  a  line  in  diameter, 
and.  as  a   general    rule.  There   are   few  or  none    in    those  whieh  are 

not  subject  to  muscular  pressure.     Among  those  veins  which  have 


Fig.  120.— a,  mm  wiik  wfcei  open.    b.  km  unfk  vi:  stream  of  blood  passing  olf 

by  lateral  channel.     (Dalton.) 

no  valves  may  be  mentioned  the  superior  and  inferior  vena  cava, 
the  trnnk  and  branches  of  the  portal  vein,  the  hepatic  and  renal 
veins,  and  the  pulmonary  veins  :  those  in  the  interior  of  the 
cranium  and  vertebral  column,  those  of  the  bones,  and  the  trunk 
and  branches  of  the  umbilical  vein  are  also  destitute  of  valves. 


Circulation  in  the  Arteries. 

Functions  of  the  External  Coat  of  Arteries. — The  ex- 
ternal coat  forms  a  strong  and  tough  investment,  which,  though 
capable  of  extension,  appears  principally  designed  to  strengthen 
the  arteries  and  to  guard  against  their  excessive  distension  by  the 
force  of  the  heart's  action.     It  is  this  coat  which   alone  prevents 


i;2  CIRCULATION    OF    THE    BLOOD.  [chap.  v. 

the  complete  severance  of  an  artery  when  a  ligature  is  tightly 
applied  ;  the  internal  and  middle  coats  being  divided.      In  it,  too, 


i"isr.  121. — Surfat  ■<-  view  of  an  artery  from  the  mesentery  or  a  j''<>:/,  ensheathed  in.  a  periva — 
cular   lymphatic   vessel,     o.   The  artery,  with  its    circular   muscular    coat    (media' 
indicated  by  broad  transverse  markings,  with  an  indication  of  the  adventitia  outside 
/.  Lymphatic  vessel ;  its  wall  is  a  simple  endothelial  membrane.     (.Klein  and  Noble 
Smith. 

the  little  vasa  vasorum  (p.  162)  find  a  suitable   tissue  in  which  to 
subdivide  for  the  supply  of  the  arterial  coats. 

Functions  of  the  Elastic  Tissue  in  Arteries. — The  pur- 
pose of  the  elastic  tissue,  which  enters  so  largely  into  the  formation 
of  all  the  coats  of  the  arteries,  is,  (a)  to  guard  the  arteries  from 
the  suddenly  exerted  pressure  to  which  they  are  subjected  at  each 
contraction  of  the  ventricles.  In  every  such  contraction,  the  con- 
tents of  the  ventricles  are  forced  into  the  arteries  more  quickly 
than  they  can  be  discharged  into  and  through  the  capillaries. 
The  blood  therefore,  being,  for  an  instant,  resisted  in  its  onward 
course,  a  part  of  the  force  with  which  it  was  impelled  is  directed 
against  the  sides  of  the  arteries  ;  under  this  force  their  elastic- 
walls  dilate,  stretching  enough  to  receive  the  blood,  and  as  they 
stretch,    becoming    more    tense    and    more   resisting.       Thus,  by 


chap.  v.|  FUNCTIONS    OF    A.KTERIES.  173 

yielding,  they  break  the  shock  of  the  force  Impelling  the 
blood.  On  the  subsidence  of  the  pressure,  when  the  ventricles 
cease  contracting,  the  arteries  are  able,  by  the  same  elasticity,  to 
resume  their  former  calibre  ;  (f>.)  It  equalizes  the  current  of  the 
blood  by  maintaining  pressure  on  it  in  the  arteries  during  the  periods 


Fig.  122. — li'in/ijication  of  nerves  and  termination  in  the  muscular  coat  of  a  small  artery  of 

the  frog1  (Arnold). 

at  which  the  ventricles  are  at  rest  or  dilating.  If  the  arteries  had 
been  rigid  tubes,  the  blood,  instead  of  flowing,  as  it  does,  in  a  con- 
stant stream,  would  have  been  propelled  through  the  arterial  system 
in  a  series  of  jerks  corresponding  to  the  ventricular  contractions, 
with  intervals  of  almost  complete  rest  during  the  inaction  of  the 
ventricles.  But  in  the  actual  condition  of  the  arteries,  the  force 
of  the  successive  contractions  of  the  ventricles  is  expended  partly 
in  the  direct  propulsion  of  the  blood,  and  partly  in  the  dilatation 
of  the  elastic  arteries ;  and  in  the  intervals  between  the  con- 
tractions of  the  ventricles,  the  force  of  the  recoil  is  employed  in 
continuing  the  same  direct  propulsion.  Of  course,  the  pressure 
they  exercise  is  equally  diffused  in  every  direction,  and  the  blood 
tends  to  move  backwards  as  well  as  onwards,  but  all  movement 
backwards  is  prevented  by  the  closure  of  the  semi-lunar  arterial 
valves  (p.  141),  which  takes  place  at  the  very  commencement  of 
the  recoil  of  the  arterial  walls. 


174 


CIRCULATION    OF    TEE    BLOOD. 


[chap.  v. 


By  this  exercise  of  the  elasticity  of  the  arteries,  all  the  force  of 
the  ventricles  is  made  advantageous  to  the  circulation ;  for  that 

part  of  their  force  which  is  ex- 
pended in  dilating  the  arteries, 
is  restored  in  full  when  they 
recoil.  There  is  thus  no  loss  of 
force  ;  but  neither  is  there  any 
gain,  for  the  elastic  walls  of  the 
artery  cannot  originate  any  force 
for  the  propulsion  of  the  blood 
— they  only  restore  that  which 
they  received  from  the  ventri- 
cles. The  force  with  which  the 
arteries  are  dilated  every  time 
the  ventricles  contract,  might 
be  said  to  be  received  by  them 
in  store,  to  be  all  given  out 
again  in  the  next  succeeding 
period  of  dilatation  of  the  ven- 
tricles. It  is  by  this  equalizing 
influence  of  the  successive 
branches  of  every  artery  that,  at 
length,  the  intermittent  accele- 
rations produced  in  the  arterial  current  by  the  action  of  the  heart, 
cease  to  be  observable,  and  the  jetting  stream  is  converted  into 
the  continuous  and  equable  movement  of  the  blood  which  we  see 
in  the  capillaries  and  veins.  In  the  production  of  a  continuous 
stream  of  blood  in  the  smaller  arteries  and  capillaries,  the  resist- 
ance which  is  offered  to  the  blood-stream  in  these  vessels  (p.  197), 
is  a  necessary  agent.  Were  there  no  greater  obstacle  to  the  escape 
of  blood  from  the  larger  arteries  than  exists  to  its  entrance  into 
them  from  the  heart,  the  stream  would  be  intermittent,  notwith- 
standing the  elasticity  of  the  walls  of  the  arteries. 

(c.)  By  means  of  the  elastic  tissue  in  their  walls  (and  of  the 
muscular  tissue  also),  the  arteries  are  enabled  to  dilate  and 
contract  readily  in  correspondence  with  any  temporary  increase 
or  diminution  of  the  total  quantity  of  blood  in  the  body  ;  and 
within  a  certain  range  of  diminution  of  the  quantity,  still  to 
exercise  due  pressure  on  their  contents;  (77.)  The  elastic  tissue 


Fig.  123. —  Transversa  section  through  a  large 
branch  of  the  inferior  mesenteric  artery 
of  a  pig.  e,  endothelial  memhrane  ;  i,  tu- 
nica elastica  interna,  no  subendothelial 
layer  is  seen ;  m,  muscular  tunica  media, 
containing  only  a  few  wavy  elastic 
fibres ;  ee,  tunica  elastica  externa, 
dividing  the  media  from  the  connec- 
tive tissue  adventitia,  «.  (Klein  and 
Noble  Smith.)        x  350. 


chap,  v.]  FUNCTIONS    OP    AKTK1UKS.  ^5 

assists  in  restoring  the  norma]  state  after  diminution  of  its  calibre, 
whether  this  lias  been  caused  l>y  a  contraction  of  the  muscular 
coat,  or  the  temporary  application  of  a  compressing  force  from 
without.      This  action   is   well  shown   in   arteries  which,  having 

OOntracted  by  means  of  their  muscular  element,  after  death,  regain 

their  average  patency  on   the  cessation  of  post-mortem  rigidity 

(p.  177).  (('■)  By  means  of  their  elastic  coat  the  arteries  are 
enabled  to  adapt  themselves  to  the  different  movements  of  the 
several  parts  of  the  body. 

Tension  of  Arteries. — The  natural  state  of  all  arteries,  in  regard 
at  least  to  their  length,  is  one  of  tension — they  are  always  more 
or  less  stretched,  and  ever  ready  to  recoil  by  virtue  of  their 
elasticity,  whenever  the  opposing  force  is  removed.  The  extent 
to  which  the  divided  extremities  of  arteries  retract  is  a  measure  of 
this  tension,  not  of  their  elasticity.      (Savory.) 

Functions  of  the  Muscular  Coat. — The  most  important 
office  of  the  muscular  coat  is,  (l)  that  of  regulating  the  quantity  of" 
blood  to  be  received  by  each  part  or  organ,  and  of  adjusting  it  to 
the  requirements  of  each,  according  to  various  circumstances,  but, 
chiefly,  according  to  the  activity  with  which  the  functions  of  each 
are  at  different  times  performed.  The  amount  of  work  done 
by  each  organ  of  the  body  varies  at  different  times,  and  the 
variations  often  quickly  succeed  each  other,  so  that,  as  in  the 
brain,  for  example,  during  sleep  and  waking,  within  the  same 
hour  a  part  may  be  now  very  active  and  then  inactive.  In 
all  its  active  exercise  of  function,  such  a  part  requires  a  larger 
supply  of  blood  than  is  sufficient  for  it  during  the  times  when 
it  is  comparatively  inactive.  It  is  evident  that  the  heart  cannot 
regulate  the  supply  to  each  part  at  different  periods  ;  neither 
could  this  be  regulated  by  any  general  and  uniform  contraction  of 
the  arteries  ;  but  it  may  be  regulated  by  the  power  which  the 
arteries  of  each  part  have,  in  their  muscular  tissue,  of  contracting 
so  as  to  diminish,  and  of  passively  dilating  or  yielding  so  as  to 
permit  an  increase  of  the  supply  of  blood,  according  to  the  require- 
ments of  the  part  to  which  they  are  distributed.  And  thus,  while 
the  ventricles  of  the  heart  determine  the  total  quantity  of  blood, 
to  be  sent  onwards  at  each  contraction,  and  the  force  of  its  pro- 
pulsion, and  while  the  large  and  merely  clastic  arteries  distribute 
it  and  equalise  its  stream,  the  smaller  arteries,  in  addition,  regu- 


I76  CIRCULATION    OF    THE    BLOOD.  [chip.  v. 

late  and  determine,  by  means  of  their  muscular  tissue,  the  propor- 
tion of  the  whole  quantity  of  blood  which  shall  be  distributed  to 
each  part. 

It  must  be  remembered,  however,  that  this  regulating  func- 
tion of  the  arteries  is  itself  governed  and  directed  by  the  nervous 
system  (vaso-motor  centres  and  fibres). 

Another  function  of  the  muscular  element  of  the  middle  coat 
of  arteries  is  (2),  to  co-operate  with  the  elastic  in  adapting  the 
calibre  of  the  vessels  to  the  quantity  of  blood  which  they  contain. 
For  the  amount  of  fluid  in  the  blood-vessels  varies  very  consider- 
ablv  even  from  hour  to  hour,  and  can  never  be  quite  constant; 
and  were  the  elastic  tissue  only  present,  the  pressure  exercised  by 
the  walls  of  the  containing  vessels  on  the  contained  blood  would 
be  sometimes  very  small,  and  sometimes  inordinately  great.  The 
presence  of  a  muscular  element,  however,  provides  for  a  certain 
unifomiitv  in  the  amount  of  pressure  exercised  ;  and  it  is  by  this 
adaptive,  uniform,  gentle,  muscular  contraction,  that  the  normal 
tone  of  the  blood-vessels  is  maintained.  Deficiency  of  this  tone  is 
the  cause  of  the  soft  and  yielding  pulse,  and  its  unnatural  excess, 
of  the  hard  and  tense  one. 

The  elastic  and  muscular  contraction  of  an  artery  may  also  be 
regarded  as  fulfilling  a  natural  purpose  when  (3),  the  artery  being- 
cut,  it  first  limits  and  then,  in  conjunction  with  the  coagulated 
fibrin,  arrests  the  escape  of  blood.  It  is  only  in  consequence  of 
such  contraction  and  coagulation  that  we  are  free  from  danger 
through  even  verv  slight  wounds  ;  for  it  is  only  when  the  artery 
is  closed  that  the  processes  for  the  more  permanent  and  secure 
prevention  of  bleeding  are  established. 

(4)  There  appears  no  reason  for  supposing  that  the  muscular 
coat  assists,  to  more  than  a  very  small  degree,  in  propelling  the 
onward  current  of  blood. 

(1.)  When  a  small  artery  in  the  living  subject  is  exposed  to  the  air  or 
cold,  it  gradually  but  manifestly  contracts.  Hunter  observed  that  the 
posterior  tibial  artery  of  a  dog  when  laid  bare,  became  in  a  short  time  so 
much  contracted  as  almost  to  prevent  the  transmission  of  blood  ;  and  the 
observation  has  been  often  and  variously  confirmed.  Simple  elasticity 
could  not  effect  this. 

(2.)  When  an  artery  is  cut  acro>s.  its  divided  ends  contract,  and  the 
orifices  may  be  completely  closed.  The  rapidity  and  completeness  of  this 
contraction  vary  in  different  animals  ;  they  are  generally  greater  in  young 


v.|  THE     PUIi  i;; 

ipparently,  in  man  than  in  the  lower  animal*, 
ontraction  is  dne  in  pan  .  l>ut   in 

_vnerally  increased  by  the  application  of  cold,  or  of  any 
simple  stimulating  B,  or  by  mechanically  irritating  the  cut  ends  of 

the  artery,  as  by  picking  or  twisting  them. 

1        contractile  property   of   art-  .tinues  many    hours   after 

death,  and  thus  affords  an  opportunity  "f  distinguishing  it  from  thei 

an  artery  of  a  recently  killed  animal  is  exposed, 
mal  may  lx?  thus  completely  clo-ed  :  in  this 
-  for  a  time,  varying  from  a  few  hours  to  two  days  : 
then  it  di  in,  and  permanently  retains  the  same  size. 

-f  the  contractile  property  after  death  wa>  well  si 
in  an  observation  of  Hunter,  whieh  may  be  mentioned  as  proving,  also,  the 
greater  degree  of  •  •untractility  j  assessed  by  the  smaller  than  by  the  larger 
arteries.     Having  injected  the  uterus  of  a  cow.  which  had  been  removed 
from  the  animal  upwar  nty-four  hours,  he  found,  after  the  lapse  of 

another  day.  that  the  larger  vessels  had  become  much  more  turgid  than 
when  he  u  them,  and  that  the  smaller  arteries  had  contracted  so  as  to 

Hon  lia«-k  into  the  larger  • 


The  Pulse. 

If  one  extremity  of  an  elastic  tnbe  In?  fastened  t«.  a  syringe, 
and  the  other  be  bo  constricted  as  i<>  present  an  obstacle  t<>  the 

e  of  fluid,  we  shall  have  a  rough  model  of  what  is  pn 
in  the  livin_  : — -The   syringe  representing  the    heart,   the 

elastic  tube  the  arteries,  and  the  contracted  orifice  the  arterioles 
.lest  art<  b  nd  capillaries.  If  the  apparatus  be  filled  with 
water,  and  if  a  finger-tip  be  placed  on  any  part  of  the  elastic  tube, 
there  will  he  felt  with  every  action  of  the  syringe,  an  impulse  or 
beat,  which  corresponds  exactly  with  what  we  feel  in  the  arteries 
«»f  the  living  body  with  every  contraction  of  the  heart,  and  call  the 
The  pulse  is  essentially  caused  by  an  expans  which 

is  due  to  the  Injection  of  blood  into  an  already  full  aorta  :  which 
blood  expanding  the  vessel  produces  the  pulse  in  it,  almost  coin- 
cideutly  with  the  systole  of  the  left  ventricle.  As  the  force 
of  the  left  ventricle,  however,  is  n<-t  expended  in  dilating  the 
aorta  only,  the  wave  of  blood  |  nei  n,  expanding  the  arteries  as 
it  goes,  running  as  it  were  on  the  surface  of  the  more  slowly 
travelling  blood  already  contained  in  them,  and  producing  the 
pulse  as  it  proceeds. 

The  distension  of  each  artery  increases  both  its  length  and  its 
diameter.     In  their  elongation,  the  arteries  change  their  form,  the 


178  CIRCULATION    OF    THE    BLOOD.  [chap.  v. 

straight  ones  becoming  slightly  curved,  and  those  already  curved 
becoming  more  so,  but  they  recover  their  previous  form  as  well  as 
their  diameter  when  the  ventricular  contraction  ceases,  and  their 
elastic  walls  recoil.  The  increase  of  their  .curves  which  accom- 
panies the  distension  of  arteries,  and  the  succeeding  recoil,  may  be 
well  seen  in  the  prominent  temporal  artery  of  an  old  person.  In 
feeling  the  pulse,  the  finger  cannot  distinguish  the  sensation  pro- 
duced by  the  dilatation  from  that  produced  by  the  elongation  and 
curving  ;  that  which  it  perceives  most  plainly,  however,  is  the 
dilatation,  or  return,  more  or  less,  to  the  cylindrical  form,  of  the 
artery  which  has  been  partially  flattened  by  the  finger. 

The  pulse — due  to  any  given  beat  of  the  heart — is  not  per- 
ceptible at  the  same  moment  in  all  the  arteries  of  the  body. 
Thus, — it  can  be  felt  in  the  carotid  a  very  short  time  before  it  is 
perceptible  in  the  radial  artery,  and  in  this  vessel  again  before  the 
dorsal  artery  of  the  foot.  The  delay  in  the  beat  is  in  proportion 
to  the  distance  of  the  artery  from  the  heart,  but  the  difference  in 
time  between  the  beat  of  any  two  arteries  never  exceeds  probably 
-|  to  -i  of  a  second. 

A  distinction  must  be  carefully  made  between  the  passage  of 
the  wave  along  the  arteries,  and  the  velocity  of  the  stream  (p.  206) 
of  blood.  Both  wave  and  current  are  present  ;  but  the  rates  at 
which  they  travel  are  very  different ;  that  of  the  wave  16*5  to  33 
feet  per  second  (5  to  10  metres),  being  twenty  or  thirty  times 
as  great  as  that  of  the  current. 

The  Sphygmograph. — A  great  deal  of  light  has  been  thrown 
on  what  may  be  called  the  form  of  the  pulse  by  the  sphygmograph 
(figs.  124  and  125).  The  principle  on  which  the  sphygmograph  acts 
is  very  simple  (see  fig.  124).  The  small  button  replaces  the  finger 
in  the  act  of  taking  the  pulse,  and  is  made  to  rest  lightly  on  the 
artery,  the  pulsations  of  which  it  is  desired  to  investigate.  The 
up-and-down  movement  of  the  button  is  communicated  to  the 
lever,  to  the  hinder  end  of  which  is  attached  a  slight  spring,  which 
allows  the  lever  to  move  up,  at  the  same  time  that  it  is  just  strong 
enough  to  resist  its  making  any  sudden  jerk,  and  in  the  interval 
of  the  beats  also  to  assist  in  bringing  it  back  to  its  original 
position.  For  ordinary  purposes  the  instrument  is  bound  on  the 
wrist  (fig.  125). 

It  is  evident  that  the  beating  of  the  pulse  with  the  reaction  of 


CHAP.   \  .  | 


THE    SPHYGMOGRAPH. 


*79 


the  Bpring  will  cans.'  an  up-and-down  movement  of  the  lever,  the 
pen  of  which  will  write  the  effect  on  a  Bmoked  card,  which   is 


T 


BUTTOH. 

Fig.  124. — Diagram  oftht  mode  0/ action  of  (he  Bphy autograph. 

made  to  move  by  clockwork  in  the  direction  of  the  arrow.     Thus 
a  tracing  of  the  pulse  is  obtained,  and  in   this  way  much  more 


Fig.  125. — The  Sphyrjmograph  applied  to  the  arm. 

delicate  effects  can  be  seen,  than  can  be  felt  on  the  application  of 
the  finger. 

The  pulse-tracing  differs  somewhat  according  to  the  artery  upon 
which  the  sphygmograph  is  applied,  but  its  general  characters 
are  much  the  same  in  all  cases.  It  consists  of : — A  sudden 
upstroke  (fig.  126,  a),  which  is  somewhat  higher  and  more  abrupt 
in  the  pulse  of  the  carotid  and  of  other  arteries  near  the  heart 
than  in  the  radial  and  other  arteries  more  remote  ;  and  a  gradual 
decline  (b),  less  abrupt,  and  therefore  taking  a  longer  time  than 
(a).  It  is  seldom,  however,  that  the  decline  is  an  uninterrupted 
fall :  it  is  usually  marked  about  half-way  by  a  distinct  notch  (c), 
called  the  dicrotic  notch,  which  is  caused  by  a  second  more  or  less 
marked  ascent  of  the  lever  at  that  point  by  a  second  wave  called 
the  dicrotic  wave  (d)  ;  not  unfrequently  (in  which  case  the  tracing 

x  3 


l8o  CIRCULATION    OF    THE    BLOOD.  [.  hap.  v. 

is  said  to  have  a  double  apex)  there  is  also  soon  after  the  com- 
mencement of  the  descent  a  slight  ascent  previous  to  the  dicrotic 

notch,  this  is  called  the  pre- 
dicrotic  "-'ire  (c),  and  in  addi- 
tion there  may  be  one  or  more 
Blight  ascents  after  the  dicro- 
tic, called  post  dicrotic  (e). 

The  explanation  of  these 
tracings  presents  some  difficul- 
ties, not,  however,  as  regards 
the  two  primary  factors,  viz., 

Fisr.   126. — Diagram   of  pidse-tradnff.      a,  .-,  ■,  -,    -,  -, 

npetroke;  b,  down-stroke;  ■-,  predi-  the  upstroke  and  downstroke, 

erotic-    -wave;     d,    dicrotic;     e,    post  i  ^i  n 

dicrotic  wave.  because  they  are  universally 

taken  to  mean  the  sudden 
injection  of  blood  into  the  already  full  arteries,  and  that  this 
passes  through  the  artery  as  a  wave  and  expands  them,  the 
gradual  fall  of  the  lever  signifying  the  recovery  of  the  arteries  by 
their  recoil.  It  may  be  demonstrated  on  a  system  of  elastic  tubes, 
such  as  was  described  above,  where  a  syringe  pumps  in  water  at 
regular  intervals,  just  as  well  as  on  the  radial  artery,  or  on  a  more 
complicated  system  of  tubes  in  which  the  heart,  the  arteries,  the 
capillaries  and  veins  are  represented,  which  is  known  as  an  arterial 
schema.  If  we  place  two  or  more  sphygmographs  upon  such  a 
system  of  tubes  at  increasing  distances  from  the  pump,  we  may 
demonstrate  that  the  rise  of  the  lever  commences  first  in  that 
nearest  the  pump,  and  is  higher  and  more  sudden,  while  at  a  longer 
distance  from  the  pump  the  wave  is  less  marked,  and  a  little  later. 
So  in  the  arteries  of  the  body  the  wave  of  blood  gradually  gets  less 
and  less  as  we  approach  the  periphery  of  the  arterial  system, 
and  is  lost  in  the  capillaries.  By  the  sudden  injection  of  blood 
two  distinct  waves  are  produced,  which  are  called  the  tidal 
and  percussion  waves.  The  tidal  wave  occurs  whenever  fluid  is 
injected  into  an  elastic  tube  (fig.  127,  b),  and  is  due  to  the  expan- 
sion of  the  tube  and  its  more  gradual  collapse.  The  percussion 
wave  occurs  (fig.  127,  a)  when  the  impulse  imparted  to  the  fluid  is 
more  sudden ;  this  causes  an  abrupt  upstroke  of  the  lever,  which 
then  falls  until  it  is  again  caught  up  perhaps  by  the  tidal  wave 
which  begins  at  the  same  time  but  is  not  so  quick. 

In  this  way,  generally  speaking,  the   apex  of  the   upstroke  is 


PULSE-TRAI  . 


l8l 


double,    th< 

tion  of  the  I  -         ti'lal  **▼«■     '' 


Fig.  127.— Diagram  of  the  formation  of  the  puU—  A.   I  EI      »  B>  tidal 

wave ;  C,  dicrotic  wave.      Mahonied. 

is  most  marked  in  tracings  from  I  rg       rteries,  especially  when 
their   tone    is  deficient.     In  tracings,   on   the    other   hand,  from 


fig.  i:.  —  1 


toJ  artery,  somewhat  deficient  in  tone.     (Sander -11. 


Arteries  of  medium  b      .   -,  ..  'he  radial,  the  upstroke     a      snally 
single.     In  this  "  asion-impnlse   is   not  sufficiently 


-'  radial  aritry,  with  double  apex,     ^sanaeraocj 

■trong  to  jerk  up  the  lever  and  produce  an  effect  distinct  from 
that    of    the    systolic    I  hich    immediately    follows    it.    and 


1 82  CIRCULATION    OF    THE    BLOOD.  [chap.  v. 

which  continues  and  completes  the  distension.  In  cases  of  feeble 
arterial  tension,  however,  the  percussion-impulse  may  be  traced  by 
the  sphygmograph,  not  only  in  the  carotid  pulse,  but  to  a  less 
extent  in  the  radial  also  (fig.  129). 

The  interruptions  in  the  downstroke  are  called  the  hatacrotic 
waves,  to  distinguish  them  from  an  interruption  in  the  upstroke, 
called  the  anacrotic  wave,  which  is  occasionally  met  with  in  cases 
in  which  the  predicrotic  or  tidal  wave  is  higher  than  the  percus- 
sion wave. 


Fig.  130. — Anna-otic  pulse  from  a  case  of  aortic  aneurism.    A,  anacrotic  wave  (or  percussion 
wave).    B,  tidal  or  predicrotic  wave,  continued  rise  in  tension  (or  higher  tidal  wave). 

There  is  considerable  difference  of  opinion  as  to  whether  the 
dicrotic  wave  is  present  in  health  generally,  and  also  as  to  its 
cause.  The  balance  of  opinion  appears  to  be  in  favour  of  the 
belief  of  its  presence  in  health,  although  it  may  be  very  faint  ; 
while,  at  any  rate,  in  certain  conditions  not  necessarily  diseased,  it 
becomes  so  marked  as  to  be  quite  plain  to  the  unaided  finger. 
Such  a  pulse  is  called  dicrotic.  Sometimes  the  dicrotic  rise 
exceeds  the  initial  upstroke,  and  the  pulse  is  then  called  hyper- 
dicrotic. 

As  to  the  cause  of  dicrotism,  one  opinion  is  that  it  is  due  to  a 
recovery  of  pressure  during  the  elastic  recoil,  in  consequence  of  a 
rebound  from  the  periphery,  and  it  may  indeed  be  produced  on  a 
schema  hj  obstructing  the  tube  at  a  little  distance  beyond  the 
spot  where  the  sphygmograph  is  placed.  Against  this  view,  how- 
ever, is  the  fact  that  the  notch  appears  at  about  the  same  point  in 
the  downstroke  in  tracings  from  the  carotid  and  from  the  radial, 
and  not  first  in  the  radial  tracing,  as  it  should  do,  since  that 
artery  is  nearer  the  periphery  than  the  carotid,  and  as  it  does  in 
the  corresponding  experiment  with  the  arterial  schema  when  the 
tube  is  obstructed.  The  generally  accepted  notion  among  clinical 
observers,  is  that  the  dicrotic  wave  is  due  to  the  rebound  from  the 
aortic  valves  causing  a  second  wave  ;  but  the  question  cannot  be 


CHAP,   v.  I 


ITISK-'I  aACINGS. 


183 


considered  settled,  and  the  presenoe  of  marked  dicrotism  in  1 
of  haemorrhage,  of  anaemia,  and  of  other  weakening  conditions,  as 
well  as  its  presence  in  eases  of  diminished  pressure  within  the 

arteries,  would  imply  that  it  might,  at  any  rate  sometimes,  be  due 


&K3S?  3,  dicr^fcpuEe  ": 4  aAdP5,  the  tidal  wave  very  exaggerated,  from 
high  tension.     (Mahomed.) 

to  the  altered  specific  gravity  of  the  blood  within  the  vessels, 
either  directly  or  through  the  indirect  effect  of  these  conditions 
on  the  tone  of  the  arterial  walls.  Waves  may  be  produced  in 
any  elastic  tube  when  a  fluid  is  being  driven  through  it  with  an 


1 84  CIRCULATION    OF    THE    BLOOD.  [ohap,  v. 

intermittent  force,  such  waves  being  called  waves  of  oscillation 
(M.  Foster).  They  have  received  various  explanations.  In  an 
arterial  schema  they  vary  with  the  specific  gravity  of  the  fluid 
used,  and  with  the  kind  of  tubing,  and  may  be  therefore  supposed 
to  vary  in  the  body  with  the  condition  of  the  blood  and  of  the 
arteries. 

Some  consider  the  secondary  waves  in  the  downstroke  of  a  normal 
wave  to  be  due  to  oscillation  ;  but,  as  just  mentioned,  even  if 
this  be  the  case,  as  is  most  likely,  with  post-dicrotic  waves,  the 
dicrotic  wave  itself  is  almost  certainly  due  to  the  rebound  from 
the  aortic  valves. 

The  anacrotic  notch  is  usually  associated  with  disease  of  the 
arteries,  e.g.,  in  atheroma  and  aneurism.  The  dicrotic  notch 
is  called  diastolic  or  aortic,  and  indicates  closure  of  the  aortic 
valves. 

Of  the  three  main  parts  then  of  a  pulse-tracing,  viz.,  the  per- 
cussion wave,  the  tidal,  and  the  dicrotic,  the  percussion  wave  is 
produced  by  sudden  and  forcible  contraction  of  the  heart,  perhaps 
exaggerated  by  an  excited  action,  and  may  be  transmitted  much 
more  rapidly  than  the  tidal  wave,  and  so  the  two  may  be  distinct ; 
frequently,  however,  they  are  inseparable.  The  dicrotic  wave 
may  be  as  great  or  greater  than  the  other  two. 

According  to  Mahomed,  the  distinctness  of  the  three  waves 
depends  upon  the  following  conditions  : — 

The  jiercussion  wave  is  increased  by  : — i.  Forcible  contraction 
of  the  Heart :  2.  Sudden  contraction  of  the  Heart  :  3.  Large 
volume  of  blood  ;  4.  Fulness  of  vessel  ;  and  diminished  by  the 
reversed  conditions. 

The  tidal  wave  is  increased  by  : — 1.  Slow  and  prolonged  con- 
traction of  the  Heart;  2.  Large  volume  of  blood;  3.  Comparative 
emptiness  of  vessels ;  4.  Diminished  outflow  or  slow  capillary 
circulation ;  and  diminished  by  the  reversed  conditions. 

The  dicrotic  wave  is  increased  by  : — 1.  Sudden  contraction  of 
the  Heart  ;  2.  Comparative  emptiness  of  vessels  ;  3.  Increased 
outflow  or  rapid  capillary  circulation  ;  4.  Elasticity  of  the  aorta  ; 
5.  Relaxation  of  muscular  coat;  and  diminished  by  the  reversed 
conditions. 

One  very  important  precaution  in  the  use  of  the  sphygmograph 
lies  in  the  careful  regulation  of  the  pressure.     If  the  pressure  be 


I  KAP.    v.  | 


ARTERIAL    TENSION. 


18. 


too  great,   khe  oharacters  of  bhe  pulse  may   be  almosl  entirely 
obscured,  or  the  arterj  may  be  entirely  obstructed,  and  qo  tracing 

is  obtained  ;   and  mi  the  other  hand,  if  the  pressure   be  too  Blight, 

a  verv  small   part  of  the  characters  maj   be  represented   on   the 
tracing. 


The  Pressure  of  the  Blood  within  the  Arteries  (producing 

arterial  tension). 

It  will  be  understood  from  the  foregoing  that  the  arteries  in  a 
norma]  condition,  are  continually  on  the  stretch  during  life,  and 
in  consequence  of  the  injection  of  more  Mood  at  each  systole 
of  the  ventricle  into  the  elastic  aorta,  this 
stretched  condition  is  exaggerated  each  time 
the  ventricle  empties  itself.  This  condition 
of  the  arteries  is  due  to  the  pressure  of  blood 
within  them,  because  of  the  resistance  pre- 
sented by  the  smaller  arteries  and  capillaries 
(peripheral  resistance)  to  the  emptying  of  the 
arterial  system  in  the  intervals  between  the 
contractions  of  the  ventricle,  and  is  called  the 
condition  of  arterial  tension.  On  the  other 
hand,  it  must  be  equally  clear  that,  as  the 
blood  is  forcibly  injected  into  the  already  full 
arteries  against  their  elasticity,  it  must  be 
subjected  to  the  pressure  of  the  arterial  walls, 
the  elastic  recoil  sending  on  the  blood  after 
the  immediate  effect  of  the  systole  has  passed  ; 
so  that,  when  an  artery  is  cut  across,  the 
blood  is  projected  forwards  by  this  force  for 
a  considerable  distance  ;  at  each  ventricular 
systole,  a  jet  of  blood  escaping,  although 
the  stream  does  not  cease  flowing  during 
the  diastole. 

The  relations  which  exist  between  the  arte-   ' IL 
ries  and  their  contained  blood  are  obviously 

of  the  utmost  importance  to  the  carrying  on  of  the  circulation, 
and  it  therefore  becomes  necessary  to  be  able  to  gauge  the 
alterations  in  blood-pressure  very  accurately.  This  may  be  done 
by  means  of  a  mercurial   manometer  in  the  following  way  : — The 


132. — Diagram  of  mer- 
curial »"-    """  U  r. 


i86 


CIRCULATION    OF    THE    BLOOD. 


[chap.  v. 


short  horizontal  limb  of  this  (fig.  132,  1)  is  connected,  by  means 
of  an  elastic  tube  and  cannula,  with  the  interior  of  an  artery  ; 
a  solution  of  sodium  or  potassium  carbonate  being  previously  intro- 
duced into  this  part  of  the  apparatus  to  prevent  coagulation  of  the 
blood.  The  blood-pressure  is  thus  communicated  to  the  upper 
part  of  the  mercurial  column  (2);  and  the  depth  to  which  the 
latter  sinks,  added  to  the  height  to  which  it  rises  in  the  other  (3), 
will  give  the  height  of  the  mercurial  column  which  the  blood- 
pressure  balances;  the  weight  of  the  soda  solution  being  sub- 
tracted. 


Fig.  1.53. — Diagram  of  mercurial  kymograph,     a.  revolving  cylinder,  worked  by  a  clockwork 

arrangement  contained  in  the  box  (b),  the  speed  being  regulated  by  a  fan  above  the 
box  ;  cylinder  supported  by  an  upright  [b),  and  capable  of  being  raised  or  lowered  by 
a  screw  [a),  by  a  handle  attached  to  it;  d,  c,  e,  represent  mercurial  manometer,  a 
somewhat  different  form  of  which  is  shown  in  next  figure. 


For  the  estimation  of  the  arterial  tension  at  any  given  moment, 
no  further  apparatus  than  this,  which  is  called  Poiseuille's 
hcemo.d<jna  1  no) ader,  is  necessary ;    but  for  noting  the   variations  of 


i  HAP.   v.  | 


BL00D-PRE8SURE. 


IS/ 


pressure  in  the  arterial  Bystem,  as  well  as  it-  absolute  amount,  the 
instrumenl  is  usually  combined  with  a  registering  apparatus  and 
in  this  form  is  called  a  kymograph. 

The  kymograph,  invented  byLudwig,  is  composed  of  a  hsemady 
namometer,  the  open  mercurial  column  of  which  supports  a  float- 
ing   piston    and    vertical     r<»»l,    with 
short  horizontal  pen  (fig.  134).     The 
pen   is  adjusted  in  contact  with   a 

sheet    of  paper,    which    is    caused    to 

move  at  an  uniform  rate  by  clock- 
work :  and  thus  the  up-and-down 
movements  of  the  mercurial  column, 
which  are  communicated  to  the  rod 

and  pen,  are  marked  or  registered  on 
the  moving  paper,  as  in  the  regis- 
tering apparatus  of  the  sphygmo- 
graph,  and  minute  variations  are 
graphically  recorded  (fig.  135). 

For  some  purposes  the  spring 
kymograph  of  Fick  (fig.  136)  is  pre- 
ferable  to  the  mercurial  kymograph. 
It  consists  of  a  hollow  C-shaped 
spring,  rilled  with  fluid,  the  interior 
of  which  is  brought  into  connection 
with  the  interior  of  an  artery,  by 
means  of  a  flexible  metallic  tube 
and  cannula.  In  response  to  the 
pressure  transmitted  to  its  interior,  the  spring,  c,  tends  to 
straighten   itself,  and  the  movement  thus  produced  is  communi- 


Fig.  134. — Diagram  ofnu  rcurial  mano- 
meter, a.  Floating  rod  and  pen. 
I).  Tube,  which  communicates 
with  a  bottle  containing  an  alka- 
line solution,  c' .  Elastic  tube  and 
cannula,  the  latter  being  intended 
for  insertion  in  an  arterv. 


Fig-  *35- — Normal  tracing  of  arterial  pressure  in  the  rabbit  obtained  with  the  mercurial 

kymograph.     The  smaller  undulations  correspond  -with  the  heart  beats;   tin-  larger 
curves  with  the  respiratory  movements.    (Burdon-Sanderson.) 


cated  by  means  of  a  lever,  6,  to  a  writing-needle  and  registering 
apparatus. 


188 


CIRCULATION    OF    THE    BLOOD. 


[chap.  v. 


Fig.  137  exhibits  an  ordinary  arterial  pulse-tracing,  as  obtained 
by  the  spring-kymograph. 

From  observations  which  have  been  made  by  means  of  the 
mercurial  manometer,  it  has  been  found  that  the  pressure  of  blood 
in  the  carotid  of  a  rabbit   is  capable  of  supporting  a  column  of 

2  to  3 1  inches  (50  to 
90  mm.),  of  mercury, 
in  the  dog  4  to  7  inches 
(100  to  175  mm.),  in 
the  horse  5  to  8  inches 
( 1 5 o  to  200  mm. ),  and 
in  man  about  the 
same. 

To  measure  the 
absolute  amount  of 
this  pressure  in  any 
artery,  it  is  necessary 
merely  to  multiply 
the  area  of  its  trans- 
verse section  by  the 
height  of  the  column 
of  mercury  which  is 
already  known  to  be 
supported  by  the 
blood-pressure  in  any 
part    of  the    arterial 

Pig.  136.— A  for,,}  of  Fide s  Spring  Kymograph.    a,  tube  to  system.      The  weight 

be  connected  -with  artery ;  c,  hollow  spring,  the  move-  _ 

ment  of  which  moves  6,  the  writing  lever  ;  e,  screw  to  of  a    column    of  mer- 

regulate    height  of  h ;    d,  outside    protective    spring;  0          . 

!/,  screw  to  fix  on  the  upright  of  the  support.  CUry  thllS    IOUlld    Will 

represent  the  pressure 
of  the  blood.  Calculated  in  this  way,  the  blood-pressure  in  the 
human  aorta  is  equal  to  4  lb.  4  oz.  avoirdupois  ;  that  in  the 
aorta  of  the  horse  being  11  lb.  9  oz. ;  and  that  in  the  radial  artery 
at  the  human  wrist  only  4  drs.  Supposing  the  muscular  power  of 
the  right  ventricle  to  be  only  one-half  that  of  the  left,  the  blood- 
pressure  in  the  pulmonary  arteiy  will  be  only  2  lb.  2  oz.  avoir- 
dupois. The  amounts  above  stated  represent  the  arterial  tension 
at  the  time  of  the  ventricular  contraction. 

The  blood-pressure  is  greatest  in  the  left  ventricle  and  at  the 


1 


i  hat.  \.|  BLOOD-PRE88URE,  ^q 

banning  of  the  aorta,  and  decreases  towards  the  capillaries.  It 
is  greatest  in  the  arteries  at  the  period  of  the  ventricular  systole, 
and  is  least  in  the  auricles,  during  diastole,  when  the  pressure  there 
and  iii  the  great  veins  becomes,  as  we  have  Been,  negative.     The 


Fig.  137.- -Normal  arterial  tracing  obtained  with  Fick's  kymograph  in  the  dog.  (Burdon- 

-   nderson.) 


mean  arterial  pressure  equals  the  average  of  the  pressures  in  all 
the  arteries.  The  pressure  in  the  veins  is  never  more  than  one- 
tenth  of  the  pressure  in  the  corresponding  arteries  and  is  greatest 
at  the  time  of  auricular  systole.  There  is  no  periodic  variation 
in  venous  pressure,  as  there  is  in  the  arterial,  except  in  the  great 
veins. 

Variations  of  Blood- Pressure.— Many  circumstances  cause 
considerable  variations  in  the  amount  of  the  blood-pressure.  The 
following  are  the  chief: — (1)  Changes  in  the  beat  of  the  Heart; 
(2)  Changes  in  the  Arteries  and  Capillaries;  (3)  Changes  due  to 
Nerve  Action;  (4)  Changes  in  the  Blood;  (5)  Respiratory  Changes. 

1.  Changes  in  the  Beat  of  the  Heart. — The  systole  and  diastole 
of  the  muscular  chambers.  The  arterial  tension  increases  duriiiLi 
systole  and  diminishes  during  diastole.  The  greater  the  fre- 
quency, moreover,  of  the  heart's  contractions,  the  greater  is  the 
blood-pressure,  ceeteris  paribus  ;  although  this  effect  is  not  con- 
stant, as  it  may  be  compensated  for  by  the  delivery  into  the 
arteries  at  each  beat  of  a  comparatively  small  quantity  of  blood. 
The  greater  the  quantity  of  blood  expelled  from  the  heart  at  each 
contraction  the  greater  is  the  blood-pressure. 

The  quantity  and  quality  of  the  blood  nourishing  the  heart's 
substance  through  the  coronary  arteries  must  exercise  also  a  very 
considerable  influence  upon  its  action,  and  therefore  upon  the 
blood-pressure. 

2.  Clianges  in  the  Arteries  and  Capillaries. — Variations  in  the 
degree  of  contraction  of  the  smaller  arteries  modify  the  blood- 


190  CIRCULATION    OF    THE    BLOOD.  [chap.  v. 

2)ressure  by  favouring  or  impeding  the  accumulation  of  blood  in 
the  arterial  system  which  follows  every  contraction  of  the  heart ; 
the  contraction  of  the  arterial  walls  increasing  the  blood-pressure, 
while  their  relaxation  lowers  it. 

3.  Changes  due  to  Nerve  Action. — As  with  the  heart,  so  with  the 
blood-vessels  the  action  of  the  nervous  system  is  very  important  in 
relation  to  the  blood-pressure ;  regulating,  as  it  does,  not  only  the 
force,  frequency,  and  length  of  the  heart's  systole,  but  also  the 
condition  of  the  arteries,  both  through  the  central  and  peripheral 
vaso-motor  centres.  As  this  subject  has  not  yet  been  fully  con- 
sidered it  will  be  as  well  to  treat  of  it  here. 

It  is  upon  the  muscular  coat  of  the  arteries  that  the  nervous 
system  exercises  its  influence  ;  the  elastic  element  possessing,  as 
must  be  obvious,  rather  physical  than  vital  properties.  The 
muscular  tissue  in  the  walls  of  the  vessels  increases  relatively  to 
the  other  coats  as  the  arteries  grow  smaller,  so  that  in  the 
smallest  arteries  it  is  developed  out  of  all  proportion  to  the  other 
elements  ;  in  fact,  in  passing  from  capillary  vessels,  made  up  as 
we  have  seen  of  endothelial  cells  with  a  ground  substance,  the 
first  change  which  occurs  as  the  vessels  become  larger  (on  the  side 
of  the  arteries)  is  the  appearance  of  muscular  fibres.  Thus  the 
nervous  system  is  more  powerful  in  regulating  the  calibre  of  the 
smaller  than  of  the  larger  arteries. 

It  has  been  shown  that  if  the  cervical  sympathetic  nerve  be 
divided  in  a  rabbit,  the  blood-vessels  of  the  corresponding  side 
become  dilated.  The  effect  is  best  seen  in  the  ear,  which  if  held 
up  to  the  light  is  seen  to  become  redder,  and  the  arteries  to 
become  larger.  The  whole  ear  is  distinctly  warmer  than  the 
opposite  one.  This  effect  is  produced  by  removing  the  arteries 
from  the  influence  of  the  central  nervous  system,  which  influence 
usually  passes  down  the  divided  nerve  ;  for  if  the  peripheral  end  of 
the  divided  nerve  {i.e.,  that  farthest  from  the  brain)  be  stimulated, 
the  arteries  which  were  before  dilated  return  to  their  natural  size, 
and  the  parts  regain  their  primitive  condition.  And,  besides  this,  if 
the  stimulus  which  is  applied  be  too  strong  or  too  long  continued, 
the  point  of  normal  constriction  is  passed,  and  the  vessels  become 
much  more  contracted  that  normal.  The  natural  condition,  which 
is  somewhere  about  midway  between  extreme  contraction  and 
extreme  dilatation,  is  called  the  natural  tone  of  an  artery,  and  if 


chap,  v.]  VA80-M0T0R    SYSTEM.  191 

this  be  not  maintained,  the  vessel  Is  Baid  to  nave  lost  tone,  or  if  it 
be  exaggerated,  the  tone  is  Baid  to  be  too  great.     The  influent 
the  nervous  Bvstem   upon  the   vessels  consists  in  maintains 
natural  tone.     The  effects  described  as  haying  been  produced  by 


Fig.  138— PUthysmograph.  By  means  of  this  apparatus,  the  alteration  in  volume  of  the 
arm,  B,  which  is  enclosed  in  a  glass  tube,  a,  filled  -with  fluid,  the  opening  through 
which  it  passes  being  firmly  closed  by  a  thick  gutta  percha  band,  p,  is  communi 
to  the  lever,  n.  and  registered  by  a  recording  apparatus.  The  fluid  in  a  communi 
■with  that  in  n.  the  upper  limit  of  which  is  above  that  in  a.  The  chief  alterations 
in  volume  are  due  to  alteration  in  the  blood  contained  in  the  arm.  When  the  volume 
is  increased,  fluid  passes  out  of  the  glass  cylinder,  and  the  lever,  d,  also  is  raised,  and 
when  a  decrease  takes  place  the  fluid  returns  again  from  b  to  a.  It  will  therefore  be 
evident  that  the  apparatus  is  capable  of  recording  alterations  of  blood-pressure  in  the 
arm.  Apparatus  founded  upon  the  same  principle  have  been  used  for  recording  alte- 
rations in  the  volume  of  the  spleen  and  kidney. 


section  of  the  cervical  sympathetic  and  by  subsequent  stimulation 
are  not  peculiar  to  that  nerve,  as  it  has  been  found  that  for  every 
part  of  the  body  there  exists  a  nerve  the  division  of  which  pro- 
duces the  same  effects,  viz.,  dilatation  of  the  arteries  ;  such  may 
be  cited  as  the  case  with  the  sciatic,  the  splanchnic  nerves,  and  the 
nerves  of  the  brachial  plexus  :  when  divided,  dilatation  of  the 
blood-vessels  in  the  parts  supplied  by  them  taking  place.  It 
appears,  therefore,  that  nerves  exist  which  have  a  distinct  control 
over  the  vascular  supply  of  a  part. 

These  nerves,  are  called  v<  1  so-motor ;  or,  since  they  seem  to  run 
now  in  cerebro- spinal  nerves,  now  in  the  sympathetic,  we  speak  of 
those  nerves  as  containing  vasomotor  fibres,  in  addition  to  the 
fibres  which  have  other  functions. 

Vaso-motor  centres.— Experiments  by  Ludwig  and  others 
show  that  the  vaso-motor  fibres  come  primarily  from  grey  matter 


192  CIRCULATION    OF    THE    BLOOD.  [chap.  v. 

(vaso-motor  centre)  in  the  interior  of  the  medulla  oblongata, 
between  the  calamus  scriptorius  and  the  corpora  quadrigemina. 
Thence  the  vaso-motor  fibres  pass  down  in  the  interior  of  the 
spinal  cord,  and  issuing  with  the  anterior  roots  of  the  spinal 
nerves,  traverse  the  various  ganglia  on  the  prae-vertebral  cord  of 
the  sympathetic,  and,  accompanied  by  branches  from  these  ganglia, 
pass  to  their  destination. 

Secondary  or  subordinate  centres  exist  in  the  spinal  cord,  and 
local  centres  in  various  regions  of  the  body,  and  through  these, 
directly  under  ordinary  circumstances,  vaso-motor  changes  are 
also  effected. 

The  influence  exerted  by  the  chief  vaso-motor  centre  is  called 
into  play  in  several  ways,  bnt  chiefly  by  afferent  (sensory)  stimuli, 
and  it  may  be  exerted  in  two  ways,  either  to  increase  its  usual 
action  which  maintains  a  medium  tone  of  the  arteries  or  to 
diminish  such  action.  This  afferent  influence  upon  the  centre 
may  be  extremely  well  shown  by  the  action  of  a  nerve  the  exist- 
ence of  which  was  demonstrated  by  Cyon  and  Ludwig,  and  which 
is  called  the  depressor,  because  of  its  characteristic  influence  on  the 
blood-pressure. 

Depressor  Nerve. — This  small  nerve  arises,  in  the  rabbit,  from 
the  superior  laryngeal  branch,  or  from  this  and  the  trunk  of  the 
pneumogastric  nerve,  and  after  communicating  with  filaments  of 
the  inferior  cervical  ganglion  proceeds  to  the  heart. 

If  during  an  observation  of  the  blood-pressure  of  a  rabbit  this 
nerve  be  divided,  and  the  central  end  (i.e.,  that  nearest  the 
brain)  be  stimulated,  a  remarkable  fall  of  blood-pressure  ensues 

(%  J39)- 

The    cause  of  the  fall  of  blood-pressure  is  found  to  proceed  from 

the  dilatation  of  the  vascular  district  supplied  by  the  splanchnic- 
nerves,  in  consequence  of  which  it  holds  a  much  larger  quantity 
of  blood  than  usual,  and  this  very  greatly  diminishes  the  blood 
in  the  vessels  elsewhere,  and  so  materially  affects  the  blood- 
pressure.  This  effect  of  the  depressor  nerve  is  presumed  to  prove 
that  the  nerve  is  a  means  of  conveying  to  the  vaso-motor  centre 
indications  of  such  conditions  of  the  heart  as  require  a  diminution 
of  the  tension  in  the  blood-vessels ;  as,  for  example,  when  the 
heart  cannot,  with  sufficient  ease,  propel  blood  into  the  already 
too  full  or  too  tense  arteries. 


CHAP,  v.] 


DEPEESSOB    NERVE, 


193 


The  aotion  of  the  depressor  oerve  illustrates  fche  effeoi  of 
afferent  impulses  in  causing  an  inhibition  of  the  vaso-motor  centre 
as  regards  its  action  upon   certain  arteries.     There  exisl   other 

nerves,  however,  the  stimulation  of  the  Central  <in<l  of  which  causes 


Fig.  139. —  Trannr/  showing  the  effect  on  blood-pressure  of  stimulating  the  central  end  of  the 
Depressor  nerve  in  the  rabbit.  To  be  read  from  right  to  left.  T,  indicates  the  rate  at 
which  the  recording-surface  was  travelling,  the  intervals  coiTespond  to  seconds ; 
C,  the  moment  of  entrance  of  current ;  O,  moment  at  which  it  was  shut  off.  The 
effect  is  some  time  in  developing  and  lasts  after  the  current  has  been  taken  off.  The 
larger  undulations  are  the  respiratory  nerves ;  the  pulse  oscillations  are  very  small. 
(M.  Foster.) 

a  reverse  action  of  the  centre,  or,  in  other  words,  increases  its 
tonic  influence,  and  by  causing  considerable  constriction  of  certain 
arterioles,  either  locally  or  generally,  increases  the  blood-pressure. 
Moreover,  the  effect  of  stimulating  an  afferent  nerve  may  be  to  dilate 
or  constrict  the  arteries  either  generally  or  in  the  part  supplied  by 
the  afferent  nerve ;  and  it  is  said  that  stimulation  of  an  afferent 
nerve  may  produce  a  kind  of  paradoxical  effect,  causing  general 
vascular  constriction  and  so  general  increase  of  blood-pressure  but 
at  the  same  time  local  dilatation.  This  must  evidently  have  an 
immense  influence  in  increasing  the  flow  of  blood  through  a  part. 

Not  only  may  the  vaso-motor  centre  be  reflexly  affected,  but  it 
may  also  be  affected  by  impulses  proceeding  to  it  from  the  cere- 
brum, as  in  the  case  of  blushing  from  mind  disturbance,  or  of 
pallor  from  sudden  fear.  It  will  be  shown,  too,  in  the  chapter  on 
Respiration  that  the  circulation  of  deoxygenated  blood  may 
directly  stimulate  the  centre  itself. 

Local  Tonic  Centres.— Although  the  tone  of  the  arteries  is 
influenced  by  the  centres  in  the  cerebro-spinal  axis,  certain  experi- 


!Q4  CIRCULATION    OF    THE    BLOOD.  [chap.  v. 

meiits  point  out  that  this  is  not  the  only  way  in  which  it  may  be 
affected.  Thus  the  dilatation  which  occurs  after  section  of  the 
cervical  sympathetic  in  the  first  experiment  cited  above,  only 
remains  for  a  short  time,  and  is  soon  followed — although  a  portion 
of  the  nerve  may  have  been  removed  entirely — by  the  vessels  re- 
gaining their  ordinary  calibre ;  and  afterwards  local  stimulation, 
e.g.,  the  application  of  heat  or  cold,  will  cause  dilatation  or 
constriction.  From  this  it  is  probable  that  there  exists  a  local 
mechanism  distinct  for  each  vascular  area,  and  that  the  effect  pro- 
duced by  the  central  nervous  system  acts  through  it  much  in  the 
same  way  as  the  cardio-inhibitory  centre  in  the  medulla  acts  upon 
the  heart  through  the  ganglia  contained  within  its  muscular 
substance. 

Central  impulses  may  inhibit  or  increase  the  action  of  these 
local   centres,  which  may  be   considered  to   be    sufficient  under 
ordinary  circumstances  to  maintain  the  local  tone  of  the  vessels. 
The  observations   upon  the  functions  of  the  vaso-motor  nerves 
appear  to  divide  them  into  four  classes  :    (i)  those  on  division  of 
which  dilatation  occurs  for  some  time,  and  which  on  stimulation  of 
their  peripheral  end  produce  constriction ;  (2)  those  on  division 
of  which  momentary  dilatation  followed  by  constriction  occurs, 
with  dilatation  on  stimulation ;    (3)   those   on   division  of  which 
dilatation  is  caused,  which  lasts  for  a  limited  time,  with  constric- 
tion if  stimulated  at  once,  but  dilatation  if  some  time  is  allowed 
to  elapse  before  the  stimulation  is  applied  :   (4)  a  class,  division  of 
wdiich    produces    no    effect    but    which,     on    stimulation,    cause 
according  to  their  function  either  dilatation  or  constriction.     A 
good  example    of   this  fourth    class   is   afforded   by   the    nerves 
supplying  the  submaxillary  gland,  viz.,  the  chorda  tympani   and 
the  sympathetic.     When  either  of  these  nerves  is  simply  divided, 
no    change   takes   place    in    the   vessels  of   the    gland ;    but  on 
stimulating  the  chorda  tympani  the  vessels  dilate,   and,  on  the 
other  hand,  when  the  sympathetic  is  stimulated  the  vessels  con- 
tract.    The  nerves  acting  like  the  chorda  tympani  in  this  case 
are  called  vaso-dilators,  and  those  like  the  sympathetic   vaso-con- 
strictors.     The  third  class,  which  produce  at  one  time  dilatation, 
at  another  time  constriction,  are  believed  to  contain  both  kinds  of 
vaso-motor  nerve-fibres,  or  to  act  as  dilators  or  contractors  accord- 
ing to  the  condition  of  the  local  apparatus.     It  is  probable  that 


•  map.  v.]  LOCAI    NERVE-CENT]  Ir>5 

I  by  inhibiting  or  augmenting  the  action  of  the 
local  nervous  mechanism  already  referred  to  ;  and  as  th<  y  are  in 
connection  with  the  central   nn-v  tern,  it   i>  through   this 

arrai  I    that   thai  o    i>  capable  "f  innuenci 

maintaining  the  normal  local  tone. 

it  may  also  'I  that  the  local  nerve  i  lv«B 

may  be  directly  affected  by  the  condition  of  blood  nourishing  them. 
The  following  table  may  serve  as  a  summary  of  the  effect  of 
the  nen  stem  upon  the   arteries  and  so  upon   the  blood- 

rare  : — 

A.  An  increase  of  the  blood-pressure  may  be  produced: — 

(i.)  By  stimulation  of  the      -  -     'tor  centre  in  medulla,  either 

a.  J>  ,  as  by  carbonated  or  deoxygenated  blood. 

0.  Indirectly,  by  inipres-ions  descending  from  the  cerebrum, 
.  in  sudden  pallor. 

-,.  Reflexly,  by  stimulation  of  sensory  nerve-  anywhere. 
(2.)  By  stimulation  of  the  centres  in  spinal  cord. 

Possibly  directly  or  indirectly,  certainly  reflexly. 
(3.)  By  stimulation  of  the  local  centres  for  each  vascular  area,  by 

the  vaso-constrictor  nerves,  or  directly  by  means  of  altered 

blood. 

B.  A  decrease  of  the  blood-pressure  may  be  produced : — 

(1.)  By  stimulation  of  the  vaao-motor  centre  in  medulla,  either 
(a.)  Directly,  as  by  oxygenated  or  aerated  blood. 
(£.)  Indirectly,  by  impressions  descending  from  the  cere- 
brum— e.g..  in  blushing. 
(7.)  Reflexly,  by  stimulation  of  the  depressor  nerve,  and 
consequent  dilatation  of  vessels  of   splanchnic  area, 
and  possibly  by  stimulation  of  other  sensory  nen 
the  sensory  impulse  being  interpreted  as  an  indication 
for  diminished  blood-pressure. 
(2.)  By  stimulation  of  the  centres  in  spinal  cordL    Possibly  directly. 

indirectly,  or  reflexly. 
(3.)  By  stimulation  of  local  centres  for  each  vascular  area  by  the 
vaso-dilator  nerve,  or  directly  by  means  of  altered  blood. 

4.  Chan  the   blood  —  a.    As   regards  quantity.      At    rirst 

it  would  appear  that   one  of  the   ea-siest   ways   to  diminish 
the  blood-pressure  would  be   to  remove  blood   from  the   v.  - 
by   bleeding  ;    it  has   been  found  by   experiment,   however,  that 
although   the    blood-pres  bilst    L  stractiona  of 

blood  are  taking   place,  as    soon  as  the  bleeding  ceases  it 
rapidly,  and  Bpeedily  becomes  normal:  that  is  to  say,  mile-  - 
an    amount    of  blood   has   been    taken  as  to  be  positively 

o  2 


196  CIRCULATION    OF    THE    BLOOD.  [chap.  v. 

dangerous  to  life,  abstraction  of  blood  has  little  effect  upon  the 
blood-pressure.  The  rapid  return  to  the  normal  pressure  is  due 
not  so  much  to  the  withdrawal  of  lymph  and  other  fluids  from  the 
body  into  the  blood,  as  was  formerly  supposed,  as  to  the  regu- 
lation of  the  peripheral  resistance  by  the  vaso-motor  nerves ;  in 
other  words,  the  small  arteries  contract,  and  in  so  doing  maintain 
pressure  on  the  blood  and  favour  its  accumulation  in  the  arterial 
system.  This  is  due  to  the  stimulation  of  the  vaso-motor  centre 
from  diminution  of  the  supply  of  blood,  and  therefore  of  oxygen. 
The  failure  of  the  blood-pressure  to  return  to  normal  in  the  too 
great  abstraction  must  be  taken  to  indicate  a  condition  of 
exhaustion  of  the  centre,  and  consequently  of  want  of  regulation 
of  the  peripheral  resistance.  In  the  same  way  it  might  be 
thought  that  injection  of  blood  into  the  already  pretty  full 
vessels  would  be  at  once  followed  by  rise  in '  the  blood-pressure, 
and  this  is  indeed  the  case  up  to  a  certain  point — the  pressure 
does  rise,  but  there  is  a  limit  to  the  rise.  Until  the  amount  of 
blood  injected  equals  about  2  to  3  per  cent,  of  the  body  weight  the 
pressure  continues  to  rise  gradually ;  but  if  the  amount  exceed 
this  proportion,  the  rise  does  not  continue.  In  this  case  therefore, 
as  in  the  opposite  when  blood  is  abstracted,  the  vaso-motor  appa- 
ratus must  counteract  the  great  increase  of  pressure  by  dilating 
the  small  vessels,  and  so  diminishing  the  peripheral  resistance,  for 
after  each  rise  there  is  a  partial  fall  of  pressure  ;  and  after  the 
limit  is  reached  the  whole  of  the  injected  blood  displaces,  as  it 
were,  an  equal  quantity  which  passes  into  the  small  veins,  and 
remains  within  them.  It  should  be  remembered  that  the  veins 
are  capable  of  holding  the  whole  of  the  blood  of  the  body. 

The  amount  of  blood  supplied  to  the  heart  both  to  its  substance 
and  to  its  chambers,  has  a  marked  effect  upon  the  blood-pressure. 

b.  As  regards  quality.  The  quality  of  the  blood  supplied  to  the 
heart  has  a  distinct  effect  upon  its  contraction,  as  too  watery  or 
too  little  oxygenated  blood  must  interfere  with  its  action.  Thus 
it  appears  that  blood  containing  certain  substances  affects  the 
peripheral  resistance  by  acting  upon  the  muscular  fibres  of  the 
arterioles  themselves  or  upon  the  local  centres,  and  so  altering 
directly,  as  it  were,  the  calibre  of  the  vessels. 

5.  Respiratory  changes  affecting  the  blood-pressure  will  be 
considered  in  the  next  Chapter. 


chap,  v.]         CIRCULATION    IN    THE    CAPILLARE  Ujj 

Circulation  in    the    Capillaries. 

When  seefl  in  any  transparent  part  of  a  living  adult  animal 
by  means  of  the  microscope  (fig.  140),  the  blood  flows  with  a 
constant  equable  motion ;  the  red  blood-corpuscles  moving  along, 
mostly  in  single  file,  and  bending  in  various  ways  to  accom- 
modate themselves  to  the  tortuous  course  of  the  capillary,  but 
instantly  recovering  their  normal  outline    on    reaching   a  wider 

seL 

It  is  in  the  capillaries  that  the  chief  resistance  is  offered  to  the 
progress  of  the  blood ;  for  in  them  the  friction  of  the  blood  is 
greatly  increased  by  the  enormous 
multiplication  of  the    surface   with 
which  it  is  brought  in  contact. 

At  the  circumference  of  the  stream 
in  the  larger  capillaries,  but  chiefly 
in  the  small  arteries  and  veins,  in 
contact  with  the  walls  of  the  vessel, 
and  adhering  to  them,  there  is  a 
layer  of  liquor  sanguinis  which  ap- 
pears to  be  motionless.  The  exist- 
ence   of    this    still    layer,    as    it    is 

1      •       •     e  i     i      ^i       f  j.i  rig.  140.—  i  (C.)    in  the  web 

termed,  is  inferred    both    from  the  the  nog's  foot  connecting  a 

,   p,  .,  ,  .    ,  small   artery    (A)   vrith  a  small 

general  fact  that  SUCh  an  one    exists  veinV   after  Allen  Thomson). 

in  all  fine  tubes  traversed  by  fluid, 

and  from  what  can  be  seen  in  watching  the  movements  of  the  blood- 
corpuscles.  The  red  corpuscles  occupy  the  middle  of  the  stream 
and  move  with  comparative  rapidity  ;  the  colourless  lymph-cor- 
puscles run  much  more  slowly  by  the  walls  of  the  vessel ;  while  next 
to  the  wall  there  is  often  a  transparent  space  in  which  the  fluid 
appears  to  be  at  rest ;  for  if  any  of  the  corpuscles  happen  to  be  forced 
within  it,  they  move  more  slowly  than  before,  rolling  lazily  along 
the  side  of  the  vessel,  and  often  adhering  to  its  wall.  Part  of  this 
slow  movement  of  the  pale  corpuscles  and  their  occasional  stoppage 
may  be  due  to  their  having  a  natural  tendency  to  adhere  to  the 
walls  of  the  vessels.  Sometimes,  indeed,  when  the  motion  of  the 
blood  is   not  strong,  many  of  the  white  corpi  'llect   in  a 

capillary  vessel,  and  for  a  time  entirely  prevent  the  passage  of  the 
red  corpuscles. 


CIRCULATION    OF    THE    BLOOD. 


[CHAP.  v. 


198 

Intermittent  flow  in  the  Capillaries.— When  the  peripheral 
resistance  is  greatly  diminished  by  the  dilatation  of  the  small 
arteries  and  capillaries,  so  much  blood  passes  on  from  the  arteries 
into  the  capillaries  at  each  stroke  of  the  heart,  that  there  is  not 
sufficient  remaining  in  the  arteries  to  distend  them.  Thus,  the 
intermittent  current  of  the  ventricular  systole  is  not  converted 
into  a  continuous  stream  by  the  elasticity  of  the  arteries  before 
the  capillaries  are  reached  ;  and  so  intermittency  of  the  flow  occurs 
in  capillaries  and  veins  and  a  pulse  is  produced.  The  same  phe- 
nomenon may  occur  when  the  arteries  become  rigid  from  disease, 
and  when  the  beat  of  the  heart  is  so  slow  or  so  feeble  that  the 
blood  at  each  cardiac  systole  has  time  to  pass  on  to  the  capillaries 
before  the  next  stroke  occurs,  the  amount  of  blood  sent  at  each 
stroke  bein^  insufficient  to  properly  distend  the  elastic  arteries. 

Diapedesis  of  Blood-Corpuscles. — Until  within  the  last  few 
years  it  has  been  generally  supposed  that  the  occurrence  of  any 

transudation  from  the  interior  of  the 
capillaries  into  the  midst  of  the  surround- 
ing tissues  was  confined,  in  the  absence  of 
injury,  strictly  to  the  fluid  part  of  the 
blood  ;  in  other  words,  that  the  corpuscles 
could  not  escape  from  the  circulating 
stream,  unless  the  wall  of  the  containing 
blood-vessel  were  ruptured.  It  is  true 
that  an  English  physiologist,  Augustus 
Waller,  affirmed,  in  1846,  that  he  had  seen 
blood-corpuscles,  both  red  and  white,  pass 
bodily  through  the  wall  of  the  capillary 
vessel  in  which  they  were  contained  (thus 
confirming  what  had  been  stated  a  short 
time  previously  by  Addison);  and  that, 
as  no  opening  could  be  seen  before  their 
escape,  so  none  could  be  observed  after- 
wards— so  rapidly  was  the  part  healed. 
But  these  observations  did  not  attract 
much  notice  until  the  phenomena  of  es- 
cape of  the  blood-corpuscles  from  the 
capillaries  and  minute  veins,  apart  from  mechanical  injury,  were 
re-discovered  by  Professor  Cohnheim  in  1867. 


mf&n 


Fig.  141. — A  large  capillary 
from  the  fro;/' 
eight  hours  after  irritation 
had  been  set  up,  showing 
emigration  of  leucocytes. 
a,  Cells  in  the  act  of  travers- 
ing the  capillary  wall ;  b, 
some  already  escaped. 

(Frey.) 


coup.  v.|  DIAPEDESIS. 


199 


Cohnheim's  experiment  demonstrating  the  passage  of  the  cor- 
puscles through  the  wall  of  the  blood-vessel,  is  performed  in  the 
following  manner.  A  frog  is  urarized,  that  is  to  say,  paralysis  is 
produced  by  injecting  under  the  skin  a  minute  quantity  of  the 
poison  called  urari  ;  and  the  abdomen  having  been  opened,  a 
portion  of  small  intestine  is  drawn  out,  and  its  transparent  mesen- 
tery spread  out  under  a  microscope.  After  a  variable  time,  occu- 
pied by  dilatation,  following  contraction  of  the  minute  vessels  and 
accompanying  quickening  of  the  blood-stream,  there  ensues  a  re- 
tardation  of  the  current,  and  blood-corpuscles,  both  red  and  white, 
begin  to  make  their  way  through  the  capillaries  and  small  veins. 

"Simultaneously  with  the  retardation  of  the  blood-stream,  the 
leucocytes,  instead  of  loitering  here  and  there  at  the  edge  ot 
the  axial  current,  begin  to  crowd  in  numbers  against  the  vascular 
wall.  In  this  way  the  vein  becomes  lined  with  a  continuous  pave- 
ment of  these  bodies,  which  remain  almost  motionless,  notwith- 
standing that  the  axial  current  sweeps  by  them  as  continuously 
as  before,  though  with  abated  velocity.  Now  is  the  moment 
at  which  the  eye  must  be  fixed  on  the  outer  contour  of  the 
vessel,  from  which,  here  and  there,  minute,  colourless,  button- 
shaped  elevations  spring,  just  as  if  they  were  produced  by  budding 
out  of  the  wall  of  the  vessel  itself.  The  buds  increase  gradually 
and  slowly  in  size,  until  each  assumes  the  form  of  a  hemispherical 
projection,  of  width  corresponding  to  that  of  the  leucocyte. 
Eventually  the  hemisphere  is  converted  into  a  pear-shaped  body, 
the  small  end  of  which  is  still  attached  to  the  surface  of  the  vein, 
while  the  round  part  projects  freely.  Gradually  the  little  mass  of 
protoplasm  removes  itself  further  and  further  away,  and,  as  it 
does  so,  begins  to  shoot  out  delicate  prongs  of  transparent  pro- 
toplasm from  its  surface,  in  nowise  differing  in  their  aspect 
from  the  slender  thread  by  which  it  is  still  moored  to  the  vessel. 
Finally  the  thread  is  severed  and  the  process  is  complete." 
(Burdon  Sanderson.) 

The  process  of  diapedesis  of  the  red  corpuscles,  which  occurs 
under  circumstances  of  impeded  venous  circulation,  and  conse- 
quently increased  blood-pressure,  resembles  closely  the  migration 
of  the  leucocytes,  with  the  exception  that  they  are  squeezed 
through  the  wall  of  the  vessel,  and  do  not,  like  them,  work  their 
way  through  by  amscboid  movement. 


200  CIRCULATION    OF    THE    BLOOD.  [chai\  v. 

Various  explanations  of  these  remarkable  phenomena  have  been 
suggested.  Some  believe  that  minute  openings  (stigmata  or 
pseudo-stomata)  between  contiguous  endothelial  cells  (p.  165)  pro- 
vide the  means  of  escape  for  the  blood-corpuscles.  But  the  chief 
share  in  the  process  is  to  be  found  in  the  vital  endowments  with 
respect  to  mobility  and  contraction  of  the  parts  concerned — both 
of  the  corpuscles  (Bastian)  and  the  capillary  wall  (Strieker). 
Burdon-Sanderson  remarks,  "the  capillary  is  not  a  dead  conduit, 
but  a  tube  of  living  protoplasm.  There  is  no  difficulty  in  under- 
standing how  the  membrane  may  open  to  allow  the  escape  of 
leucocytes,  and  close  again  after  they  have  passed  out ;  for  it  is 
one  of  the  most  striking  peculiarities  of  contractile  substance  that 
when  two  parts  of  the  same  mass  are  separated,  and  again  brought 
into  contact,  they  melt  together  as  if  they  had  not  been  severed." 

Hitherto,  the  escape  of  the  corpuscles  from  the  interior  of  the 
blood-vessels  into  the  surrounding  tissues  has  been  studied  chiefly 
in  connection  with  pathology.  But  it  is  impossible  to  say,  at  pre- 
sent, to  what  degree  the  discovery  may  not  influence  all  present 
notions  regarding  the  nutrition  of  the  tissues,  even  in  health. 

Vital  Capillary  Force. — The  circulation  through  the  capillaries 
must,  of  necessity,  be  largely  influenced  by  that  which  occurs  in 
the  vessels  on  either  side  of  them — in  the  arteries  or  the  veins  ; 
their  intermediate  position  causing  them  to  feel  at  once,  so  to 
speak,  any  alteration  in  the  size  or  rate  of  the  arterial  or  venous 
blood-stream.  Thus,  the  apparent  contraction  of  the  capillaries, 
on  the  application  of  certain  irritating  substances,  and  during  fear, 
and  their  dilatation  in  blushing,  may  be  referred  to  the  action  of 
the  small  arteries,  rather  than  to  that  of  the  capillaries  them- 
selves. But  largely  as  the  capillaries  are  influenced  by  these, 
and  by  the  conditions  of  the  parts  which  surround  and  support 
them,  their  own  endowments  must  not  be  disregarded.  They 
must  be  looked  upon,  not  as  mere  passive  channels  for  the  pas- 
sage of  blood,  but  as  possessing  endowments  of  their  own  (vital 
capillary  force),  in  relation  to  the  circulation.  The  capillary  wall 
is  actively  living  and  contractile  ;  and  there  is  no  reason  to  doubt 
that,  as  such,  it  must  have  an  important  influence  in  connection 
with  the  blood-current. 

Blood- Pressure    in   the   Capillaries. — From    observations 
upon  the  web  of  the  frog's  foot,  the  tongue  and  mesentery  of  the 


ohap.  v.]  CIBCULATION    l.\    THE    VEINS.  201 

frog,  the  tails  of  newts,  and  small  fishes  (Roy  and  Brown),  as  well 
as  upon  the  skin  of  t he  finger  behind  the  nail  (Kries),  by  careful 
estimation  of  the  amount  of  pressure  required  to  empty  the  vessels 
of  blood  under  various  conditions,  it  appears  that  the  blood- 
pressure  is  subject  to  variations  in  the  capillaries,  apparently 
following  the  variations  of  that  of  the  arteries;  and  that  up  to  -.< 
certain  point,  as  the  extra  vascular  pressure  is  increased,  so  docs 
the  pulse  in  the  arterioles,  capillaries,  and  venules  become  more 
and  more  evident.  The  pressure  in  the  first  case  (web  of  the 
frog's  foot)  lias  been  found  to  be  equal  to  about  14  to  20  mm.  of 
mercury  ;  in  other  experiments  to  be  equal  to  about  ±  to  |-  of  the 
ordinary  arterial  pressure. 

The    Circulation   in   the   Veins. 

The  blood-current  in  the  veins  is  maintained  by  the  slight 
vis  a  tergo  remaining  of  the  contraction  of  the  left  ventricle. 
Very  effectual  assistance,  however,  to  the  flow  of  blood  is  afforded 
by  the  action  of  the  muscles  capable  of  pressing  on  such  veins 
as  have  valves. 

The  effect  of  such  muscular  pressure  may  be  thus  explained. 
When  pressure  is  applied  to  any  part  of  a  vein,  and  the 
current  of  blood  in  it  is  obstructed,  the  portion  behind  the  seat 
of  pressure  becomes  swollen  and  distended  as  far  back  as  to  the 
next  pair  of  valves.  These,  acting  like  the  semilunar  valves  of  the 
heart,  and  being,  like  them,  inextensible  both  in  themselves  and 
at  their  margins  of  attachment,  do  not  follow  the  vein  in  its  dis- 
tension, but  are  drawn  out  towards  the  axis  of  the  canal.  Then, 
if  the  pressure  continues  on  the  vein,  the  compressed  blood,  tend- 
ing to  move  equally  in  all  directions,  presses  the  valves  down  into 
contact  at  their  free  edges,  and  they  close  the  vein  and  prevent 
regurgitation  of  the  blood.  Thus,  whatever  force  is  exercised  by 
the  pressure  of  the  muscles  on  the  veins,  is  distributed  partly  in 
pressing  the  blood  onwards  in  the  proper  course  of  the  circula- 
tion, and  partly  in  pressing  it  backwards  and  closing  the  valves 
behind  (fig.  128,  A  and  B). 

The  circulation  might  lose  as  much  as  it  gains  by  such 
compression  of  the  veins,  if  it  were  not  for  the  numerous  anasto- 
moses by  which  they  communicate,  one  with  another ;  for  through 


202  CIRCULATION    OF    THE    BLOOD.  [chap.  v. 

these,  the   closing   up  of  the  venous  channel   by  the  backward 

pressure  is  prevented  from  being  any  serious  hindrance  to  the 
circulation,  since  the  blood,  of  which  the  onward  course  is 
arrested  by  the  closed  valves,  can  at  once  pass  through  some 
anastomosing  channel,  and  proceed  on  its  way  by  another  vein. 
Thus,  therefore,  the  effect  of  muscular  pressure  upon  veins  which 
have  valves,  is  turned  almost  entirely  to  the  advantage  of  the 
circulation  ;  the  pressure  of  the  blood  onwards  is  all  advantageous, 
and  the  pressure  of  the  blood  backwards  is  prevented  from  being 
a  hindrance  by  the  closure  of  the  valves  and  the  anastomoses  of 
the  veins. 

The  effects  of  such  muscular  pressure  are  well  shown  by  the 
acceleration  of  the  stream  of  blood  when,  in  venesection,  the 
muscles  of  the  fore-arm  are  put  in  action,  and  by  the  general 
acceleration  of  the  circulation  during  active  exercise  :  and  the 
numerous  movements  which  are  continually  taking  place  in  the 
body  while  awake,  though  their  single  effects  may  be  less  striking, 
must  be  an  important  auxiliary  to  the  venous  circulation.  Yet 
they  are  not  essential ;  for  the  venous  circulation  continues  un- 
impaired in  parts  at  rest,  in  paralysed  limbs,  and  in  parts  in 
which  the  veins  are  not  subject  to  any  muscular  pressure. 

Rhythmical  Contraction  of  Veins. — In  the  web  of  the  bat's 
wing,  the  veins  are  furnished  with  valves,  and  possess  the  remark- 
able property  of  rhythmical  contraction  and  dilatation,  whereby 
the  current  of  blood  within  them  is  distinctly  accelerated. 
(Wharton  Jones.)  The  contraction  occurs,  on  an  average,  about 
ten  times  in  a  minute ;  the  existence  of  valves  preventing  regurgi- 
tation, the  entire  effect  of  the  contractions  was  auxiliary  to  the 
onward  current  of  blood.  Analogous  phenomena  have  been  fre- 
quently observed  in  other  animals. 

Blood-Pressure  in  the  Veins. — The  blood-pressure  gradu- 
ally falls  as  we  proceed  from  the  heart  to  the  arteries,  from  these 
to  the  capillaries,  and  thence  along  the  veins  to  the  right  auricle. 
The  blood-pressure  in  the  veins  is  nowhere  very  great,  but  is 
greatest  in  the  small  veins,  while  in  the  large  veins  towards  the 
heart  the  pressure  becomes  negative,  or,  in  other  words,  when  a 
vein  is  put  in  connection  with  a  mercurial  manometer  the  mercury 
will  fall  in  the  area  furthest  away  from  the  vein  and  will  rise  in 
the   area  nearest  the  vein,  having  a  tendency  to  suck  in  rather 


chap,  v.j  TELOCITY    OP    THE    I  Il:<  I'l.ATl  20^ 

than  t<>  push  forward.     In  the  reins  in  the  Deck  this  tend 
-uck  in  aii  cially  marked,  and  is  the  cane 

operations  in  that  region.  The  amount  of  pressure  in  the  brachial 
vein  is  said  to  Bupport  9  nun.  of  mercury,  whereas  the  pressure 
in  the  vein-  of  the  neck  is  about  equal  to  a  negative  pressure 
of  -  3  t<>  -  S  mm. 

The  variations  of  venous  pressure  during  le  and  diastole 

of  the  heart  are  very  Blight,  and  a  distinct  pulse  is  seldom  .seen  in 
vein-  I  under  very  extraordinary  circumstances. 

The  formidable  obstacle  to  the  upward  current  of  the  blood  in  the 
veins  of  the  trunk  and  extremities  in  the  erect  posture  supposed  to  be 
{•resented  by  the  gravitation  of  the  blood,  has  no  real  existence,  since 
the  pressure  exercised  by  the  column  of  blood  in  the  arteries,  will  be 
always  sufficient  to  support  a  column  of  venous  blood  of  the  same 
height  as  itself:  the  two  columns  mutually  balancing  each  other. 
Indeed,  so  l<>nu  as  both  arteries  and  veins  contain  continuous 
columns  of  blood,  the  force  of  gravitation,  whatever  be  the  position 
of  the  body,  can  have  no  power  to  move  or  resist  the  motion 
of  any  part  of  the  blood  in  any  direction.  The  lowest  blood- 
-  have,  of  course,  to  bear  the  greatest  amount  of  pressure; 
the  pressure  on  each  part  being  directly  proportionate  to  the 
height  of  the  column  of  blood   above  it  :  hence  their  liability  to 

tension.  But  this  pressure  bears  equally  on  both  arteries  and 
veins,  and  cannot  either  move,  or  resist  the  motion  of,  the  fluid 
they  contain,  so  long  as  the  columns  of  fluid  are  of  equal  height 
in  both,  and  continuous. 

Velocity  of  the  Circulation. 

The  velocity  of  the  blood-current  at  any  given  point  in  the 
various  divisions  of  the  circulatory  system  is  inversely  propor- 
tional to  their  sectional  area  at  that  point.  If  the  sectional  area 
of  all  the  branches  of  a  vessel  united  were  always  the  same  - 
that  of  the  vessel  from  which  they  arise,  and  if  the  aggregate 
sectional  area  of  the  capillary  vessels  were  equal  to  that  of  the 
aorta,  the  mean  rapidity  of  the  bkxxTs  motion  in  the  capillaries 
would  be  the  same  as  in  the  aorta  and  largest  arteries  :  and  if  a 
similar  correspondence  of  capacity  existed  in  the  veins  and  arteries, 
there  would  be  an  equal  correspondence  in  the  rapidity  of  the 
circulation  in  them.      But  the  arterial  and  venous  systems  may  be 


204 


CIRCULATION    OF    THE    BLOOD. 


[chap,  v. 


represented  by  two  truncated  cones  with  their  apices  directed 
towards  the  heart  ;  the  area  of  their  united  base  (the  sectional 
area  of  the  capillaries)  being  400 — 800  times  as  great  as  that  of 
the  truncated  apex  representing  the  aorta.  Thus  the  velocity  of 
blood  in  the  capillaries  is  at  least  —^  of  that  in  the  aorta. 

Velocity  in  the  Arteries.— The  velocity  of  the  stream  of  blood 
is  greater  in  the  arteries  than  in  any  other  part  of  the  circulatory 
system,  and  in  them  it  is  greatest  in  the  neighbourhood  of  the 
heart,  and  during  the  ventricular  systole  ;  the  rate  of  movement 
diminishing  during  the  diastole  of  the  ventricles,  and  in  the  parts 
of  the  arterial  system  most  distant  from  the  heart.  Chauveau 
has  estimated  the  rapidity  of  the  blood-stream  in  the  carotid  of 
the  horse  at  over  20  inches  per  second  during  the  heart's  systole, 
and  nearly  6  inches  during  the  diastole  (520 — 150  mm.). 

Estimation  of  the  Velocity. — Various  instruments  have  been  de- 
vised for  measuring  the  velocity  of  the  blood-stream  in  the  arteries. 
Ludwig's  " Stromvhr"  (fig.  142)  consists  of 
an  U-shaped  glass  tube  dilated  at  a  and  a', 
and  whose  extremities,  h  and  i,  are  of  known 
calibre.  The  bulbs  can  be  filled  by  a  common 
opening  at  k.  The  instrument  is  so  contrived 
that  at  b  and  b'  the  glass  part  is  firmly  fixed 
into  metal  cylinders,  which  are  fixed  into  a 
circular  horizontal  table,  c  c,  capable  of  hori- 
zontal movement  on  a  similar  table  d  d'  about 
the  vertical  axis  marked  in  figure  by  a  dotted 
line.  The  opening  in  c  c,  when  the  instru- 
ment is  in  position,  as  in  fig.,  corresponds 
exactly  with  those  in  d  d' ;  but  if  c  c'  be 
turned  at  right  angles  to  its  present  position, 
there  is  no  communication  between  h  and  a, 
and  i  and  a',  but  h  communicates  directly 
with  i  ;  and  if  turned  through  two  right 
angles  c'  communicates  with  d,  and  c  with  d', 
and  there  is  no  direct  connection  between  h 
and  i.  The  experiment  is  performed  in  the 
following  way  : — The  artery  to  be  experi- 
mented upon  is  divided  and  connected  with  two  cannulse  and 
tubes  which  fit  it    accurately  with  h   and   i — h  the  central  end, 


Fig.  142. — Ltidvrig's 
Stromuhr. 


(  HAT.  \ 


VELOCITY  IN  THE  ARTERIES. 


205 


and  i  the  peripheral  ;  the  bulb  a  is  filled  with  olive  oil  up  to 
a  point  rather  Lower  than  /■,  and  or' and  the  remainder  of  a  ua 
filled  with  defibrinated  blood  ;  the  tube  on  k  is  then  carefully 
olamped  \  the  tubes  d  and  ct  are  also  filled  with  defibrinated  blood. 
When  everything  is  ready,  the  blood  is  allowed  to  How  into  a 
through  //,  and  it  pushes  before  it  the  oil,  and  thai  the  defibrinated 
blood  into  the  artery  through  /,  and  replaces  it  in  a  ;  when  the 
blood  reaches  the  former  level  of  the  oil  in  a,  the  disc  c  c  is  turned 
rapidly  through  two  right  angles,  and  the  blood  flowing  through 
(I  into  a  again  displaces  the  oil  which  is  driven  into  a.  This  is 
repeated  Bevera]  times,  and  the  duration  of  the  experiment  noted. 
The  capacity  of  a  and  a!  is  known;  the  diameter  of  the  artery  is 
also  known  by  its  corresponding  with  the  cannulas  of  known  dia- 
meter, and  as  the  number  of  times  a  has  been  filled  in  a  given 
time  is  known,  the  velocity  of  the  current  can  be  calculated. 

Chauveau's  instrument  (fig.  143)  consists  of  a  thin   brass  tube, 
0,  in  one  side  of  which  is  a  small  perforation  closed  by  thin  vul- 


Fig.  143. — Diagram  of  Chauveau's  Instrument,  o.  Brass  tube  for  introduction  into  the 
lumen  of  the  artery,  and  containing'  an  index-needle,  which  passes  through  the  elastic 
membrane  in  its  side,  and  moves  by  the  impulse  of  the  blood-current,  c.  Graduated 
scale,  for  measuring  the  extent  of  the  oscillations  of  the  needle. 


canised  indiarubber.  Passing  through  the  rubber  is  a  tine  lever, 
one  end  of  which,  slightly  flattened,  extends  into  the  lumen  of  the 
tube,  while  the  other  moves  over  the  face  of  a  dial.  The  tube  is 
inserted  into  the  interior  of  an  artery,  and  ligatures  applied  to  fix 
it,  so  that  the  movement  of  the  blood  may,  in  flowing  through  the 
tube,  be  indicated  by  the  movement  of  the  outer  extremity  of  the 
lever  on  the  face  of  the  dial. 


206  CIRCULATION    OF    THE    BLOOD.  [chap.  v. 

The  Hcematochometer  of  Vierordt,  and  the  instrument  of  Lortet, 
resemble  in  principle  that  of  Chauveau. 

Velocity  in  the  Capillaries. — The  observations  of  Hales, 
E.  H.  Weber,  and  Valentin  agree  very  closely  as  to  the  rate  of  the 
blood-current  in  the  capillaries  of  the  frog ;  and  the  mean  of  their 
estimates  gives  the  velocity  of  the  systemic  capillary  circulation  at 
about  one  inch  (25  mm.)  per  minute.  The  velocity  in  the  capil- 
laries of  warm-blooded  animals  is  greater.  In  the  dog  ■£§  to  yj^ 
inch  (-5  to  75  nun.)  a  second.  This  may  seem  inconsistent  with 
the  facts  which  show  that  the  whole  circulation  is  accomplished 
in  about  half  a  minute.  But  the  whole  length  of  capillary  vessels, 
through  which  any  given  portion  of  blood  has  to  pass,  probably 
does  not  exceed  from  -^th  to  J^th  of  an  inch  (.5  mm.);  and 
therefore  the  time  required  for  each  quantity  of  blood  to  traverse 
its  own  appointed  portion  of  the  general  capillary  system  will 
scarcely  amount  to  a  second. 

Velocity  in  the  Veins. — The  velocity  of  the  blood  is  greater 
in  the  veins  than  in  the  capillaries,  but  less  than  in  the  arteries  : 
this  fact  depending  upon  the  relative  capacities  of  the  arterial  and 
venous  systems.  If  an  accurate  estimate  of  the  proportionate 
areas  of  arteries  and  the  veins  corresponding  to  them  could  be 
made,  we  might,  from  the  velocity  of  the  arterial  current,  calcu- 
late that  of  the  venous.  An  usual  estimate  is,  that  the  capacity 
of  the  veins  is  about  twice  or  three  times  us  great  as  that  of 
the  arteries,  and  that  the  velocity  of  the  blood's  motion  is,  there- 
fore, about  twice  or  three  times  as  great  in  the  arteries  as  in 
the  veins,  8  inches  (about  200  mm.)  a  second.  The  rate  at 
which  the  blood  moves  in  the  veins  gradually  increases  the  nearer 
it  approaches  the  heart,  for  the  sectional  area  of  the  venous 
trunks,  compared  with  that  of  the  branches  opening  into 
them,  becomes  gradually  less  as  the  trunks  advance  towards  the 
heart. 

Velocity  of  the  Circulation  as  a  whole. — It  would  appear 
that  a  portion  of  blood  can  traverse  the  entire  course  of  the  circu- 
lation, in  the  horse,  in  half  a  minute.  Of  course  it  would  require 
longer  to  traverse  the  vessels  of  the  most  distant  part  of  the 
extremities  than  to  go  through  those  of  the  neck  :  but  taking  an 
average  length  of  vessels  to  be  traversed,  and  assuming,  as  we  may, 
that  the  movement  of  blood  in  the  human  subject  is  not  slower 


chap.  v.|  VELOI  ITY    OF    THE    CIBCULATION.  207 

than  in  the  horse,  it  may  1"'  concluded  thai  half  ;t  minute  repi 
Benta  the.a^  ite. 

Satisfactory  data  for  these  estimates  are  afforded  by  the  results 
of  experiments   I       scertain  the  rapidity  with  which   ;  in- 

troduced into  the  blood  are  transmitted  from  one  part  >>i  the 
vascular  Bystem  to  another.  The  time  required  for  the  j 
of  a  solution  of  potassium  ferrocyanide,  mixed  with  the  blood, 
from  one  jugular  vein  (through  the  right  side  of  the  heart,  the 
pulmonary  vessels,  the  left  cavities  of  the  heart,  and  the 
general  circulation)  to  the  jugular  vein  of  the  opposite  Bide, 
varies  from  twenty  to  thirty  seconds.  The  same  Bubstance  was 
transmitted  from  the  jugular  vein  to  the  great  saphena  in  twenty 
seconds;  from  the  jugular  vein  to  the  masseteric  artery,  in 
between  fifteen  and  thirty  seconds ;  to  the  facial  artery,  in  one 
experiment,  in  between  ten  and  fifteen  seconds  ;  in  another  ex- 
periment in  between  twenty  and  twenty-five  seconds:  in  its  transit 
from  the  jugular  vein  to  the  metatarsal  artery,  it  occupied  between 
twenty  and  thirty  seconds,  and  in  one  instance  more  than  forty 
seconds.  The  result  was  nearly  the  same  whatever  was  the  rate 
of  the  heart's  action. 

In  all  these  experiments,  it  is  assumed  that  the  substance 
injected  moves  with  the  blood,  and  at  the  same  rate,  and 
does  not  move  from  one  part  of  the  organs  of  circulation  to 
another  by  diffusing  itself  through  the  blood  or  tissues  more 
quickly  than  the  blood  moves.  The  assumption  is  sufficiently 
probable,  to  be  considered  nearly  certain,  that  the  times  above 
mentioned,  as  occupied  in  the  passage  of  the  injected  substances, 
are  those  in  which  the  portion  of  blood,  into  which  each  was 
injected,  was  carried  from  one  part  to  another  of  the  vascular 
system. 

Another  mode  of  estimating  the  general  velocity  of  the  circu- 
lating blood,  is  by  calculating  it  from  the  quantity  of  blood 
supposed  to  be  contained  in  the  body,  and  from  the  quantity 
which  can  pass  through  the  heart  in  each  of  its  actions.  But 
the  conclusions  arrived  at  by  this  method  are  less  satisfactory. 
For  the  estimates  both  of  the  total  quantity  of  blood,  and  of  the 
capacity  of  the   cavities  of  the  heart,  hav<  t  only  approxi- 

mated to  the  truth.     Still  the  most  careful  of  the  estimates  thus 
made  accord  very  nearly  with  those  already  mentioned  ;  and  it 


208  CIRCULATION    OF    THE    BLOOD.  [chap.  v. 

may  be  assumed  that  the  blood  may  all  pass  through  the  heart  in 
from  twenty-five  to  fifty  seconds. 

Peculiarities  of  the  Circulation  in  Different  Parts.— 
The  most  remarkable  peculiarities  attending  the  circulation  of 
blood  through  different  organs  are  observed  in  the  cases  of  the 
brain,  the  erectile  organs,  the  lungs,  the  liver,  and  the  kidney. 

i.  In  the  Brain. — For  the  due  performance  of  its  functions, 
the  brain  requires  a  large  supply  of  blood.  This  object  is  effected 
through  the  number  and  size  of  its  arteries,  the  two  internal 
carotids,  and  the  two  vertebrals.  It  is  further  necessary  that  the 
force  with  which  this  blood  is  sent  to  the  brain  should  be  less,  or 
at  least  should  be  subject  to  less  variation  from  external  circum- 
stances than  it  is  in  other  parts,  and  so  the  large  arteries  are  very 
tortuous  and  anastomose  freely  in  the  circle  of  Willis,  which  thus 
insures  that  the  supply  of  blood  to  the  brain  is  uniform,  though 
it  may  by  an  accident  be  diminished,  or  in  some  way  changed, 
through  one  or  more  of  the  principal  arteries.  The  transit  of  the 
large  arteries  through  bone,  especially  the  carotid  canal  of  the 
temporal  bone,  may  prevent  any  undue  distension ;  and  uniformity 
of  supply  is  further  insured  by  the  arrangement  of  the  vessels  in 
the  pia  mater,  in  which,  previous  to  their  distribution  to  the  sub- 
stance of  the  brain,  the  large  arteries  break  up  and  divide  into 
innumerable  minute  branches  ending  in  capillaries,  which,  after 
frequent  communications  with  one  another,  enter  the  brain,  and 
cany  into  nearly  every  part  of  it  uniform  and  equable  streams  of 
blood.  The  arteries  are  also  enveloped  in  a  special  lymphatic 
sheath.  The  arrangement  of  the  veins  within  the  cranium  is  also 
peculiar.  The  large  venous  trunks  or  sinuses  are  formed  so  as  to 
be  scarcely  capable  of  change  of  size  ;  and  composed,  as  they  are,  of 
the  tough  tissue  of  the  dura  mater,  and,  in  some  instances,  bounded 
on  one  side  by  the  bony  cranium,  they  are  not  compressible  by 
any  force  which  the  fulness  of  the  arteries  might  exercise  through 
the  substance  of  the  brain ;  nor  do  they  admit  of  distension  when 
the  flow  of  venous  blood  from  the  brain  is  obstructed. 

The  general  uniformity  in  the  supply  of  blood  to  the  brain, 
which  is  thus  secured,  is  well  adapted,  not  only  to  its  functions, 
but  also  to  its  condition  as  a  mass  of  nearly  incompressible  sub- 
stance placed  in  a  cavity  with  unyielding  walls.  These  conditions 
of  the  brain  and  skull  have  appeared,  indeed,  to  some,  enough  to 


chap,  v.]        PECULIARITIES    OF    THE    CIRCl'I, ATIUX.  209 

justify  the  opinion  tliat  the  quantity  of  blood  in  the  bruin  must 
be  tit  all  times  the  same.  It  was  found  that  in  animals  bled  fco 
death,  without  any  aperture  being  made  in  the  cranium,  the  brain 
became  pale  and  anaemic  like  other  parts.  And  in  death  from 
strangling  or  drowning,  congestion  of  the  cerebral  vessels  ;  while 
in  death  by  pmssic  acid,  the  quantity  of  blood  in  the  cavity  of 
the  cranium  was  determined  by  the  position  in  which  the  animal 
was  placed  after  death,  the  cerebral  vessels  being  congested  when 
the  animal  was  suspended  with  its  head  downwards,  and  com- 
paratively empty  when  the  animal  was  kept  suspended  by  the 
ears.  That,  it  was  concluded,  although  the  total  volume  of  the 
contents  of  the  cranium  is  probably  nearly  always  the  same,  yet 
the  quantity  of  blood  in  it  is  liable  to  variation,  its  increase  or 
diminution  being  accompanied  by  a  simultaneous  diminution  or 
increase  in  the  quantity  of  the  cerebro-spinal  fluid,  which,  by 
readily  admitting  of  being  removed  from  one  part  of  the  brain 
and  spinal  cord  to  another,  and  of  being  rapidly  absorbed,  and  as 
readily  effused,  would  serve  as  a  kind  of  supplemental  fluid  to  the 
other  contents  of  the  cranium,  to  keep  it  uniformly  filled  in  case 
of  variations  in  their  quantity  (Burrows).  And  there  can  be  no 
doubt  that,  although  the  arrangements  of  the  blood-vessels,  to 
which  reference  has  been  made,  ensure  to  the  brain  an  amount  of 
blood  which  is  tolerably  uniform,  yet,  inasmuch  as  with  every 
beat  of  the  heart  and  every  act  of  respiration,  and  under  many 
other  circumstances,  the  quantity  of  blood  in  the  cavity  of  the 
cranium  is  constantly  varying,  it  is  plain  that,  were  there  not  pro- 
vision made  for  the  possible  displacement  of  some  of  the  contents 
of  the  unyielding  bony  case  in  which  the  brain  is  contained,  there 
would  be  often  alternations  of  excessive  pressure  with  insufficient 
supply  of  blood.  Hence  we  may  consider  that  the  cerebro-spinal 
fluid  in  the  interior  of  the  skull  not  only  subserves  the  mechanical 
functions  of  fat  in  other  parts  as  a  packing  material,  but  by  the 
readiness  with  which  it  can  be  displaced  into  the  spinal  canal, 
provides  the  means  whereby  undue  pressure  and  insufficient  supply 
of  blood  are  equally  prevented. 

Chemical  Composition  of  Cerebro-spinal  Fluid. — The  cerebro-spinal  fluid 
is  transparent,  colourless,  not  viscid,  with  a  saline  taste  and  alkaline  reaction, 
and  is  not  affected  by  heat  or  acids.  It  contains  981 — 984  parts  water, 
sodium  chloride,  traces  of   potassium  chloride,   of  sulphates,   carbonates, 

p 


2I0  CIRCULATION    OF    THE    BLOOD.  [chap.  v. 

alkaline  and  earthy  phosphates,  minute  traces  of  urea,  sugar,  sodium  lactate, 
fatty  matter,  cholesterin,  and  albumen  (Flint). 

2.  In  Erectile  Structures. — The  instances  of  greatest  variation 
in  the  quantity  of  blood  contained,  at  different  times,  in  the  same 
organs,  are  found  in  certain  structures  which,  under  ordinary  cir- 
cumstances, are  soft  and  flaccid,  but,  at  certain  times,  receive  an 
unusually  large  quantity  of  blood,  become  distended  and  swollen 
by  it,  and  pass  into  the  state  which  has  been  termed  erection. 
Such  structures  are  the  corpora  cavernosa  and  corpus  spongiosum 
of  the  penis  in  the  male,  and  the  clitoris  in  the  female ;  and,  to  a 
less  degree,  the  nipple  of  the  mammary  gland  in  both  sexes. 
The  corpus  cavemosum  penis,  which  is  the  best  example  of  an 
erectile  structure,  has  an  external  fibrous  membrane  or  sheath  ; 
and  from  the  inner  surface  of  the  latter  are  prolonged  numerous 
tine  lamellae  which  divide  its  cavity  into  small  compartments 
looking  like  cells  when  they  are  inflated.  Within  these  is 
situated  the  plexus  of  veins  upon  which  the  peculiar  erectile 
property  of  the  organ  mainly  depends.  It  consists  of  short  veins 
which  very  closely  interlace  and  anastomose  with  each  other  in  all 
directions,  and  admit  of  great  variation  of  size,  collapsing  in  the 
passive  state  of  the  organ,  but,  for  erection,  capable  of  an  amount 
of  dilatation  which  exceeds  beyond  comparison  that  of  the  arteries 
and  veins  which  convey  the  blood  to  and  from  them.  The 
strong  fibrous  tissue  lying  in  the  intervals  of  the  venous  plexuses, 
and  the  external  fibrous  membrane  or  sheath  with  which  it  is 
connected,  limit  the  distension  of  the  vessels,  and,  during  the 
state  of  erection,  give  to  the  penis  its  condition  of  tension  and 
firmness.  The  same  general  condition  of  vessels  exists  in  the 
corpus  spongiosum  urethras,  but  around  the  urethra  the  fibrous 
tissue  is  much  weaker  than  around  the  body  of  the  penis,  and 
around  the  glans  there  is  none.  The  venous  blood  is  returned 
from  the  plexuses  by  comparatively  small  veins  ;  those  from  the 
glans  and  the  fore  part  of  the  urethra  empty  themselves  into  the 
dorsal  veins  of  the  penis ;  those  from  the  cavemosum  pass  into 
deeper  veins  which  issue  from  the  corpora  cavernosa  at  the  crura 
penis  ;  and  those  from  the  rest  of  the  urethra  and  bulb  pass  more 
directly  into  the  plexus  of  the  veins  about  the  prostate.  For  all 
these  veins    one  condition  is  the  same;    namely,  that  they  are 


chap,  v.]       PECULLLRITIEfl    OF    THB  CIRCULATION.  2II 

liable  to  the  pres  f  muscles  when  the 3  "'  The 

ilea  chiefly  concerned  in  this  action  ai 

lerator   uriine.     Erection  results  from  the  distension  of  the 
as  plexuses  with  blood.     The  principal  exciting  cause  in  the 

erection  of  the  penis  is  nervous  irritation,  originating  in  the  part 
:.  or  derived  from  the  brain  and  spinal   cord.     The  nervous 

influence  is  communicated  to  the  penis  by  the  pudic  nerves,  which 
ramify  in  its  vascular  tissue  :  and  after  their  division  in  the  fa 
the  penis  is  no  longer  capable  of  erection. 

This  influx  of  the  blood  is  the  first  condition  necessary  for 
erection,  and  through  it  alone  much  enlargement  and  turgescence 
<»f  the  penis  may  ensue.  But  the  erection  is  probably  not  com- 
plete, nor  maintained  for  any  time  except  when,  together  with 
this  influx,  the  muscles  already  mentioned  contract,  and  by  1 

sing  the   veins,  stop    the    efflux   of  blood,  or  prevent  it  from 
being  as  great  as  the  influx. 

It  appears  to  be  only  the  most  perfect  kind  of  erection  that 
Is  the  help  of  muscles  to  compress  the  veins;  and  none  such 
can  materially  assist  the  erection  of  the  nipples,  or  that  amount 
of  turgescence,  just  Killing  short  of  erection,  of  which  the  spleen 
and  many  other  parts  are  capable.  For  such  turgescence  nothing 
more  seems  necessary  than  a  large  plexiform  arrangement  of  the 
veins,  and  such  arteries  as  may  admit,  upon  occasion,  augmented 
quantities  of  blood. 

(3,  4.  5).  The  circulation  vr>.  the  Lungs,  Liver,  and  Kidney*  will 
be  described  under  those  heads. 

Agents    concerned   in   the    circulation. — Before    quitting 
subject  it  will  be  as  well  to  bring  together  in  a  tabular  form 
the  various  agencies  concerned  in  maintaining  the  circulation. 

1.  The  Systole  and  Diastole  of  the  Heart,  the  former  pumping 
•     the  aorta  and  so  into  the  arterial  system  a  certain  amount  of 

:.  and  the  latter  to  some  extent  sucking  in  the  blood  from  the 
veins, 

2.  Tli-  elastic  and  muscular  coats  of  the  .  which  serve  to 
keep  up  an  equable  and  continuous  stream. 

3.  The  so-called  vital  capillary  force. 

4.  The    pressure  of  the   :  with  and  the 
:it  rhythmic  contraction  of  the  veins. 

5.  Aspiration  of  the  thorax  during  inspiration,  by  means  of  which 

p  2 


212  CIRCULATION    OF    THE    BLOOD.  [chap.  v. 

the  blood  is  drawn  from  the  large  veins  into  the  thorax  (to  he 
treated  of  in  next  Chapter). 

Discovery  of  the  Circulation. 

Up  to  nearly  the  close  of  the  sixteenth  century  it  "was  generally  believed 
that  the  blood  passed  from  one  ventricle  to  the  other  through  foramina  in 
the  "  septum  ventriculorum."  These  foramina  are  of  course  purely  imaginary, 
but  no  one  ventured  to  dispute  their  existence  till  Servetus  boldly  stated 
that  he  could  not  succeed  in  finding  them.  He  further  asserted  that  the 
blood  passed  from  the  Right  to  the  Left  side  of  the  heart  by  way  of  the 
lungs,  and  also  advanced  the  hypothesis  that  it  is  thus  "  revivified,"  re- 
marking that  the  Pulmonary  Artery  is  too  large  to  serve  merely  for  the 
nutrition  of  the  lungs  (a  theory  then  generally  accepted). 

Realdus,  Columbo,  and  Caesalpinus  added  several  important  observations. 
The  latter  showed  that  the  blood  is  slightly  cooled  by  passing  through  the 
lungs,  also  that  the  veins  swell  up  on  the  distal  side  of  a  ligature.  The 
existence  of  valves  in  the  veins  had  previously  been  discovered  by  Fabricius 
of  Aquapendente,  the  teacher  of  Harvey. 

The  honour  of  first  demonstrating  the  general  course  of  the  circulation 
belongs  by  right  to  Harvey,  who  made  his  grand  discovery  about  1618.  He 
was  the  first  to  establish  the  muscular  structure  of  the  heart,  which  had 
been  denied  by  many  of  his  predecessors  ;  and  by  careful  study  of  its  action 
both  in  the  body  and  when  excised,  ascertained  the  order  of  contraction  of 
its  cavities.  He  did  not  content  himself  with  inferences  from  the  anatomy 
of  the  parts,  but  employed  the  experimental  method  of  injection,  and  made 
an  extensive  and  accurate  series  of  observations  on  the  circulation  in  cold- 
blooded animals.  He  forced  water  through  the  Pulmonary  Artery  till  it 
trickled  out  through  the  Left  Ventricle,  the  tip  of  which  had  been  cut  off. 
Another  of  his  experiments  was  to  fill  the  Right  side  of  the  heart  with  water, 
tie  the  Pulmonary  Artery  and  the  Venas  Cavae  and  then  squeeze  the  Right 
ventricle  :  not  a  drop  could  be  forced  through  into  the  Left  ventricle,  and 
thus  he  conclusively  disproved  the  existence  of  foramina  in  the  septum 
ventriculorum.  "  I  have  sufficiently  proved,*'  says  he,  "  that  by  the  beating 
of  the  heart  the  blood  passes  from  the  veins  into  the  arteries  through  the 
ventricles,  and  is  distributed  over  the  whole  body.*' 

"  In  the  warmer  animals,  such  as  man,  the  blood  passes  from  the  Right 
Ventricle  of  the  Heart  through  the  Pulmonary  Artery  into  the  Lungs,  and 
thence  through  the  Pulmonary  Veins  into  the  Left  Auricle,  thence  into  the 
Left  Ventricle.'" 

Proofs  of  the  Circulation  of  the  Blood. — The  following  are 
the  main  arguments  by  which  Harvey  established  the  fact  of  the 
circulation  : — 

1.  The  heart  in  half  an  hour  propels  more  blood  than  the  whole 
mass  of  blood  in  the  body. 

2.  The  great  force  and  jetting  manner  with  which  the  blood 
spurts  from  an  opened  artery,  such  as  the  carotid,  with  every  beat 
of  the  heart. 


<hai\  v.]  TIIOOFS    OF    THE    CIRCULATION.  21 3 

3.  If  true,  the  normal  course  of  the  circulation  explains  why 
after  death  the  arteries  are  commonly  found  empty  and  the 
veins  full. 

4.  If  the  large  veins  near  the  heart  were  tied  in  a  fish  or  snake, 
the  heart  became  pale,  flaccid,  and  bloodless  ;  on  removing  the 
Ligature,  the  blood  again  flowed  into  the  heart.  If  the  artery  were 
tied,  the  heart  became  distended  ;  the  distension  lusting  until  the 
ligature  was  removed. 

5.  The  evidence  to  be  derived  from  a  ligature  round  a  limb.  If 
it  be  drawn  very  tight,  no  blood  can  enter  the  limb,  and  it  be- 
comes pale  and  cold.  If  the  ligature  be  somewhat  relaxed,  blood 
can  enter  but  cannot  leave  the  limb;  hence  it  becomes  swollen 
and  congested.  If  the  ligature  be  removed,  the  limb  soon  regains 
its  natural  appearance. 

6.  The  existence  of  valves  in  the  veins  which  only  permit  the 
blood  to  flow  towards  the  heart. 

7.  The  general  constitutional  disturbance  resulting  from  the 
introduction  of  a  poison  at  a  single  point,  e.  g.,  snake  poison. 

To  these  may  now  be  added  many  further  proofs  which  have 
iccumulated  since  the  time  of  Harvey,  e.  g. : — 

8.  Wounds  of  arteries  and  veins.  In  the  former  case  haemo- 
rrhage may  be  almost*  stopped  by  pressure  between  the  heart  and 
the  wound,  in  the  latter  by  pressure  beyond  the  seat  of  injury. 

9.  The  direct  observation  of  the  passage  of  blood  corpuscles 
from  small  arteries  through  capillaries  into  veins  in  all  transparent 
vascular  parts,  as  the  mesentery,  tongue  or  web  of  the  frog,  the 
tail  or  gills  of  a  tadpole,  ifcc. 

10.  The  results  of  injecting  certain  substances  into  the  blood. 
Further,  it  is  obvious  that  the  mere  fact  of  the  existence  of  a 

hollow  muscular  organ  (the  heart)  with  valves  so  arranged  as  to 
permit  the  blood  to  pass  only  in  one  direction,  of  itself  suggests 
the  course  of  the  circulation.  The  only  part  of  the  circulation 
which  Harvey  could  not  follow  is  that  through  the  capillaries,  for 
the  simple  reason  that  he  had  no  lenses  sufficiently  powerful  to 
enable  him  to  see  it.  Malpighi  (166 1)  and  Leeuwenhoek  (1668) 
demonstrated  it  in  the  tail  of  the  tadpole  and  lung  of  the  frog. 


2I4  RESPIRATION.  [chap.  vi. 


CHAPTER,    TI. 

RESPIRATION. 

The  maintenance  of  animal  life  necessitates  the  continual 
absorption  of  oxygen  and  excretion  of  carbonic  acid  ;  the  blood 
being,  in  all  animals  which  possess  a  well  developed  blood-vasculai 
system,  the  medium  by  which  these  gases  are  carried.  By  the 
blood,  oxygen  is  absorbed  from  without  and  conveyed  to  all  parts 
of  the  organism  ;  and,  by  the  blood,  carbonic  acid,  which  comes 
from  within,  is  carried  to  those  parts  by  which  it  may  escape 
from  the  body.  The  two  processes, — absorption  of  oxygen  and 
excretion  of  carbonic  acid, — are  complementary,  and  their  sum  is 
termed  the  process  of  Respiration. 

In  all  Vertebrata,  and  in  a  large  number  of  Invertebrata,  certain 
parts,  either  lungs  or  gills,  are  specially  constructed  for  bringing 
the  blood  into  proximity  with  the  aerating  medium  (atmospheric- 
air,  or  water  containing  air  in  solution).  In  some  of  the  lower 
Vertebrata  (frogs  and  other  naked  Amphibia)  the  skin  is  important 
as  a  respiratory  organ,  and  is  capable  of  supplementing,  to  some 
extent,  the  functions  of  the  proper  hreathing  apparatus ;  but  in  all 
the  higher  animals,  including  man,  the  respiratory  capacity  of  the 
skin  is  so  infinitesimal  that  it  may  be  practically  disregarded. 

Essentially,  a  lung  or  gill  is  constructed  of  a  fine  transparent 
membrane,  one  surface  of  which  is  exposed  to  the  air  or  waterr 
as  the  case  may  be,  while,  on  the  other,  is  a  network  of  blood- 
vessels,  the   only   separation   between  the   blood   and    aerating 

medium  being  the  thin  wall  of  the  blood-vessels,  and  the  fine 
membrane  on  one  side  of  which  vessels  are  distributed.  The 
difference  between  the  simplest  and  the  most  complicated  re- 
spiratory membrane  is  one  of  degree  only. 

The  various  complexity  of  the  respiratory  membrane,  and  the 
kind  of  aerating  medium,  are  not,  however,  the  only  conditions 
which  cause  a  difference  in  the  respiratory  capacity  of  different 
animals.  The  number  and  size  of  the  red  blood-corpuscles,  the 
mechanism  of  the  breathing  apparatus,  the  presence  or  absence  of 


ohap.  vi.]  THE    RESPIRATORY    TISSUES,  215 

a  pulmonary  heart,  physiologically  distinct  from  the  systemic,  are, 
all  of  them,  conditions  scarcely  second  in  importance. 

In  the  heart  of  man  and  all  Other  Mammalia,  the  right  ride  from  which 
the  blood  is  propelled  into  and  through  the  longs  may  he  termed  the  "  pul- 
monary "  heart  ;  while  the  left  side  La  "  systemic  "'  in  function.  In  many  of 
the  lower  animals.however.no  such  distinction  can  he  drawn.  Thus,  in 
Fish  the  heart  propels  the  blood  to  the  respiratory  organs  (gills)  ;  hut  there 
is  no  contractile  sac  corresponding  to  the  left  side  of  the  heart,  to  propel  the 
blood  directly  into  the  systemic  vessels. 

It  may  be  well  to  state  here  that  the  lungs  are  only  the 
me. limn  for  the  exchange,  on  the  part  of  the  blood,  of  carbonic 
acid  for  oxygen.  They  are  not  the  seat,  in  any  special  manner,  of 
those  combustion-processes  of  which  the  production  of  carbonic 
acid  is  the  final  result.  These  occur  in  all  parts  of  the  body — 
more  in  one  part,  less  in  another  :  chiefly  in  the  substance  of  the 
tissues,  but  in  part  in  the  capillary  blood-vessels  contained  in 
them. 

The  Respiratory  Passages  and  Tissues. 

The  object  of  respiration  is  the  interchange  of  gases  in  the 
lungs  ;  for  this  purpose  it  is  necessary  that  the  atmospheric  air 
shall  pass  into  them  and  be  expelled  from  them.  The  lungs  are 
contained  in  the  chest  or  thorax,  which  is  a  closed  cavity  having  no 
communication  with  the  outside,  except  by  means  of  the  respira- 
tory passages.  The  air  enters  these  passages  through  the  nostrils 
or  through  the  mouth,  thence  it  passes  through  the  larynx  into 
the  trachea  or  windpipe,  which  about  the  middle  of  the  chest 
divides  into  two  tubes,  bronchi,  one  to  each  (right  and  left) 
lung. 

The  Larynx  is  the  upper  part  of  the  passage  which  leads 
exclusively  to  the  lung  ;  it  is  formed  by  the  thyroid,  cricoid,  and 
arytenoid  cartilages  (fig.  145),  and  contains  the  vocal  cords,  by  the 
vibration  of  which  the  voice  is  chiefly  produced.  These  vocal 
cords  are  ligamentous  bands  attached  to  certain  cartilages  capable 
of  movement  by  muscles.  By  their  approximation  the  cords  can 
entirely  close  the  entrance  into  the  larynx ;  but  under  the  ordi- 
nary conditions,  the  entrance  of  the  larynx  is  formed  by  a 
more  or  less  triangular  chink  between  them,  called  the  rima 
(jlottidis.  Projecting  at  an  acute  angle  between  the  base  of  the 
tongue  and  the  larynx  to  which  it  is  attached,  is  a  leaf-shaped 


2l6 


RESPIRATION. 


[CHAP.  VI. 


cartilage,  with  its  larger  extremity  free,  called  the  epiglottis 
(fig.  145,  e).  The  whole  of  the  larynx  is  lined  by  mucous  mem- 
brane, which,  however,  is  extremely  thin  over  the  cords.     At  its 


■3 

*£*.■ 

I  • 

*^S*k 

^Lr            .  ilk 

—  Tongue 

•reap 

M-  ■■/, 

IM—ni, 

net  Glcttidi3 

Sftllincter  ~\?7je* 


Diahhrzuf 


Sfihittoter 
-AttC 


7rz\^ 


cTiV 


-  Diahhruci  m 


S/ihiticters 
yiheStinlder. 


Fig-  M4- 

lower  extremity  the  larynx  joins  the  trachea.*  With  the  exception 
of  the  epiglottis  and  the  so-called  cornicula  laryngis,  the  cartilages 
of  the  larynx  are  of  the  hyaline  variety. 

Structure  of  Epiglottis. — The  supporting  cartilage  is  com- 
posed of  yellow  elastic  cartilage,  enclosed  in  a  fibrous  sheath  (peri- 
chondrium), and  covered  on  both  sides  with  mucous  membrane. 


*  A  detailed  account  of  the  structure  and  function  of  the  Larynx  will  be 
found  in  Chapter  XVI. 


.  11.11".  \  I.J 


THE    LARYNX 


217 


^H 


The  anterior  surface,  which  looks  towards  the  base  of  the  tonj 
vlrmI  with  mucous  membrane,  the  basifl  of  which  is  fibrous 

elevated      towards 

both  .surfaces  in  the  form 
of  rudimentary  papilla?,  and 

oovered  with  Beveral  layers 
of  Bquamoufl  epithelium. 
Iu      it     ramify      capillary 

blood  -  vessels,  and  in  its 
meshes  are  a  large  number 
of  lymphatic  channels. 
Under  the  mucous  mem- 
brane, in  the  less  dense 
fibrous  tissue  of  which  it  is 
composed,  are  a  number  of 
tubular  glands.  The  pos- 
teriar  or  laryngeal  surface 
of  the  epiglottis  is  covered 
by  a  mucous  membrane, 
similar  in  structure  to  that 
on  the  other  surface,  but 
that  the  epithelial  coat  is 
thinner,  the  number  of 
strata  of  cells  being  less. 
and  the  papillae  few  and 
less  distinct.  The  fibrous 
tissue  which  constitutes  the 
mucous  membrane  is  in 
great  part  of  the  adenoid 
variety,  and  this  is  here 
and  there  collected  into 
distinct  masses  or  follicles. 
The  glands  of  the  posterior 
surface  are  smaller  but 
more  numerous  than  those 
<-n  the  other  surface.  In 
many    places    the    glands 

which  are   situated    nearest   to    the    perichondrium   are   directly 
continuous  through  apertures  in  the  cartilage  with  those  on  the 


Fig.  145. — Outline  wkowing  th*  general  form  of  the 
larynx,  trachea,  and  Iroic 

he  great  cornu  of  the  hyoid  bone  ;  e,  epi- 
glottis ;  t,  superior,  and  t' .  inferior  cornu  of 
the  thyroid  cartilage  ;  <\  middle  of  the  cricoid 
cartilage;  tr,  the  trachea,  showing  sixteen 
cartilaginous  rings ;  b,  the  right,  and  b',  the 
left  bronchus.     .Alien  Thomson.)     x  £. 


218 


liESPIRATIOX. 


[chap.  yi. 


other  side,  and  often  the  ducts  of  the  glands  from  one  side  of  the 
cartilage  pass  through  and  open  on  the  mucous  surface  of  the 


<^ 


other  side.  Taste  yoblets 
have  been  found  in  the 
epithelium  of  the  posterior 
surface  of  the  epiglottis, 
and  in  several  other 
situations  in  the  larvn^eal 
mucous  membrane. 

The  Trachea  and 
Bronchial  Tubes. — The 
trachea  or  wind -pipe  ex- 
tends from  the  cricoid  car- 
tilage, which  is  on  a  level 
with  the  fifth  cervical  ver- 
tebra, to  a  point  opposite 
the  third  dorsal  vertebra, 
where  it  divides  into  the 
two  bronchi,  one  for  each 
lung  (fig.  146).  It  mea- 
sures, on  an  average,  four 
or  four-and-a-half  inches  in 
length,  and  from  three- 
quarters  of  an  inch  to  an 
inch  in  diameter. 

Structure. — The  trachea 
is  essentially  a  tube  of 
fibro  -  elastic  membrane, 
within  the  layers  of  which 
are  enclosed  a  series  of 
Fig.  146.— Outi;  m  of  the    cartilaginous     rings,    from 

larynx,  trachea,  and  hronrlii  as  s?en  from  behind. 

/-.great  cornu  of  the  hyoid  bone;  t,  superior,  Sixteen    to    twenty  111   Ulim- 

and  t',  the  inferior  cornu  of  the  thvroid  card-  ,                rp,                .                           , 

lage  ;  e,  the  epiglottis ;  a,  points  to  the  back  of  Der.         1  liese     rings     extend 

both  the  arvtenoid  cartilages,  which  are  sur-  -,                     ,      ,        „                    , 

mounted  by 'the  cornicula  ;  c,  the  middle  rid<?e  Only  around   the  front    and 

on  the  back  of  the  cricoid  cartilage;  tr,  the  ajj--  _p  +i,fl  1        v>        /   1        + 

posterior  membranous  part  of  the  trachea  ;  h. ',' ,  SICieS  01    Hie  tracnea  ^aOOUt 

right  and  left  bronchi.     ( Allen  Thomson.)     *.  tWO-thirds  of  its  cirCUmfer- 

ence),  and  are  deficient  behind  ;  the  interval  between  their  poste- 
rior extremities  being  bridged  over  by  a  continuation  of  the 
fibrous  membrane  in  which  they  are  enclosed  (fig.   145).      The 


C1I.U'.    VI.] 


THE    TRAHIKA. 


219 


cartilages  of  the  trachea  and  bronchial  tubes  arc  of  th<    hy 
variety. 

Immediately  within  this  tube,  at  the  back,  is  a  layer  of  unstriped 
muscular  fibres,  which  extends,  transverse///.  1  ■•  -  .         the  end 
the  cartilaginous  rings  to  which  they  are  attached,  and  op] 
the  intervals  between  them,  also  ;  their  evident  function  being  I 


-  . 


:-- ; 


.  7 


yf.—i  .     o.  columnar  ciliated  epithelium  ;  b  and  <-,  proper  structure  of 

the  mucous  membrane,  containing  elastic  fibres  cut  across  trans'*.  -  .bmucou.-^ 

tissue  containing  mucous  glands,  e,  separated  from  the  hyaline  cartilage,  .7,  by  a 
fine  tibruus  tissue,  f\  /(.external investment  of  fine  fibrous  tissue.  (S.  K.  Alcock.) 

diminish,  when  required,  the  calibre  of  the  trachea  by  appi 
mating  the  ends  of  the  cartilages.     Outside  these  are  a  few  V 
tudiiwl  bundles  of  muscular  tissue,  which,  like  the  preceding,  arc 
attached  both  to  the  fibrous  and  cartilaginous  framework. 

The    mucous   membrane         aists  of  adenoid   tissue,   separate] 


220  EESPIEATIOX.  [cha*.  vi. 

from  the  stratified  columnar  epithelium  which  lines  it  by  a  homo- 
geneous basement  membrane.  This  is  penetrated  here  and  there 
by  channels  which  connect  the  adenoid  tissue  of  the  imccosa  with 
the  intercellular  substance  of  the  epithelium.  The  stratified 
columnar  epithelium  is  formed  of  several  layers  of  cells  (fig.  147), 
of  which  the  most  superficial  layer  is  ciliated,  and  is  often  branched 
downwards  to  join  connective-tissue  corpuscles  ;  while  between 
these  branched  cells  are  smaller  elongated  cells  prolonged  up 
towards  the  surface  and  down  to  the  basement  membrane.  Be- 
neath these  are  one  or  more  layers  of  more  irregularly  shaped 
cells.  In  the  deeper  part  of  the  mucosa  are  many  elastic  fibres 
between  which  lie  connective-tissue  corpuscles  and  capillary  blood- 
vessels. 

Numerous  mucous  glands  are  situate  on  the  exterior  and  in  the 
substance  of  the  fibrous  framework  of  the  trachea ;  their  ducts 
perforating  the  various  structures  which  form  the  wall  of  the 
trachea,  and  opening  through  the  mucous  membrane  into  the 
interior. 

The  two  bronchi  into  which  the  trachea  divides,  of  which  the 
right  is  shorter,  broader,  and  more  horizontal  than  the  left 
(fig.  145),  resemble  the  trachea  exactly  in  structure,  and  in  the 
arrangement  of  their  cartilaginous  rings.  On  entering  the  sub- 
stance of  the  lungs,  however,  the  rings,  although  they  still  form 
only  larger  or  smaller  segments  of  a  circle,  are  no  longer  confined 
to  the  front  and  sides  of  the  tubes,  but  are  distributed  impartially 
to  all  parts  of  their  circumference. 

The  bronchi  divide  and  sub-divide,  in  the  substance  of  the 
lungs,  into  a  number  of  smaller  and  smaller  branches,  which 
penetrate  into  every  part  of  the  organ,  until  at  length  they  end 
in  the  smaller  sub-divisions  of  the  lungs,  called  lobules. 

All  the  larger  branches  still  have  walls  formed  of  tough  mem- 
brane, containing  portions  of  cartilaginous  rings,  by  which  they 
are  held  open,  and  unstriped  muscular  fibres,  as  well  as  longi- 
tudinal bundles  of  elastic  tissue.  They  are  lined  by  mucous  mem- 
brane, the  surface  of  which,  like  that  of  the  larynx  and  trachea,  is 
covered  with  ciliated  epithelium  (fig.  148).  The  mucous  mem- 
brane is  abundantly  provided  with  mucous  glands. 

As  the  bronchi  become  smaller  and  smaller,  and  their  walls 
thinner,  the  cartilaginous  rings  become  scarcer  and  more  irregular, 


CHAP.  VI.  | 


THE    LUNGS. 


221 


until,  in  the  smaller  bronchia]  tubes,  they  arc  represented  only  by 
minute  and  scattered  cartilaginous  flakes.  And  when  the  bronchi,  1>\ 
successive  branches  are  reduced  to  about  -Jti  of  an  inch  in  diameter. 
they  lose  their  cartilaginous  element  altogether,  and  their  walls 
are  formed  only  of  a  tough  fibrous  clastic  membrane,  with  circular 
muscular  fibres  ;  they  are  still  lined,  however,  by  a  thin  mucous 


T7K 


Fig.  148. —  Transverse  section  of  a  bronchus,  about  \  inch  in  diameter,  e.  Epithelium 
(ciliated)  ;  immediately  beneath  it  is  the  mucous  membrane  or  internal  fibrous  layer, 
of  varying  thickness  ;  m,  muscular  layer  ;  s,  m,  submucous  tissue  ;  /',  fibrous  tissue  • 
r,  cartilage  enclosed  within  the  layer's  of  fibrous  tissue ;  g,  mucous  gland.  (F.  e! 
Schulze.) 

membrane,  with  ciliated  epithelium,  the  length  of  the  cells 
bearing  the  cilia  having  become  so  far  diminished,  that  the  cells 
are  now  almost  cubical.  In  the  smaller  bronchi  the  circular  mus- 
cular fibres  are  more  abundant  than  in  the  trachea  and  larger 
bronchi,  and  form  a  distinct  circular  coat. 

The  Lungs  and  Pleura. — The  Lungs  occupy  the  greater  por- 
tion of  the  thorax.  They  are  of  a  spongy  elastic  texture,  and  on 
section  appear  to  the  naked  eye  as  if  they  "were  in  great  part  solid 
organs,  except  here  and  there,  at  certain  points,  where  branches 
of  the  bronchi  or  air-tubes  may  have  been  cut  across,  and  show, 
on  the  surface  of  the  section,  their  tubular  structure.  In  fact, 
however,  the  lungs  are  hollow  organs,  each  of  which  communicates 
by  a  separate  orifice  with  a  common  air-tube,  the  trachea. 

The  Pleura, — Each  lung  is  enveloped  by  a  serous  membrane — the 
pleura,  one  layer  of  which  adheres  closely  to  the  surface  of  the  lung, 
and  provides  it  with  its  smooth  and  slippery  covering,  while  the 
other  adheres  to  the  inner  surface  of  the  chest-wall.  The  continuity 
of  the  two  layers,  which  form  a  closed  sac,  as  in  the  case  of  other 


222 


RESPIRATION. 


[chap.  VI. 


serous  membranes,  will  be  best  understood  by  reference  to  fig.  149. 
The  appearance  of  a  space,  however,  between  the  pleura  which 
covers  the  lung  {visceral  layer),  and  that  which  lines  the  inner  sur- 
face of  the  chest  {parietal  layer),  is  inserted  in  the  drawing  only 
for  the  sake  of  distinctness.  These  layers  are,  in  health,  every- 
where in  contact,  one  with  the  other ;  and  between  them  is  only 
just  so  much  fluid  as  will  ensure  the  lungs  gliding  easily,  in  their 


,  «,, .  J>ericairZium~      -, 

PuJhrtVttn  t  ••-"-  Pulm1 


Pulm^Veirv 


Left  Lung 


CEsojiliagul 


BrencJw.s 


Pig".  149. — Transverse  section  of  the  chest  (after  Gray). 

expansion  and  contraction,  on  the  inner  surface  of  the  parietal 
layer,  which  lines  the  chest-wall.  "While  considering  the  subject 
of  normal  respiration,  we  may  discard  altogether  the  notion  of  the 
existence  of  any  space  or  cavity  between  the  lungs  and  the  wall  of 
the  chest. 

If,  however,  an  opening  be  made  so  as  to  permit  air  or  fluid  to 
enter  the  pleural  sac,  the  lung,  in  virtue  of  its  elasticity,  recoils, 
and  a  considerable  space  is  left  between  the  lung  and  the  chest- 
wall.  In  other  words,  the  natural  elasticity  of  the  lungs  would 
cause  them  at  all  times  to  contract  away  from  the  ribs,  were  it  not 
that  the  contraction  is  resisted  by  atmospheric  pressure  which 
bears  only  on  the  inner  surface  of  the  air-tubes  and  air-cells.  On 
the  admission  of  air  into  the  pleural  sac,  atmospheric  pressure 
bears  alike  on  the  inner  and  outer  surfaces  of  the  lung,  and  their 
elastic  recoil  is  thus  no  longer  prevented. 

Structure  of  the  Pleura  and  Lung. — The  pulmonary  pleura  con- 
sists of  an  outer  or  denser  layer  and  an  inner  looser  tissue.  The 
former  or  'pleura  proper  consists  of  dense  fibrous  tissue  with  elastic 


<  HAW    VI 


'J  HE    LUNGS. 


223 


vered  l>\  endothelium,  the  cells  <>f  which  are  largi .  flat,  hya- 
line,  and  transparent  when  the  lung  is  expanded,  bul  become  smaller, 
thicker,  and  granular  when  the  lung  collapses.  In  the  pleura  is 
a  lymph-canalicular  system;  and  connective  tissue  corpus 
are  found  in  the  fibres  and  tissue  which  forms  its  groundwork. 
The  inner,  looser,  or  subpleura]  tissue  contains  lamellae  of  fibrous 
connective  tissue  and  connective  tiss  b  between  them. 

Numerous  lymphatics  are  to  l»e  met  with,  which  form  a  dense 
plexus  1  •  -.  many  of  which  contain  valve-.     They  are  simple 

endothelial  tubes,  and  take  origin  ill  the  lymph-canalicular  BJ 
of  the  pleura  proper.  Scattered  bundles  of  unstriped  muscular 
nr  in  the  pulmonary  pleura.  They  are  especially  strongly 
developed  on  those  parts  (anterior  and  internal  surfaces  of  lungs) 
which  move  most  freely  in  respiration:  their  function  is  doubt- 
n  to  aid  in  expiration.  The  structure  of  the  parietal  portion 
of  the  pleura  is  very  similar  to  that  of  the  visceral  layer. 

Each  lung  is  partially  subdivided  into  separate  portions  called 

a;  the  right  lung  into  three 
lobes,  and  the  left  into  two. 
Each  of  these  lobes,  again,  is 
composed  of  a   large   num- 
ber of  minute  parts,   called 
lobules.       Each    pulmonary 
lobule  may  be  considered  a 
lung  in  miniature,  consist- 
-   it  does,  of  a  branch 
of   the    bronchial    tub', 
air-cells,       blood       vess 
nerves,  and  lymphatics,  with 
a  sparing  amount  of  areolar 
le. 

On  entering  a  lobule,  the 
small  bronchial  tube,  the 
structure  of  which  has  been 

just  described  (a,  fig.  150),  divides  and  sub-divides;  its  walls 
at  the  same  time  becoming  thinner  and  thinner,  until  at 
length  thev  are  formed  only  of  a  thin  membrane  of  areolar  and 
elastic  tissue,  lined  by  a  layer  of  squamous  epithelium,  not  pro- 
vided with  cilia.     At   the  same  time,  they  are   altered  in  shape  : 


Fig.  150. —  Ciliary  epithelium  of  the  human  I 

<7,  Layer  of  longitudinally  arranged  elastic 
fibres ";  b,  basement  membrane ;  <-,  deepest 
cells,  circular  in  form  ;  d,  intermediate  elon- 
gated cells  ;  e,  outermost  layer  of  cells  fully 
developed  and  bearing  cilia.     X  350. 

::ker.; 


224 


RESPIRATION. 


[CHAP.  VI. 


Fig.  151. — Terminal  branch  of  a  bronchial  tube, 
with  its  infundibula  and  air-cells,  from  the 
margin  of  the  lung  of  a  monkey,  injected 
with  quicksilver,  a,  terminal  bronchial 
twig;  b  b,  infundibula  and  air-cells, 
x  10.     (F.  E.  Schuke.) 


each  of  the  minute  terminal  branches  -widening  out  funnel-wise, 
and  its  walls  being  pouched   out  irregularly  into  small  saccular 

dilatations,  called  air-cells  (fig. 
151,  b).  Such  a  funnel-shaped 
terminal  branch  of  the  bron- 
chial tube,  with  its  group  of 
pouches  or  air-cells,  has  been 
called  an  infundihulum  (figs. 
151,  152),  and  the  irregular 
oblong  space  in  its  centre, 
with  which  the  air-cells  com- 
municate, an  intercellular  pas- 
sage. 

The  air-cells,  or  air-vesicles, 
may  be  placed  singly,  like  re- 
cesses   from   the   intercellular 
passage,  but  more  often  they 
are  arranged  in  groups  or  even  in  rows,  like  minute  sacculated 
tubes  ;  so  that  a  short  series  of  vesicles,  all  communicating  with 

one  another,  open  by  a  common 
orifice  into  the  tube.  The  vesi- 
cles are  of  various  forms,  accord- 
ing to  the  mutual  pressure  to 
which  they  are  subject;  their 
walls  are  nearly  in  contact,  and 
they  vary  from  ■£§  to  ^  of  an 
inch  in  diameter.  Their  walls 
are  formed  of  fine  membrane, 
similar  to  that  of  the  intercellular 
passages,  and  continuous  with  it, 
which  membrane  is  folded  on 
itself  so  as  to  form  a  sharp-edged 
border  at  each  circular  orifice  of 
communication  between  contigu- 
ous air-vesicles,  or  between  the 
vesicles  and  the  bronchial  pas- 
sages. Numerous  fibres  of  elastic 
tissue  are  spread  out  between  contiguous  air-cells,  and  many  of 
these  are  attached  to  the  outer  surface  of  the  fine  membrane  of 


Fig.  152. — Two  small  infundibula  or  groups 
of  air-cells,  a  a,  with  air-cells,  b  b, 
and  the  ultimate  bronchial  tubes,  c  c, 
with  which  the  air-cells  communicate. 
From  a  new-bom  child.     (Kolliker.) 


I   MAP.    \  I.  | 


THE    LUNGS, 


22 


which  each  cell  is  composed,  imparting  to  it  additional  strength,  and 
the  power  of  recoil  after  distension.  The  cells  are  lined  by  a  layer 
of  epithelium  (fig.  153),  not  provided  with  cilia.  Outside  the 
cells,  ;i  network  of  pulmonary  capillaries  is  spread  out  so  denseli 
(fig.  1 54),  that  the  interspaces  or  meshes  arc  even  narrower  than  the 
vessels,  which  arc,  on  an  average,  .;,,',,,,  <>f  an   inch  iii  diameter. 


a  ■ 


Fig.  153. — From  a  section  of  lung  of  «  cat,  stained  with  silver  nitrate.  A.  D.  Alveolar  duct  or 
intercellular  passage.  S.  Alveolar  septa.  N.  Alveoli  or  air-cells,  lined  with  large  flat, 
nucleated  cells,  with  some  smaller  polyhedral  nucleated  cells.  Circular  muscular  fibres 
are  seen  surrounding  the  interior  of  the  alveolar  duct,  and  at  one  part  is  seen  a  group 
of  small  polyhedral  cells  continued  from  the  bronchus.     (Klein  and  Noble  Smith.) 


Between  the  atmospheric  air  in  the  cells  and  the  blood  in  these 
vessels,  nothing  intervenes  but  the  thin  walls  of  the  cells  and 
capillaries  :  and  the  exposure  of  the  blood  to  the  air  is  the  more 
complete,  because  the  folds  of  membrane  between  contiguous  cells, 
and  often  the  spaces  between  the  walls  of  the  same,  contain  only 
a  single  layer  of  capillaries,  both  sides  of  which  are  thus  at  once 
exposed  to  the  air. 

The  air-vesicles  situated  nearest  to  the  centre  of  the  lung  are 
smaller  and  their  networks  of  capillaries  are   closer  than  those 

Q 


226 


RESPIRATION. 


[CHAP.   VI. 


nearer  to  the  circumference.  The  vesicles  of  adjacent  lobules 
do  not  communicate  ;  and  those  of  the  same  lobule  or  proceeding 
from  the  same  intercellular  passage,  do  so  as  a  general  rule  only 
near  angles  of  bifurcation  ;  so  that,  when  any  bronchial  tube  is 
closed  or  obstructed,  the  supply  of  air  is  lost  for  all  the  cells 
opening  into  it  or  its  branches. 

Blood-supply, — The  lungs  receive  blood  from  two  sources,  (a) 
the  pulmonary  artery,  (6)  the  bronchial  arteries.  The  former 
conveys  venous  blood  to  the  lungs  for  its  arterial  nation,  and  this 


Fis 


1=4. — Capillary   net-ivork  of  Vie  pulmm  •--   '&  in  the  human  lung.      x  60. 

(Kolliker.) 


blood  takes  no  share  in  the  nutrition  of  the  pulmonary  tissues 
through  which  it  passes.  (b)  The  branches  of  the  bronchial 
arteries  ramify  for  nutrition's  sake  in  the  walls  of  the  bronchi,  of 
the  larger  pulmonary  vessels,  in  the  interlobular  connective  tissue, 
&c. ;  the  blood  of  the  bronchial  vessels  being  returned  chiefly 
through  the  bronchial  and  partly  through  the  pulmonary  veins. 

Lymphatics. — The  lymphatics  are  arranged  in  three  sets  :  — 
1.  Irregular  lacunaB  in  the  walls  of  the  alveoli  or  air-cells.  The 
lymphatic  vessels  which  lead  from  these  accompany  the  pulmonary 
vessels  towards  the  root  of  the  lung.  2.  Irregular  anastomosing 
spaces  in  the  walls  of  the  bronchi.  3.  Lymph-spaces  in  the 
pulmonary  pleura.     The  lymphatic  vessels  from  all  these  irregular 


chap,  v!.]  INSPIRATION.  227 

sinuses  pass  in  towards  the  root  of  the  lung  to  reaol    'in  bronchial 
glands. 

.v  .  -The  nerves  of  tlic  lung  arc  to  be  traced  from  the 
anterior  and  posterior  pulmonary  plexuses,  which  are  formed  by 
branches  of  the  vagus  and  sympathetic.  The  nerve*  follow  the 
course  of  the  vessels  and  bronchi,  and  in  the  walls  of*  the  latter 
many  small  ganglia  arc  situated. 

Mechanism  of  Respiration. 

Respiration  consists  of  the  alternate  expansion  and  contraction 
of  the  thorax,  by  means  of  which  air  is  drawn  into  or  expelled 
from  the  lungs.  These  acts  arc  called  Inspiration  and 
Expiration  respectively. 

For  the  inspiration  of  air  into  the  lungs  it  is  •  vident  that  all 
that  is  necessary  is  such  a  movement  of  the  side-walls  or  floor  of 
the  chest,  or  of  both,  that  the  capacity  of  the  interior  shall  be 
enlarged.  By  such  increase  of  capacity  there  will  be  of  course  a 
diminution  of  the  pressure  of  the  air  in  the  lungs,  and  a  fresh 
quantity  will  enter  through  the  larynx  and  trachea  to  equalise  the 
pressure  on  the  inside  and  outside  of  the  chest. 

For  the  expiration  of  air,  on  the  other  hand,  it  1-  also  evident 
that,  by  an  opposite  movement  which  shall  diminish  the  capacity  of 
the  chest,  the  pressure  in  the  interior  will  be  increased,  and  air 
will  be  expelled,  until  the  pressures  within  and  without  the  chest 
arc  again  equal  It  both  cases  the  air  passes  through  the  trachea 
and  larynx,  whether  in  entering  or  leaving  the  lungs,  there  being 
no  other  communication  with  the  exterior  of  the  body ;  and  the 
lung,  for  the  same  reason,  remains  under  all  the  circumstances 
described  closely  in  contact  with  the  walls  and  floor  of  the  chest. 
To  speak  of  expansion  of  the  chest,  is  to  speak  also  of  expansion 
of  the  lung. 

We  have  now  to  consider  the  means  by  which  the  respiratory 
movements  are  effected. 

Respiratory  Movements. 
A.  Inspiration. — The  enlargement  of  the  chest  in  inspiration 
is  a  muscular  act;  the  effect   of  the  action  of  the  inspiratory 
muscles  being  an  increase  in  the  size  of  the  chest-cavity  (a)  in  the 

Q  2 


228 


RESPIRATION. 


[CHAP.  VI. 


vertical,  and  (b)  in  the  lateral  and  antero-posterior  diameters.. 
The  muscles  engaged  in  ordinary  inspiration  are  the  diaphragm  ; 
the  external  intercostals  ;  parts  of  the  internal  intercostals  ;  the 
levatores  costarum;  and  serratus  posticus  superior. 

(a.)  The  vertical  diameter  of  the  chest  is  increased  by  the  con- 
traction and  consequent  descent  of  the  diaphragm, — the  sides  of 
the  muscle  descending  most,  and  the  central  tendon  remaining, 
comparatively  unmoved  ;  while  the  intercostal  and  other  muscles, 
by  acting  at  the  same  time,  prevent  the  diaphragm,  during  its 
contraction,  from  drawing  in  the  sides  of  the  chest. 

(b.)  The  increase  in  the  lateral  and  antero-posterior  diameters  of 
the  chest  is  effected  by  the  raising  of  the  ribs,  the  greater  number 


Fig.  155. — Diagram  of  axes  of  movement  of  ribs. 


of  which  are  attached  very  obliquely  to  the  spine  and  sternum  (see 
Figure  of  Skeleton  in  frontispiece). 

The  elevation  of  the  ribs  takes  place  both  in  front  and  at  the 
sides — the  hinder  ends  being  prevented  from  performing  any  up- 
ward movement  by  their  attachment  to  the  spine.  The  movement 
of  the  front  extremities  of  the  ribs  is  of  necessity  accompanied  by 
an  upward  and  forward  movement  of  the  sternum  to  which  they 


OH  \r.  VI.] 


INSINUATION. 


229 


are  attached,  the  movement  being  greater  at  the  lower  end  than  at 
the  upper  end  of  the  latter  bone. 

Th>  axes  of  rotation  in  these  movements  are  twoj  one  cor- 
responding with  a  line  drawn  through  the  two  articulations 
which  the  rib  forms  with  the  spine  (a  b,  fig.  155) ;  and  the  other, 
with  a  line  drawn  from  one  of  these  (head  of  rib)  to  the  sternum 
(A  B,  fig.  155,  and  fig.  156);  the  motion  of  the  rib  around  the 
latter  axis  being  somewhat  after  the  fashion  of  raising  the  handle 
of  a  bucket. 

The  elevation  of  the  ribs  is  accompanied  by  a  slight  opening 
out  of  the  angle  which  the   bony  part  forms   with   its   cartilage 


Fig.  156. — Diagram  of  movement  of  a  rib  in  inspiration. 


(fig.    156,  A);   and    thus    an    additional    means    is    provided  for 
increasing  the  antero-posterior  diameter  of  the  chest. 

The  muscles  by  which  the  ribs  arc  raised,  in  ordinary  quiet 
inspiration,  are  the  external  intercostals,  and  that  portion  of  the 
internal  intercostals  which  is  situate  between  the  costal  cartilages ; 
and  these  are  assisted  by  the  levatores  costarum,  and  the  serratus 
posticus  superior.  The  action  of  the  levatores  and  the  serratus 
is  very  simple.  Their  fibres,  arising  from  the  spine  as  a  fixed 
point,  pass  obliquely  downwards  and  forwards  to  the  ribs,  and 
necessarily  raise  the  latter  when  they  contract.  The  action  of 
the  intercostal  muscles  is  not  quite  so  simple,  inasmuch  as, 
passing  merely  from  rib  to  rib,  they  seem  at  first  sight  to  have 


230 


RESPIRATION. 


[chap.  VI. 


C'/, 


n' 


t^t 


%J 


D 


no  fixed  point  towards  which  they  can  pull  the  bones  to  which 
they  are  attached. 

A  very  simple  apparatus  will  explain  this  apparent  anomaly  and  make 
their  action  plain.     Such  an  apparatus  is  shown  in  rig.  157.     A  B  is  an 

upright  bar.  representing   the  spine, 
,5  with   which  are  jointed  two  parallel 

,;>;'[  bars,  C  and  D,  which  represent   two 

s's'    ij  of    the    ribs,   and    are    connected   in 

A  y?  front    by   moveable    joints    with   an- 

il- other  upright,  representing  the  ster- 

num. 

If  with  such  an  apparatus  elastic 
bands  be  connected  in  imitation  of 
the  intercostal  muscles,  it  will  be 
found  that  when  stretched  on  the  bars 
after  the  fashion  of  the  external  inter- 
costal fibres  (fig.  157,  C  D).  i.e  ,  passing 
downwards  and  forwards,  they  raise 
them  (fig.  157  C  D')  ;  while  on  the  other 
hand,  if  placed  in  imitation  of  the 
position  of  the  internal  intercostals- 
(tig.158 ,  E  F),  -i.e.,  passing  downwards 
and  backwards,  they  depress  them 
(fig.  158,  E'  F'). 

The  explanation  of   the    foregoing 
facts  is  very  simple.     The  intercostal 
muscles,    in    contracting,   merely    do- 
that  which  all  other  contracting  fibres  do,  viz.,  bring  nearer  together  the 
points  to  which  they  are  attached ;  and  in  order  to  do  this,  the  external 

intercostals  must  raise  the  ribs,  the 
points  C  and  D  (fig.  157)  being  nearer 
to  each  other  when  the  parallel  bars- 
are  in  the  position  of  the  dotted  lines. 
The  limit  of  the  movement  in  the 
apparatus  is  reached  when  the  elastic 
band  extends  at  right  angles  to  the 
two  bars  which  it  connects — the  points- 
of  attachment  C  and  D'  being  then  at 
the  smallest  possible  distance  one 
from  the  other. 

The  internal  intercostals  (excepting 
those  fibres  which  are  attached  to  the 
cartilages  of  the  ribs),  have  an  oppo- 
site action  to  that  of  the  external.  In 
contracting  they  must  pull  down  the 
ribs,  because  the  points  E  and  F  (fig. 
158)  can  only  be  brought  nearer  one 
to  another  (fig.  158,  E'EF')  by  such  an 
alteration  in  their  position. 
On  account  of  the  oblique  position  of  the  cartilages  of  the  ribs  with  refer- 
ence to  the  sternum,  the  action  of  the  inter-cartilaginous  fibres  of  the  internal 


U 

J5 


Fig.  157. — Diagram  of  apparatus  showing 
the  action  of  the  external  intercostal  muscles. 


Fig.  158. — Diagram  of  apparatus  showing 
the  action  of  the  internal  intercostal  muscles. 


chap,  vi.]  EXPIRATION.  231 

intercostala  must,  of  course,  on  tlic  foregoing  principles,  resemble  that  of  the 
external  intercostala. 


In  tranquil  breathing,  the  expansive  movements  of  the  lower 
part  of  fche  chest  are  greater  than  those  of  the  upper.  In  forced 
inspiration,  on  the  other  hand,  the  greatest  extent  of  movement 
appears  to  be  in  the  upper  antero-posterior  diameter. 

Muscles  of  Extraordinary  Inspiration. — In  extraordinary 
or  forced  inspiration,  as  in  violent  exercise,  or  in  cases  in  which 
there  is  some  interference  with  the  due  entrance  of  air  into  the 
chest,  and  in  which,  therefore,  strong  efforts  are  necessary,  other 
muscles  than  those  just  enumerated,  are  pressed  into  the  service. 
It  is  very  difficult  or  impossible  to  separate  by  a  hard  and  fast 
line,  the  so-called  muscles  of  ordinary  from  those  of  extraordinary 
Inspiration  ;  but  there  is  no  doubt  that  the  following  are  but  little 
used  as  respiratory  agents,  except  in  cases  in  which  unusual  efforts 
are  required — the  scaleni  muscles,  the  sternomastoid,  the  serratus 
magnus,  the  pectorales,  and  the  trapezius. 

Types  of  Respiration. — The  expansion  of  the  chest  in  inspi- 
tation  presents  some  peculiarities  in  different  persons.  In  young 
children,  it  is  effected  chiefly  by  the  diaphragm,  which  being 
highly  arched  in  expiration,  becomes  flatter  as  it  contracts,  and, 
descending,  presses  on  the  abdominal  viscera,  and  pushes  forward 
the  front  walls  of  the  abdomen.  The  movement  of  the  abdominal 
walls  being  here  more  manifest  than  that  of  any  other  part,  it  is 
usual  to  call  this  the  abdominal  type  of  respiration.  In  men, 
together  with  the  descent  of  the  diaphragm,  and  the  pushing 
forward  of  the  front  wall  of  the  abdomen,  the  chest  and  the 
sternum  are  subject  to  a  wide  movement  in  inspiration  {inferior 
costal  type).  In  women,  the  movement  appears  less  extensive  in 
the  lower,  and  more  so  in  the  upper,  part  of  the  chest  (superior 
costal  type).     (See  figs.  159,  160.) 

B.  Expiration. — From  the  enlargement  produced  in  inspira- 
tion, the  chest  and  lungs  return  in  ordinary  tranquil  expiration,  by 
their  elasticity  ;  the  force  employed  by  the  inspiratory  muscles  in 
distending  the  chest  and  overcoming  the  elastic  resistance  of  the 
lungs  and  chest-walls,  being  returned  as  an  expiratory  effort  when 
the  muscles  are  relaxed.  This  elastic  recoil  of  the  lungs  is  suffi- 
cient, in  ordinary  quiet  breathing,  to  expel  air  from  the  chest  in 


232 


JRESPIRATIOX. 


[CHAP.  VI. 


the  intervals  of  inspiration,  and  no  muscular  power  is  required. 
In  all  voluntary  expiratory  efforts,  however,  as  in  speaking,  sing- 
ing, blowing,  and  the  like,  and  in  many  involuntary  actions 
also,  as  sneezing,  coughing,  etc.,  something  more  than  merely 
passive  elastic  power  is  necessary,  and  the  proper  expiratory 
muscles  are  brought  into  action.     By  far  the  chief  of  these  are 


Fig.  159. — The  changes  of  the  thoracic  and 
abdominal  walls  of  the  mule  during  respv- 
ration.  The  back  is  supposed  to  be  fixed, 
in  order  to  throw  forward  the  respira- 
tory movement  as  much  as  possible. 
The  outer  black  continuous  line  in  front 
represents  the  ordinary  breathing  move- 
ment :  the  anterior  margin  of  it  being 
the  boundary  of  inspiration,  the  poste- 
rior margin  the  limit  of  expiration. 
The  line  is  thicker  over  the  abdomen, 
since  the  ordinary  respiratory  move- 
ment is  chiefly  abdominal :  thin  over 
the  chest,  for  there  is  less  movement 
over  that  region.  The  dotted  line  indi- 
cates the  movement  on  deep  inspiration, 
during  which  the  sternum  advances 
while  the  abdomen  recedes. 


Fig.  160. — The  respiratory  movement  in  the 

female.  The  lines  indicate  the  same 
changes  as  in  the  last  figure.  The 
thickness  of  the  continuous  line  over 
the  sternum  shows  the  larger  extent 
of  the  ordinary  breathing  movement 
over  that  region  in  the  female  than  in 
the  male.     (John  Hutchinson.) 


The  posterior  continuous  line  represents 
in  both  figures  the  limit  of  forced  expi- 
ration. 


the  abdominal  muscles,  which,  by  pressing  on  the  viscera  of  the 
abdomen,  push  up  the  floor  of  the  chest  formed  by  the  diaphragm, 
and  by  thus  making  pressure  on  the  lungs,  expel  air  from  them 
through  the  trachea  and  larynx.  All  muscles,  however,  which 
depress  the  ribs,  must  act  also  as  muscles  of  expiration,  and  there- 
fore we  must  conclude  that  the  abdominal  muscles  are  assisted  in 


.:•.  vi.]  SPIRATO]  S     90TJX]  233 

their  action  bj  I       g      ter  part  of  the  the 

triangularit   -'       .   the  a  itai 

lumborum.     When   by  thi  3,  the 

chest       a    eon  squ<  to  _  ter,  it  ag  tin, 

relaxation  of  the  muscles,  returns  t< »  the  normal  din. 
vinue  of  its  elasticity.     The  construction  of  the        --     tils,  tin 
fore,  admirably  adapts  them  :  ling     gainst  an 

well  undue  contraction  as  undue  dilatation. 

In  the  natural  condition  of  the  ]      ts,  1  _-  never  con- 

tract to  the  utmost,  but  are  always  more     'less  u    a  th<    stretch," 

og  kept  closely  in  contact  with  the  inner  surface  of  the  walls 
the  chest  by  atmospheric  press  .  aid  can  contract  away  from 
these  only  when,  by  some  means  or  other,  -  making  an  open- 
ing into  the  pleural  cavi:  y  the  eftusion  of  fluid  there,  the 
pre—  d  the  exterior  and  interior  of  the  lungs  becomes  equal. 
Thus,  under  ordinary  circumstances,  the 
dilatation  of  the  lungs    -  dependent  on  that  of  the  boundary  walls 

the  chest,  th        iter  surfat     of  the  one  being  inclose  contact 
with  the  inner  -  of  the  other,  and  obliged  to  follow  it  in  all 

lovements. 

Respiratory  Rhythm. — The     its    :  .-ion  and  contraction 

of  the  ch  st>  i  .  under  ordinary  circumstances,  a  nearly  equal 

time.  The  act  of  inspiring  air,  however.,  -  illy  in  women  and 
children,  is  a  little  shorter  than  that  of  expelling  it,  and  there  is 
commonly  a  very  slight  pause  between  the  end  of  expiration  and 
the  beginning  i  t  the  next  inspiration.  The  respiratory  rhythm 
may  be  thus  expressed  : — 

Inspiration         ......  6 

Expiration    .         .         .         .         .         .     .  7  or  S 

A  very  sligli:  pause. 

Respiratory  Sounds. — If  the  ear  be  placed  in  c  ^  itli 

the  wall  of  the  chest,  or  be  separated  from  it  only  by  a  good 
conductor  of  sound,  a  faint  torv  murmur  is  heard  during 

inspiration.     This  sound  a    somewhat   in   different    parts — 

being  loudest  or  o    tsesf  in  the  neighbourhood  i  and 

large  bronchi  (tracheal  and  bronchial  breathing;,  and  fading  off 

into  a  faint  -  og  as  the  ear  is  pi  from  tL 

(vesicular  breathing).     It  is  best  in  children,  and  in  them 


234  INSPIRATION.  [chap.  vt. 

a  faint  murmur  is  heard  in  expiration  also.  The  cause  of  the 
vesicular  murmur  has  received  various  explanations.  Most 
observers  hold  that  the  sound  is  produced  by  the  friction  of  the 
air  against  the  walls  of  the  alveoli  of  the  lungs  when  they  are 
undergoing  distension  (Laennec,  Skoda),  others  that  it  is  due  to 
an  oscillation  of  the  current  of  air  as  it  enters  the  alveoli 
(Chauveau),  whilst  others  believe  that  the  sound  is  produced  in 
the  glottis,  but  that  it  is  modified  in  its  passage  to  the  pulmonary 
alveoli  (Beau,  Gee). 

Respiratory  Movements  of  the  Nostrils  and  of  the 
Glottis. — During  the  action  of  the  muscles  which  directly  draw 
air  into  the  chest,  those  which  guard  the  opening  through  which 
it  enters  are  not  passive.  In  hurried  breathing  the  instinctive 
dilatation  of  the  nostrils  is  well  seen,  although  under  ordinary 
conditions  it  may  not  be  noticeable.  The  opening  at  the  upper 
part  of  the  larynx,  however,  or  rima  glottidis  (fig.  297),  is  dilated 
at  each  inspiration,  for  the  more  ready  passage  of  air,  and  becomes 
smaller  at  each  expiration  ;  its  condition,  therefore,  corresponding 
during  respiration  with  that  of  the  walls  of  the  chest.  There  is  a 
further  likeness  between  the  two  acts  in  that,  under  ordinary 
circumstances,  the  dilatation  of  the  rima  glottidis  is  a  muscular 
act,  and  its  contraction  chiefly  an  elastic  recoil ;  although,  under 
various  conditions,  to  be  hereafter  mentioned,  there  may  be,  in  the 
contraction  of  the  glottis,  considerable  muscular  power  exercised. 

Terms  used  to  express  Quantity  of  Air  breathed.— 
Breathing  or  tidal  air,  is  the  quantity  of  air  which  is  habitually 
and  almost  uniformly  changed  in  each  act  of  breathing.  In  a 
healthy  adult  man  it  is  about  30  cubic  inches. 

Complemental  air,  is  the  quantity  over  and  above  this  which  can 
be  drawn  into  the  lungs  in  the  deepest  inspiration ;  its  amount  is 
various,  as  will  be  presently  shown. 

Reserve  air.  After  ordinary  expiration,  such  as  that  which 
expels  the  breathing  or  tidal  air,  a  certain  quantity  of  air  remains 
in  the  lungs,  which  may  be  expelled  by  a  forcible  and  deeper 
expiration.     This  is  termed  reserve  air. 

Residual  air  is  the  quantity  which  still  remains  in  the  lungs 
after  the  most  violent  expiratory  effort.  Its  amount  depends  in 
great  measure  on  the  absolute  size  of  the  chest,  but  may  be  esti- 
mated at  about  100  cubic  inches. 


obat,  vi.]  RESPIRATORY.    CAPACITY.  235 

The  total  quantity  of  air  which  passes  into  and  oul  of  the  Lungs 
of  an  adult,  at  rest,  in  24  hours,  is  about  686,000  cubic  inch) 
'This   quantity,   however,  is   largely    increased    by   ei  srtion  ;   tin- 
average  amount  tV>r  a  hard-working  labourer  in  the  same  tin 
being  1,568,390  cubic  inches. 

Respiratory  <'<ii»iritij. — The  greatest  respiratory  capacity  of  the 
chest  is  indicated  by  the  quantity  of  air  which  a  person  can  expel 
from  his  lungs  by  a  forcible  expiration  after  the  deepest  inspiration 
that  he  ean  make;  it  expresses  the  power  which  a  person  has  of 
breathing  in  the  emergencies  of  active  exercise,  violence,  ami 
disease.  The  average  capacity  of  an  adult  (at  6o°F.  or  15*4°  ('.) 
is  about  225  cubic  inches. 

The  respiratory  capacity,  or  as  Hutchinson  called  it.  vital  capacityr 
is  usually  measured  by  a  modified  gasometer  (spirometer  of  Hutchinson), 
into  which  the  experimenter  breathes, — making  the  most  prolonged  expira- 
tion possible  after  the  deepest  possible  inspiration.  The  quantity  of  air 
which  is  thus  expelled  from  the  lungs  is  indicated  by  the  height  to  which 
the  air  chamber  of  the  spirometer  rises  ;  and  by  means  of  a  scale  placed  in 
connection  with  this,  the  number  of  cubic  inches  is  read  off. 

Ill  healthy  men,  the  respiratory  capacity  varies  chiefly  with  the 
stature,  weight,  and  age. 

It  was  found  by  Hutchinson,  from  whom  most  of  our  infor- 
mation on  this  subject  is  derived,  that  at  a  temperature  of  6o°  I'., 
225  cubic  inches  is  the  average  vital  or  respiratory  capacity  of  a 
healthy  person,  five  feet  seven  inches  in  height. 

Circumstance*  affecting  the  amount  of  respiratory  capacity. — For  every 
inch  of  height  above  this  standard  the  capacity  is  increased,  on  an  average, 
by  eight  cubic  inches;  and  for  every  inch  below,  it  is  diminished  by  the 
same  amount. 

The  influence  of  weight  on  the  capacity  of  respiration  is  less  manifest  and 
considerable  than  that  of  height  :  and  it  is  difficult  to  arrive  at  any  definite 
conclusions  on  this  point,  because  the  natural  average  weight  of  a  healthy 
man  in  relation  to  stature  has  not  yet  been  determined.  As  a  general  state- 
ment, however,  it  may  he  said  that  the  capacity  of  respiration  is  not  affected 
by  weights  under  161  pounds,  or  wh  stones  ;  but  that,  above  this  point,  it  is 
diminished  at  the  rate  of  one  cubic  inch  for  every  additional  pound  up  to 
196  pounds,  or  14  stones. 

By  age,  the  capacity  appears  to  be  increased  from  about  the  fifteenth  to 
the  thirty-fifth  year,  at  the  rate  of  five  cubic  inches  per  year  :  from  thirty- 
five  to  sixty-five  it  diminishes  at  the  rate  of  about  one  and  a  half  cubic  inch 
per  year  ;  so  that  the  capacity  of  respiration  of  a  man  of  sixty  years  old 
would  be  about  30  cubic  inches  less  than  that  of  a  man  forty  years  old, 
of  the  same  height  and  weight.     (John  Hutchinson.) 


2 $6  RESPIRATION.  [chap.  vi. 

Number  of  Respirations,  and  Relation  to  the  Pulse.— 
The  number  of  respirations  in  a  healthy  adult  person  usually 
ranges  from  fourteen  to  eighteen  per  minute.  It  is  greater  in 
infancy  and  childhood.  It  varies  also  much  according  to  different 
circumstances,  such  as  exercise  or  rest,  health,  or  disease,  etc. 
Variations  in  the  number  of  respirations  correspond  ordinarily  with 
similar  variations  in  the  pulsations  of  the  heart.  In  health  the 
proportion  is  about  i  to  4,  or  1  to  5,  and  when  the  rapidity  of  the 
heart's  action  is  increased,  that  of  the  chest  movement  is  commonly 
increased  also  ;  but  not  in  every  case  in  equal  proportion.  It 
happens  occasionally  in  disease,  especially  of  the  lungs  or  air- 
passages,  that  the  number  of  respiratory  acts  increases  in  quicker 
proportion  than  the  beats  of  the  pulse;  and,  in  other  affections, 
much  more  commonly,  that  the  number  of  the  pulses  is  greater  in 
proportion  than  that  of  the  respirations. 

There  can  be  no  doubt  that  the  number  of  respirations  of  any  given  animal 
is  largely  affected  by  its  size.  Thus,  comparing  animals  of  the  same  kind,  in 
3l  tiger  (lying  quietly)  the  number  of  respirations  was  20  per  minute,  while 
in  a  small  leopard  (lying  quietly)  the  number  was  30.  In  a  small  monkey 
40  per  minute  ;  in  a  large  baboon,  20. 

The  rapid,  panting  respiration  of  mice,  even  when  quite  still,  is  familiar, 
and  contrasts  strongly  with  the  slow  breathing  of  a  large  animal  such  as  the 
elephant  (eight  or  nine  times  per  minute).  These  facts  maybe  explained  as 
follows  : — The  heat-producing  power  of  any  given  animal  depends  largely 
on  its  bulk,  while  its  loss  of  heat  depends  to  a  great  extent  upon  the  surface 
area  of  its  body.  If  of  two  animals  of  similar  shape,  one  be  teii  times  as 
long  as  the  other,  the  area  of  the  large  animal  (representing  its  loss  of  heat) 
is  100  times  that  of  the  small  one,  while  its  bulk  (representing  production 
-of  heat)  is  about  1000  times  as  great.  Thus  in  order  to  balance  its  much 
greater  relative  loss  of  heat,  the  smaller  animal  must  have  all  its  vital 
functions,  circulation,  respiration,  &c.,  carried  on  much  more  rapidly. 

Force  of  Inspiratory  and  Expiratory  Muscles.— The  force 
with  which  the  inspiratory  muscles  are  capable  of  acting  is 
greatest  in  individuals  of  the  height  of  from  five  feet  seven  inches 
to  five  feet  eight  inches,  and  will  elevate  a  column  of  three  inches 
of  mercury.  Above  this  height,  the  fore  decreases  as  the  stature 
increases  ;  so  that  the  average  of  men  of  six  feet  can  elevate  only 
about  two  and  a  half  inches  of  mercury.  The  force  manifested  in 
the  strongest  expiratory  acts  is,  on  the  average,  one-third  greater 
than  that  exercised  in  inspiration.  But  this  difference  is  in  great 
measure  due  to  the  power  exerted  by  the  elastic  reaction  of  the 
walls  of  the  chest  ;  and  it  is  also  much  influenced  by  the  dkpro- 


chap,  vl]    force  op   inspiration  and   EXPIRATION.     237 

portionate   strength  which    tin-   expiratorj   muscl  in,   from 

their  being  called  into  use  for  other  purposes  tliiin  that  of  simple 
expiration.     The  force  of  the  inspiratory 

adapted   than   that  of  the  expiratory  for   testing  the  muscular 
strength  of  the  body.     (John  Butchinsou.) 

instmmi         -    I  by  Hutchinson  I  the  inspiratory  and  expira- 

tory power  was  a  mercurial  manometer, to  which  was  attached  a  tube  fitting 
the  iio.<t ril<.  and  through  which  the  inspiratory  <-r  expiratory  effort  was 
table  repi  3  of  numerous  experimi 


r  of 

irator; 

15  in.      . 

.     Weak      . 

Pov. 
Expiratory  Muscles. 
.     20  in. 

20  .. 

Ordinary     . 

2-5  .. 

-■5    ••        • 
3'5  •• 
45  ••       • 

Strong 
Very 

Remarka'; 

•  35  •• 

•  5 

5"5  •• 

Very  remark 

70  .. 

60  ..      . 

Extraordinary 

.    S-5  .. 

7-0  .. 

Very  extraordinary 

100  ., 

The  greater  part  of  the  force  exerted  in  deep  inspiration  is 
employed  in  overcoming  the  resistance  offered  by  the  elasticity  of 
the  walls  of  the  chest  and  of  the  lungs. 


*- 


The  amount  of  this  elastic  resistance  was  estimated  by  observing  the 
elevation  of  a  column  of  mercury  raised  by  the  return  of  air  forced,  after 
death,  into  the  lungs,  in  quantity  equal  to  the  known  capacity  of  respiration 
during  life  ;  and  Hutchin-on  calculated,  according  to  the  well-known  hydro- 
static law  of  equality  of  prese  -  as  >hown  in  the  Bramah  press),  that  the 
total  force  to  be  overcome  by  the  muscles  in  the  act  of  inspiring  200  cubic 
inches  of  air  is  more  than  450  lbs. 

The  elastic  force  overcome  in  ordinary  inspiration  i-.  according  to  the 
same  authority,  equal  to  about  170  lbs. 

Douglas  Powell  has  shown  that  within  the  limits  of  ordinary 
tranquil  respiration^  the  elastic  resilience  of  the  walls  of  the 
favours  inspiration  ;  and  that  it  is  only  in  deep  inspiration  that 
the  ribs  and  rib-cartilages  offer  an  opposing  force  t<>  their  dilata- 
tion. In  other  words,  the  elastic  resilience  of  the  lungs,  at  the 
end  of  an  act  of  ordinary  breathing,  has  drawn  the  chest-walls 
within  the  limits  of  their  normal  degree  of  expansion.  Under  all 
circumstances,  of  course,  the  elastic  tissue  of  the  lungs  opposes 
inspiration,  and  favours  expiration. 

Functions  of  Muscular  Tissue  of  Lungs. — It  is  possible 
that  the  contractile  power  which  the  bronchial  tubes  and  air-vesicles 


238  RESPIRATION.  [chap.  vi. 

possess,  by  means  of  their  muscular  fibres  may  (1)  assist  in  expira- 
tion ;  bnt  it  is  more  likely  that  its  chief  purpose  is  (2)  to  regulate 
.and  adapt,  in  some  measure,  the  quantity  of  air  admitted  to  the 
lungs,  and  to  each  part  of  them,  according  to  the  supply  of  blood ; 
(3)  the  muscular  tissue  contracts  upon  and  gradually  expels  collec- 
tions of  mucus,  which  may  have  accumulated  within  the  tubes, 
and  cannot  be  ejected  by  forced  expiratory  efforts,  owing  to  collapse 
or  other  morbid  conditions  of  the  portion  of  lung  connected  with 
the  obstructed  tubes  (Gairdner).  (4)  Apart  from  any  of  the  before- 
mentioned  functions,  the  presence  of  muscular  fibre  in  the  walls 
of  a  hollow  viscus,  such  as  a  lung,  is  only  what  might  be  expected 
from  analogy  with  other  organs.  Subject  as  the  lungs  are  to 
such  great  variation  in  size  it  might  be'  anticipated  that  the 
clastic  tissue,  which  enters  so  largely  into  their  composition, 
would  be  supplemented  by  the  presence  of  much  muscular  fibre 
also. 

Respiratory  Changes  in  the  Air  and  in  the  Blood. 

A.  In  the  Air. 

Composition  of  the  Atmospliere. — The  atmosphere  we  breathe  has, 
in  every  situation  in  which  it  has  been  examined  in  its  natural 
state,  a  nearly  uniform  composition.  It  is  a  mixture  of  oxygen, 
nitrogen,  carbonic  acid,  and  watery  vapour,  with,  commonly,  traces 
of  other  gases,  as  ammonia,  sulphuretted  hydrogen,  &c.  Of  every 
100  volumes  of  pure  atmospheric  air,  79  volumes  (on  an  average) 
consist  of  nitrogen,  the  remaining  21  of  oxygen.  By  weight 
the  proportion  is  N.  75,  0.  25.  The  proportion  of  carbonic  acid  is 
extremely  small;  10,000  volumes  of  atmospheric  air  contain  only 
about  4  or  5  of  carbonic  acid. 

The  quantity  of  watery  vapour  varies  greatly  according  to 
the  temperature  and  other  circumstances,  but  the  atmosphere  is 
never  without  some.  In  this  country,  the  average  quantity  of 
watery  vapour  in  the  atmosphere  is  1*40  per  cent. 

Composition  of  Air  which  has  been  breathed.  —  The  changes 
effected  by  respiration  in  the  atmospheric  air  are  :  1,  an  increase 
of  temperature  ;  2,  an  increase  in  the  quantity  of  carbonic  acid ; 
3,  a  diminution  in  the  quantity  of  oxygen ;  4,  a  diminution  of 
volume ;  5,  an  increase  in  the  amount  of  watery  vapour ;  6,  the 
addition  of  a  minute  amount  of  organic  matter  and  of  free  ammonia. 


chap,  yi.]  RESPIRATORY    CHANGES    OF    AIE.  239 

1.  The  expired  air,  heated  by  its  contact  with  tin:  interior  of 
the  lungs,  is  (at  least  in  most  climates)  hotter  thai]  the 
inspired  air.  It>.  temperature  varies  between  97'  and  99. 50  F. 
(36° —  37*5°  C),  the  lower  temperature  being  observed  when  the  air 

has  remained  but  a  short  time  in  the  lungs.  Whatever  may  be 
the  temperature  of  the  air  when  inhaled,  it  nearly  acquires  that  of 
the  blood  before  it  i>  expelled  from  the  chest. 

2.  The  Carbonic  Acid  in  respired  air  is  always  increased; 
but  the  quantity  exhaled  in  agiveo  time  is  subject  to  change  from 
various  circumstances.  From  every  volume  of  air  inspired,  about 
4*8  per  cent,  of  oxygeo  is  abstracted;  while  a  rather  smaller 
quantity,  4*3,  of  carbonic  acid  is  added  in  its  place  :  the  air  will 
contain,  therefore,  434  vols,  of  carbonic  acid  in  10,000.  Under 
ordinary  circumstances,  the  quantity  of  carbonic  acid  exhaled  into* 
the  air  breathed  by  a  healthy  adult  man  amounts  to  1346  cubic 
inches,  or  about  636  grains  per  hour.  According  to  this  estimate, 
the  weight  of  carl  ion  excreted  from  the  lungs  is  about  173  grains 
per  hour,  or  rather  more  than  8  ounces  in  twenty-four  hours. 
These  quantities  must  be  considered  approximate  only,  inasmuch 
as  various  circumstances,  even  in  health,  influence  the  amount  of 
carbonic  acid  excreted,  and,  correlatively,  the  amount  of  oxygen 
absorbed. 


Circumstances  influencing  the  amount  of  carbonic  acid  excreted. — The 
following  are  the  chief : — Age  and  sex.  Respiratory: movements.  External 
temperature.  Season  of  year.  Condition  of  respired  air.  Atmospheric 
conditions.     Period  of  the  day.     Food  and  drink.     Exercise  and  sleep. 

a.  Ar/e  and  Sex. — The  quantity  of  carbonic  acid  exhaled  into  the  air 
breathed  by  males,  regularly  increases  from  eight  to  thirty  years  of  age  ; 
from  thirty  to  fifty  the  quantity,  after  remaining  stationary  for  awhile, 
gradually  diminishes,  and  from  fifty  to  extreme  age  it  goes  on  diminishing, 
till  it  scarcely  exceeds  the  quantity  exhaled  at  ten  years  old.  In  females 
(in  whom  the  quantity  exhaled  is  always  less  than  in  males  of  the  same 
age)  the  same  regular  increase  in  quantity  goes  on  from  the  eighth  year  to 
the  age  of  puberty,  when  the  quantity  abruptly  ceases  to  increase,  and 
remains  stationary  so  long  as  they  continue  to  menstruate.  \\  hen 
menstruation  has  ceased,  it  soon  decreases  at  the  same  rate  as  it  does  in 
old  men. 

b.  Respiratory  Movements.— The  more  quickly  the  movements  of  respira- 
tion are  perf ormed,  the  smaller  is  the  proportionate  quantity  of  carbonic  acid 
contained  in  each  volume  of  the  expired  air.  Although,  however,  the  pro- 
portionate quantity  of  carbonic  acid  is  thus  diminished  during  frequent 
respiration,  yet  the  absolute  amount  exhaled  into  the  air  within  a  given 


240  RESPIRATION.  [uHAje.  vi. 

time  is  increased  thereby,  owing  to  the  larger  quantity  of  air  which  is 
breathed  in  the  time.  The  last  half  of  a  volume  of  expired  air  contains- 
more  carbonic  acid  than  the  half  first  expired ;  a  circumstance  which  is. 
explained  by  the  one  portion  of  air  coming  from  the  remote  part  of  the 
lungs,  where  it  has  been  in  more  immediate  and  prolonged  contact  with 
the  blood  than  the  other  has,  which  comes  chiefly  from  the  larger  bronchial 
tubes. 

c.  External  temperature. — The  observation  made  by  Vierordt  at  various 
temperatures  between  38°  F.  and  750  F.  (3-4°— 23-8°  C.)  show,  for  warm- 
blooded animals,  that  within  this  range,  every  rise  equal  to  io°  F.  causes  a 
diminution  of  about  two  cubic  inches  in  the  quantity  of  carbonic  acid 
exhaled  per  minitte. 

d.  Season  of  tJie  Year. — The  season  of  the  year,  independently  of  tempe- 
rature, materially  influences  the  respiratory  phenomena  ;  spring  being  the 
season  of  the  greatest,  and  autumn  of  the  least  activity  of  the  respiratory 
and  other  functions.     (Edward  Smith.) 

e.  Purity  of  tlie  Respired  Air. — The  average  quantity  of  carbonic  acid 
given  out  by  the  lungs  constitutes  about  4-3  per  cent,  of  the  expired  air  ; 
but  if  the  air  which  is  breathed  be  previously  impregnated  with  carbonic 
acid  (as  is  the  case  when  the  same  air  is  frequently  respired),  then  the 
quantity  of  carbonic  acid  exhaled  becomes  much  less. 

/.  Ilyyrometrie  State  of  Atmosphere.-— The  amount  of  carbonic  acid 
exhaled  is  considerably  influenced  by  the  degree  of  moisture  of  the  atmo- 
sphere, much  more  being  given  off  when  the  air  is  moist  than  when  it  is  dry. 
(Lehmann.) 

g.  Period  of  the  Day. — During  the  day-time  more  carbonic  acid  is  exhaled 
than  corresponds  to  the  oxygen  absorbed  :  while,  on  the  other  hand,  at  night 
very  much  more  oxygen  is  absorbed  than  is  exhaled  in  carbonic  acid. 
There  is.  thus,  a  reserve  fund  of  oxygen  absorded  by  night  to  meet  the 
requirements  of  the  day.  If  the  total  quantity  of  carbonic  acid  exhaled 
in  24  hours  be  represented  by  100,  52  parts  are  exhaled  during  the 
day,  and  48  at  night.  While,  similarly,  33  parts  of  the  oxygen  are 
absorbed  during  the  day,  and  the  remaining  67  by  night.  (Pettenkofer 
and  Voit.) 

h.  Food  and  Brink. — By  the  use  of  food  the  quantity  is  increased.  Avhilst 
by  fasting  it  is  diminished  ;  it  is  greater  when  animals  are  fed  on  farinaceous 
food  than  when  fed  on  meat.  The  effects  produced  by  spirituous  drinks 
depend  much  on  the  kind  of  drink  taken.  Pure  alcohol  tends  rather  to 
increase  than  to  lessen  respiratory  changes,  and  the  amount  therefore  of 
carbonic  acid  expired  ;  ram,  ale,  and  porter,  also  sherry,  have  very  similar 
effects.  On  the  other  hand,  brandy,  whisky,  and  gin,  particularly  the  latter, 
almost  always  lessened  the  respiratory  changes,  and  consequently  the 
amount  of  carbonic  acid  exhaled.     (Edward  Smith.) 

i.  Exercise. — Bodily  exercise,  in  moderation,  increases  the  quantity  to 
about  one-third  more  than  it  is  during  rest :  and  for  about  an  hour  after 
exercise  the  volume  of  the  air  expired  in  the  minute  is  increased  about  118 
cubic  inches  :  and  the  quantity  of  carbonic  acid  about  7-8  cubic  inches  per 
minute.  Violent  exercise,  such  as  full  labour  on  the  treadwheel,  still  further 
increases  the  amount  of  the  acid  exhaled.     (Edward  Smith.) 

A  larger  quantity  is  exhaled  when  the  barometer  is  low  than  when  it  is 
high. 


chap.yl]  CHANGES    OF   THE   AIR. 


241 


3.  The  oxygen  is  diminished,  and  its  diminution  is  generally 
proportionate  to  the  increase  of  the  carbonic  acid. 

For  every  volume  of  carbonic  acid  exhaled  into  the  air,  1-17421 
volumes  of  oxygen  arc  absorbed  from  it,  and  1346  cubic  inches,  or 
636  grains  being  exhaled  in  the  hour  the  quantity  of  oxygen 
absorbed  in  the  same  time  is  1584  cubic  inches,  or  542  grains. 
According  to  this  estimate,  there  is  more  oxygen  absorbed  than 
is  exhaled  with  carbon  to  form  carbonic  acid. 

4.  The  volume  of  air  expired  in  a  given  time  is  less  than  that 
of  the  air  inspired  (allowance  being  made  for  the  expansion  in 
being  heated),  and  that  the  loss  is  due  to  a  portion  of  oxygen 
absorbed  and  not  returned  in  the  exhaled  carbonic  acid,  all 
observers  agree,  though  as  to  the  actual  quantity  of  oxygen  so 
absorbed,  they  differ  even  widely.  The  amount  of  oxygen 
absorbed  is  on  an  average  4*8  per  cent,  so  that  the  expired  air 
contains  16*2  volumes  per  cent,  of  that  gas. 

The  quantity  of  oxygen  that  does  not  combine  with  the  carbon  given  off 
in  carbonic  acid  from  the  lungs  is  probably  disposed  of  in  forming  some  of 
the  carbonic  acid  and  water  given  off  from  the  skin,  and  in  combining  with 
sulphur  and  phosphorus  to  form  part  of  the  acids  of  the  sulphates  and 
phosphates  excreted  in  the  urine,  and  probably  also,  with  the  nitrogen  of 
the  decomposing  nitrogenous  tissues.     (Bence  Jones.) 

The  quantity  of  oxygen  in  the  atmosphere  surrounding  animals, 
appears  to  have  very  little   influence  on  the  amount  of  this   gas 
absorbed  by  them,  for  the  quantity  consumed  is  not  greater  even 
though  an  excess  of  oxygen  be  added  to  the   atmosphere  experi 
mented  with. 

It  has  often  been  discussed  whether  Nitrogen  is  absorbed  by  or 
exhaled  from  the  lungs  during  respiration.  At  present,  all  that 
can  be  said  on  the  subject  is  that,  under  most  circumstances, 
animals  appear  to  expire  a  very  small  quantity  above  that  which 
exists  in  the  inspired  air.  During  prolonged  fasting,  on  the  con- 
trary, a  small  quantity  appears  to  be  absorbed. 

5.  The  watery  vapour  is  increased.  The  quantity  emitted  is, 
as  a  general  rule,  sufficient  to  saturate  the  expired  air,  or  very 
nearly  so.  Its  absolute  amount  is,  therefore,  influenced  by  the 
following  circumstances,  (1),  by  the  quantity  of  air  respired  ;  for 
the  greater  this  is,  the  greater  also  will  be  the  quantity  of  moisture 

R 


242  RESPIRATION.  [chap.  vi. 

exhaled.  (2),  by  the  quantity  of  watery  vapour  contained  in  the 
air  previous  to  its  being  inspired ;  because  the  greater  this  is,  the 
less  will  be  the  amount  required  to  complete  the  saturation  of  the 
air ;  (3),  by  the  temperature  of  the  expired  air ;  for  the  higher 
this  is,  the  greater  will  be  the  quantity  of  watery  vapour  required 
to  saturate  the  air ;  (4),  by  the  length  of  time  which  each  volume 
of  inspired  air  is  allowed  to  remain  in  the  lungs ;  for  although, 
during  ordinary  respiration,  the  expired  air  is  always  saturated 
with  watery  vapour,  yet  when  respiration  is  performed  very 
rapidly  the  air  has  scarcely  time  to  be  raised  to  the  highest  tem- 
perature, or  be  fully  charged  with  moisture  ere  it  is  expelled. 

The  quantity  of  water  exhaled  from  the  lungs  in  twenty-four 
hours  ranges  (according  to  the  various  modifying  circumstances 
already  mentioned)  from  about  6  to  27  ounces,  the  ordinary 
quantity  being  about  9  or  10  ounces.  Some  of  this  is  probably 
formed  by  the  chemical  combination  of  oxygen  with  hydrogen  in 
the  system  ;  but  the  far  larger  proportion  of  it  is  water  which  has 
been  absorbed,  as  such,  into  the  blood  from  the  alimentary  canal, 
and  which  is  exhaled  from  the  surface  of  the  air-passages  and  cells, 
as  it  is  from  the  free  surfaces  of  all  moist  animal  membranes, 
particularly  at  the  high  temperature  of  warm-blooded  animals. 

6.  A  small  quantity  of  ammonia  is  added  to  the  ordinary 
constituents  of  expired  air.  It  seems  probable,  however,  both 
from  the  fact  that  this  substance  cannot  be  always  detected,  and 
from  its  minute  amount  when  present,  that  the  whole  of  it  may 
be  derived  from  decomposing  particles  of  food  left  in  the  mouth, 
or  from  carious  teeth  or  the  like  ;  and  that  it  is,  therefore,  only  an 
accidental  constituent  of  expired  air. 

7.  The  quantity  of  organic  matter  in  the  breath  is  about  3  grains 
in  twenty-four  hours.     (Ransome.) 

The  following  represents  the  kind  of  experiment  by  which  the  foregoing 
facts  regarding  the  excretion  of  carbonic  acid,  water,  and  organic  matter, 
have  been  established. 

A  bird  or  mouse  is  placed  in  a  large  bottle,  through  the  stopper  of  which 
two  tubes  pass,  one  to  supply  fresh  air,  and  the  other  to  carry  off  that  which 
has  been  expired.  Before  entering  the  bottle,  the  air  is  made  to  bubble 
through  a  strong  solution  of  caustic  potash,  which  absorbs  the  carbonic  acid, 
and  then  through  lime-water,  which  by  remaining  limpid,  proves  the  absence 
of  carbonic  acid.  The  air  which  has  been  breathed  by  the  animal  is  made 
to  bubble  through  lime  water,  which  at  once  becomes  turbid  and  soon  quite 
milky  from  the  precipitation  of  calcium  carbonate  ;  and  it  finally  passes 


CHAJ.YL]     METHOD    OF    THE    RESPIRATORY    CHANGE  243 

through  strong  sulphuric  acid,  which,  by  turning  brown,  indicates  the  pre- 
Bence  of  organic  matter,  The  watery  rapoui  in  the  expired  air  will  condense 
inside  the  bottle  if  the  surface  be  kept  cool. 

By  means  of  an  apparatus  sufficiently  large  and  well  constructed,  experi- 
ments of  the  kind  have  been  made  extensively  on  man. 


Methods  by  which  the  Respiratory   Changes  in  the  Air 

are   effected. 

The  method  by  which  fresh  air  is  inhaled  and  expelled  from 
the  lungs  has  been  considered.  It  remains  to  consider  how  it 
is  that  the  blood  absorbs  oxygen  from,  and  gives  up  carbonic  acid 
to,  the  air  of  the  alveoli.  In  the  first  place,  it  must  be  remem 
bered  that  the  tidal  air  only  amounts  to  about  25 — 30  cubic 
inches  at  each  inspiration,  and  that  this  is  of  course  insufficient  to 
fill  the  lungs,  but  it  mixes  with  the  stationary  air  by  diffusion, 
and  so  supplies  to  it  new  oxygen.  The  amount  of  oxygen  in  ex- 
pired air,  which  may  be  taken  as  the  average  composition  of  the 
mixed  air  in  the  lungs,  is  about  1 6  to  17  per  cent. ;  in  the  pulmo- 
nary alveoli  it  may  be  rather  less  than  this.  From  this  air  the 
venous  blood  has  to  take  up  oxygen  in  the  proportion  of  8  to  12 
vols,  in  every  hundred  volumes  of  blood,  as  the  difference  between 
the  amount  of  oxygen  in  arterial  and  venous  blood  is  no  less 
than  that.  It  seems  therefore  somewhat  difficult  to  understand 
how  this  can  be  accomplished  at  the  low  oxygen  tension  of  the 
pulmonary  air.  But  as  was  pointed  out  in  a  previous  Chapter 
(IV.),  the  oxygen  is  not  simply  dissolved  in  the  blood,  but  is  to  a 
great  extent  chemically  combined  with  the  haemoglobin  of  the  red 
corpuscles ;  and  when  a  fluid  contains  a  body  which  enters  into 
loose  chemical  combination  in  this  way  with  a  gas,  the  tension  of 
the  gas  in  the  fluid  is  not  directly  proportional  to  the  total  quan- 
tity of  the  gas  taken  up  by  the  fluid,  but  to  the  excess  above  the 
total  quantity  which  the  substance  dissolved  in  the  fluid  is  capable 
of  taking  up  (a  known  quantity  in  the  case  of  haemoglobin,  viz., 
1  "59  cm.  for  one  grm.  haemoglobin).  On  the  other  hand,  if  the 
substance  be  not  saturated,  i.e.,  if  it  be  not  combined  with  as 
much  of  the  gas  as  it  is  capable  of  taking  up,  further  combination 
leads  to  no  increase  of  its  tension.  However,  there  is  a  point  at 
which  the  haemoglobin  gives  up  its  oxygen  when  it  is  exposed  to 
a  low  partial  pressure  of  oxygen,  and  there  is  also  a  point  at  which 

r  2 


244  RESPIBATION.  [chap.  vi. 

it  neither  takes  up  nor  gives  out  oxygen ;  in  the  case  of  arterial 
blood  of  the  dog,  this  is  found  to  be  when  the  oxygen  tension  of 
the  atmosphere  is  equal  to  3-9  per  cent,  (or  29/6  mm.  of  mercury), 
which  is  equivalent  to  saying  that  the  oxygen  tension  of  arterial 
blood  is  3*9  per  cent.  ;  venous  blood,  in  a  similar  manner,  has 
been  found  to  have  an  oxygen  tension  of  2-8  per  cent.  At  a 
higher  temperature,  the  tension  is  raised,  as  there  is  a  greater 
tendency  at  a  high  temperature  for  the  chemical  compound  to 
undergo  dissociation.  It  is  therefore  easy  to  see  that  the  oxygen 
tension  of  the  air  of  the  pulmonary  alveoli  is  quite  sufficient,  even 
supposing  it  much  less  than  that  of  the  expired  air,  to  enable  the 
venous  blood  to  take  up  oxygen,  and  what  is  more,  it  will  take  it 
up  until  the  haemoglobin  is  very  nearly  saturated  with  the  gas. 

As  regards  the  elimination  of  carbonic  acid  from  the  blood, 
there  is  evidence  to  show  that  it  is  given  up  by  a  process  of  simple 
diffusion,  the  only  condition  necessary  for  the  process  being  that 
the  tension  of  the  carbonic  acid  of  the  air  in  the  pulmonary  alveoli 
should  be  less  than  the  tension  of  the  carbonic  acid  in  venous 
blood.  The  carbonic  acid  tension  of  the  alveolar  air  probably 
does  not  exceed  in  the  dog  3  or  4  per  cent.,  while  that  of  the 
venous  blood  is  5*4  per  cent.,  or  equal  to  41  mm.  of  mercury. 

B.  Respiratory  Changes  in  the  Blood- 
Circulation  of  Blood  in  the  Respiratory  Organs. — To  be 
exposed  to  the  air  thus  alternately  moved  into  and  out  of  the  air 
cells  and  minute  bronchial  tubes,  the  blood  is  propelled  from  the 
right  ventricle  through  the  pulmonary  capillaries  in  steady  streams, 
and  slowly  enough  to  permit  every  minute  portion  of  it  to  be  for 
a  few  seconds  exposed  to  the  air,  with  only  the  thin  walls  of  the 
capillary  vessels  and  the  air-cells  intervening.  The  pulmonary 
circulation  is  of  the  simplest  kind  :  for  the  pulmonary  artery 
branches  regularly ;  its  successive  branches  run  in  straight  lines, 
and  do  not  anastomose  :  the  capillary  plexus  is  uniformly  spread 
over  the  air-cells  and  intercellular  passages  ;  and  the  veins  derived 
from  it  proceed  in  a  course  as  simple  and  uniform  as  that  of  the 
arteries,  their  branches  converging  but  not  anastomosing.  The 
veins  have  no  valves,  or  only  small  imperfect  ones  prolonged  from 
their  angles  of  junction,  and  incapable  of  closing  the  orifice  of 
either  of    the  veins  between  which    they  are  placed.     The  pul- 


chap,  vi.]  VABI0U8    RESPIRATORY    ACTION8, 


245 


monary  circulation  also  is  unaffected  by  changes  of  atmospheric 
pressure,  and  is  not  exposed  to  the  influence  of  tin-  pressur 
muscles  :  the  force  by  which  it  is  accomplished,  and  the  coure 
the  blood  arc  alike  simple. 

Changes  produced  in  the  Blood  by  Respiration. — The 
most  obvious  change  which  the  blood  of  the  pulmonary  artery 
undergoes  in  its  passage  through  the  lungs  is  1st,  that  of  colour. 
the  dark  crimson  of  venous  blood  being  exchanged  for  the  bright 
scarlet  of  arterial  blood;  2nd,  and  in  connection  with  the  pre- 
ceding change,  it  gains  oxygen;  $rd,  it  loses  carbonic  acid;  4^, 
it  becomes  slightly  cooler  (p.  239);  5^,  it  coagulates  sooner 
and  more  firmly,  and,  apparently,  contains  more  fibrin  (see 
p.  108).  The  oxygen  absorbed  into  the  blood  from  the  atmospheric 
air  in  the  lungs  is  combined  chemically  with  the  haemoglobin  of 
the  red  blood-corpuscles.  In  this  condition  it  is  carried  in  the 
arterial  blood  to  the  various  parts  of  the  body,  and  brought  into 
near  relation  or  contact  with  the  tissues.  In  these  tissues,  and  in 
the  blood  which  circulates  in  them,  a  certain  portion  of  the  oxygen, 
which  the  arterial  blood  contains,  disappears,  and  a  proportionate 
quantity  of  carbonic  acid  and  water  is  formed.  The  venous  blood, 
containing  the  new-formed  carbonic  acid  returns  to  the  lungs, 
where  a  portion  of  the  carbonic  acid  is  exhaled,  and  a  fresh  supply 
of  oxygen  is  taken  in. 

Mechanism  of  Various  Respiratory  Actions.— It  will  be 
well  here,  perhaps,  to  explain  some  respiratory  acts,  which  appear 
at  first  sight  somewhat  complicated,  but  cease  to  be  so  when  the 
mechanism  by  which  they  are  performed  is  clearly  understood. 
The  accompanying  diagram  (fig.  161)  shows  that  the  cavity  of  the 
chest  is  separated  from  that  of  the  abdomen  by  the  diaphragm, 
which,  when  acting,  will  lessen  its  curve,  and  thus  descending, 
will  push  downwards  and  forwards  the  abdominal  viscera  ;  while 
the  abdominal  muscles  have  the  opposite  effect,  and  in  acting  will 
push  the  viscera  upwards  and  backwards,  and  with  them  the 
diaphragm,  supposing  its  ascent  to  be  not  from  any  cause  inter- 
fered with.  From  the  same  diagram  it  will  be  seen  that  the  lungs 
communicate  with  the  exterior  of  the  body  through  the  glottis, 
and  further  on  through  the  mouth  and  nostrils — through  either 
of  them  separately,  or  through  both  at  the  same  time,  according 
to  the  position  of  the  soft  palate.      The  stomach  communicates 


246 


RESPIRATION. 


[chap.  vr. 


with  the  exterior  of  the  body  through  the  oesophagus,  pharynx, 
and  mouth ;  while  below  the  rectum  opens  at  the  anus,  and  the 
bladder  through  the  urethra.  All  these  openings,  through  which 
the  hollow  viscera  communicate  with  the  exterior  of  the  body,  are 


Fig.  161. 

guarded  by  muscles,  called  sphincters,  which  can  act  independently 
of  each  other.  The  position  of  the  latter  is  indicated  in  the 
diagram. 

Sighing. — In  sighing  there  is  a  rather  prolonged  inspiration; 
the  air  almost  noiselessly  passing  in  through  the  glottis,  and  by 
the  elastic  recoil  of  the  lungs  and  chest-walls,  and  probably  also  of 
the  abdominal  walls,  being  rather  suddenly  expelled  again. 

Now,  in  the  first,  or  inspiratory  part  of  this  act,  the  descent  of 
the  diaphragm  presses  the  abdominal  viscera   downwards,  and  of 


chap,  vi.]  VARIOUS    RE8PIEATORY    ACTION&  247 

coin^e  tliis  pressure  tends  to  evacuate  the  contents  of  >uch  as 
communicate  with   the  exterior  of  the  body.      Enasmuch,  how- 

r.  as  their  various  openings  are  guarded  by  sphincter  muscl  -. 
in  a  state  of  constant  tonic    contraction,  there  of 

their  contents,  and  air  simply  enters  the  lungs.  In  the  second, 
or  expiratory  part  of  the  act  of  sighing,  there  is  also  pressure 
mode  on  the  abdominal  viscera  in  the  opposite  direction,  by  the 
elastic  or  muscular  recoil  of  the  abdominal  walls  :  but  the  pres- 
sure is  relieved  by  the  escape  of  air  through  the  open  glottis, 
and  the  relaxed  diaphragm  is  pushed  up  again  into  its  original 
position.  The  sphincters  of  the  stomach,  rectum,  and  bladder, 
act  as  before. 

Hiccough  resembles  sighing  in  that  it  is  an  inspiratory  act ; 
but  the  inspiration  is  sudden  instead  of  gradual,  from  the 
diaphragm  acting  suddenly  and  spasmodically  ;  and  the  air.  there- 
fore suddenly  rushing  through  the  unprepared  rima  glottidis, 
causes  vibration  of  the  vocal  cords,  and  the  peculiar  sound. 

Coughing. — In  the  act  of  coughing,  there  is  most  often  first 
an  inspiration,  and  this  is  followed  by  an  expiration  :  but  when 
the  lungs  have  been  tilled  by  the  preliminary  inspiration,  instead 
of  the  air  being  easily  let  out  again  through  the  glottis,  the 
latter  is  momentarily  closed  by  the  approximation  of  the  vocal 
cords,  and  then  the  abdominal  muscles,  strongly  acting,  push  up 
the  viscera  against  the  diaphragm,  and  thus  make  pressure  on  the 
air  in  the  lungs  until  its  tension  is  sufficient  to  burst  open  noisily 
the  vocal  cords  which  oppose  its  outward  passage.  In  this  way  a 
considerable  force  is  exercised,  and  mucus  or  any  other  matter 
that  may  need  expulsion  from  the  lungs  or  trachea  is  quickly  and 
sharply  expelled  by  the  outstreaming  current  of  air. 

Now  it  is  evident  on  reference  to  the  diagram  (fig.  161),  that 
pressure  exercised  by  the  abdominal  muscles  in  the  act  of  cough- 
ing, acts  as  forcibly  on  the  abdominal  viscera  as  on  the  lungs, 
inasmuch  as  the  viscera  form  the  medium  by  which  the  upward 
pressure  on  the  diaphragm  is  made,  and  of  necessity  there  is 
quite  as  great  a  tendency  to  the  expulsion  of  their  contents  as  of 
the  air  in  the  lungs.  The  instinctive,  and  if  necessary,  volun- 
:.ly  increased  contraction  of  the  sphincters,  however,  prevents 
any  escape  at  the  openings  guarded  by  them,  and  the  pressure  is 
effective  at  one  part  only,  namely,  the  rima  glottidis. 


248  RESPIRATION.  [chap.  vi. 

Sneezing. — The  same  remarks  that  apply  to  coughing,  are 
almost  exactly  applicable  to  the  act  of  sneezing ;  but  in  this 
instance  the  blast  of  air,  on  escaping  from  the  lungs,  is  directed, 
by  an  instinctive  contraction  of  the  pillars  of  the  fauces  and 
descent  of  the  soft  palate,  chiefly  through  the  nose,  and  an}- 
offending  matter  is  thence  expelled. 

Speaking. — In  speaking,  there  is  a  voluntary  expulsion  of  air 
through  the  glottis  by  means  of  the  expiratory  muscles ;  and  the 
vocal  cords  are  put,  by  the  muscles  of  the  larynx,  in  a  proper 
position  and  state  of  tension  for  vibrating  as  the  air  passes  over 
them,  and  thus  producing  sound.  The  sound  is  moulded  into 
words  by  the  tongue,  teeth,  lips,  &c. — the  vocal  cords  producing 
the  sound  only,  and  having  nothing  to  do  with  articulation. 

Singing, — Singing  resembles  speaking  in  the  manner  of  its 
production;  the  laryngeal  muscles,  by  variously  altering  the  posi- 
tion and  degree  of  tension  of  the  vocal  cords,  producing  the 
different  notes.  Words  used  in  the  act  of  singing  are  of  course 
framed,  as  in  speaking,  by  the  tongue,  teeth,  lips,  etc. 

Sniffing- — Sniffing  is  produced  by  a  somewhat  quick  action  of 
the  diaphragm  and  other  inspiratory  muscles.  The  mouth  is,  how- 
ever, closed,  and  by  these  means  the  whole  stream  of  air  is  made 
to  enter  by  the  nostrils.  The  alee  nasi  are,  commonly,  at  the 
same  time,  instinctively  dilated. 

Sobbing. — Sobbing  consists  in  a  series  of  convulsive  inspira- 
tions, at  the  moment  of  which  the  glottis  is  usually  more  or  less 
closed. 

Laughing. — Laughing  is  a  series  of  short  and  rapid  expirations. 

Yawning. — Yawning  is  an  act  of  inspiration,  but  is  unlike 
most  of  the  preceding  actions  in  being  always  more  or  less  in- 
voluntary. It  is  attended  by  a  stretching  of  various  muscles 
about  the  palate  and  lower  jaw,  which  is  probably  analogous  to 
the  stretching  of  the  muscles  of  the  limbs  in  which  a  weary 
man  finds  relief,  as  a  voluntary  act,  when  they  have  been  some 
time  out  of  action.  The  involuntary  and  reflex  character  of 
yawning  depends  probably  on  the  fact  that  the  muscles  concerned 
are  themselves  at  all  times  more  or  less  involuntary,  and  require, 
therefore,  something  beyond  the  exercise  of  the  will  to  set  them 
in  action.  For  the  same  reason,  yawning,  like  sneezing,  cannot  be 
well  performed  voluntarily. 


chap,  vi.]  RESPIRATORY    CENTRE,  249 

Sucking. — Slicking  is  not  properly  a  respiratory  act,  but  it 
may  be  most  conveniently  considered  in  tins  place.  It  is  caused 
chiefly  by  the  depressor  muscles  of  the  os  hyoides.  These,  by 
drawing  downwards  and  backwards  the  tongue  and  floor  of  the 
mouth,  produce  a  partial  vacuum  in  the  latter:  and  the  weight  of 
the  atmosphere  then  acting  on  all  sides  tends  to  produce  equili- 
brium on  the  inside  and  outside  of  the  mouth  as  best  it  may. 
The  communication  between  the  mouth  and  pharynx  is  com- 
pletely shut  oft'  by  the  contraction  of  the  pillars  of  the  soft 
palate  and  descent  of  the  latter  so  as  to  touch  the  back  of  the 
tongue  ;  and  the  equilibrium,  therefore,  can  be  restored  only  by 
the  entrance  of  something  through  the  mouth.  The  action, 
indeed,  of  the  tongue  and  floor  of  the  mouth  in  sucking  may  be 
compared  to  that  of  the  piston  in  a  syringe,  and  the  muscles 
which  pull  down  the  os  hyoides  and  tongue,  to  the  power  which 
draws  the  handle. 

Influence  of  the  Nervous  System  in  Respiration. — Like 
all  other  functions  of  the  body,  the  discharge  of  which  is  neces- 
sary to  life,  respiration  must  be  essentially  an  involuntary  act. 
Else,  life  would  be  in  constant  danger,  and  would  cease  on  the 
loss  of  consciousness  for  a  few  moments,  as  in  sleep.  But  it  is 
also  necessary  that  respiration  should  be  to  some  extent  under 
the  control  of  the  will.  For  were  it  not  so,  it  would  be  im- 
possible to  perform  those  voluntary  respiratory  acts  which  have 
been  just  enumerated  and  explained,  as  speaking,  singing,  and  the 
like. 

The  respiratory  movements  and  their  rhythm,  so  far  as  they 
are  involuntary  and  independent  of  consciousness  (as  on  all 
ordinary  occasions)  are  under  the  governance  of  a  nerve-centre 
in  the  medulla  oblongata  corresponding  with  the  origin  of  the 
pneumogastric  nerves ;  that  is  to  say,  the  motor  nerves  and 
through  them,  the  muscles  concerned  in  the  respiratory  move- 
ments, are  excited  by  a  stimulus  which  issues  from  this  part  of 
the  nervous  system.  How  far  the  medulla  acts  automatically,  i.e., 
how  far  the  stimulus  originates  in  it,  or  how  far  it  is  merely  a 
nerve-centre  for  re/lex  action,  is  not  certainly  known.  Probably, 
as  will  be  seen,  both  events  happen;  and,  in  both  cases,  the 
stimulus  is  the  result  of  the  condition  of  the  blood. 

The  respiratory  centre  is  bilateral  or  double,  since  the  respira- 


250  RESPIRATION.  [chap.  vi. 

tory  movements  continue  after  the  medulla  at  this  point  is  divided 
in  the  middle  line. 

As  regards  its  supposed  automatic  action,  it  has  been  shown  that 
if  the  spinal  cord  be  divided  below  the  medulla,  and  both  vagi  be 
divided  so  that  no  afferent  impulses  can  reach  it  from  below,  the 
nasal  and  laryngeal  respiration  continues,  and  the  only  possible 
eourse  of  the  afferent  impulses  would  be  through  the  cranial  nerves  ; 
and  when  the  cord  and  medulla  are  intact  the  division  of  these  pro- 
duces no  effect  upon  respiration,  so  that  it  appears  evident  that  the 
afferent  stimuli  are  not  absolutely  necessary  for  maintaining  the  re- 
spiratory movements.  But  although  automatic  in  its  action  the 
respiratory  centre  may  be  reflexly  excited,  and  the  chief  channel  of 
this  reflex  influence  is  the  vagus  nerve ;  for  when  the  nerve  of  one 
side  is  divided,  respiration  is  slowed,  and  if  both  vagi  be  cut  the 
respiratory  action  is  still  slower. 

The  influence  of  the  vagus  trunk  upon  it  is  twofold,  for  if  the 
nerve  be  divided  below  the  origin  of  the  superior  laryngeal  branch 
and  the  central  end  be  stimulated,  respiratory  movements  are  in- 
creased in  rapidity,  and  indeed  follow  one  another  so  quickly  if 
the  stimuli  be  increased  in  number,  that  after  a  time  cessation 
of  respiration  in  inspiration  follows  from  a  tetanus  of  the  respira- 
tory muscles  (diaphragm).  Whereas  if  the  superior  laryngeal 
branch  be  divided,  although  no  effect,  or  scarcely  any,  follows  the 
mere  division,  on  stimulation  of  the  central  end  respiration  is 
slowed,  and  after  a  time,  if  the  stimulus  be  increased,  stops,  but 
not  in  inspiration  as  in  the  other  case,  but  in  expiration.  Thus 
the  vagus  trunk  contains  fibres  which  slow  and  fibres  which 
accelerate  respiration.  If  we  adopt  the  theory  of  a  doubly  acting 
respiratory  centre  in  the  floor  of  the  medulla,  one  tending  to 
produce  inspiration  and  the  other  expiration,  and  acting  in 
antagonism  as  it  were,  so  that  there  is  a  gradual  increase  in 
the  tendency  to  produce  respiratory  action,  until  it  culminates 
in  an  inspiratory  effort,  which  is  followed  by  a  similar  action 
of  the  expiratory  part  of  the  centre,  producing  an  expiration, 
we  must  look  upon  the  main  trunk  of  the  vagus  as  aiding  the 
inspiratory,  and  of  the  superior  laryngeal  as  aiding  the  expira- 
tory part  of  the  centre,  the  first  nerve  possibly  inhibiting  the 
action  of  the  expiratory  centre,  whilst  it  aids  the  inspiratory,  and 
the  latter  nerve  having  the  very  opposite  effect.     But  inasmuch 


(hap.  vi.]     STIMULATION    OF    RESPIBATORY    CENTER  25 1 

as  the  respiration  is  slowed  on  division  of  the  vagi,  and  not 
quickened  or  affected  manifestly  on  simple  division  of  the  superior 
larygneal,  it  must  be  supposed  that  the  vagi  fibres  are  always  in 
action,  whereas  the  superior  larygneal  fibres  are  not. 

It  appears,  however,  that  there  are.  in  some  animals  at  all 
events,  subordinate  centres  in  the  spinal  cord  which  arc  able, 
under  certain  conditions,  to  discharge  the  function  of  the  chief 
medullary  centre. 

The  centre  in  the  medulla  may  be  influenced  not  only  by 
afferent  impulses  proceeding  along  the  vagus  and  laryngeal  ner 
but  also  by  those  proceeding  from  the  cerebrum,  as  well  as  by 
impressions  made  upon  the  nerves  of  the  skin,  or  upon  part  of 
the  fifth  nerve  distributed  to  the  nasal  mucous  membrane,  or 
upon  other  sensory  nerves,  as  is  exemplified  by  the  deep  inspira- 
tion which  follows  the  application  of  cold  to  the  surface  of  the  skin, 
and  by  the  sneezing  which  follows  the  slightest  irritation  of  the 
nasal  mucous  membrane. 

At  the  time  of  birth,  the  separation  of  the  placenta,  and  the  consequent 
non-oxygenati'on  of  the  foetal  blood,  are  the  circumstances  which  immediately 
lead  to  the  issue  of  automatic  impulses  to  action  from  the  respiratory  centre 
in  the  medulla  oblongata.  But  the  quickened  action  which  ensues  on  the 
application  of  cold  air  or  water,  or  other  sudden  stimulus,  to  the  skin, 
shows  well  the  intimate  connection  which  exists  between  this  centre  and 
other  parts  which  are  not  ordinarily  connected  with  the  function  of 
respiration. 

Methods  of  Stimulation  of  Respiratory  Centre.  —It  is 
now  necessary  to  consider  the  method  by  which  the  centre  or 
centres  are  stimulated  themselves,  as  well  as  the  manner,  in 
which  the  afferent  vagi  impulses  are  produced. 

The  more  venous  the  blood,  the  more  marked  are  the  inspira- 
tory impulses,  and  if  the  air  is  prevented  from  entering  the  che 
in  a  short  time  the  respiration  becomes  very  laboured.  Its  cessation 
is  followed  by  an  abnormal  rapidity  of  the  inspiratory  acts,  which 
make  up  even  in  depth  for  the  previous  stoppage.  The  condition 
caused  by  obstruction  to  the  entrance  of  air,  or  by  any  circum- 
stance by  which  the  oxygen  of  the  blood  is  used  up  in  an  abnor- 
mally quick  manner,  is  known  as  dyspnoea^  and  as  the  aeration  of 
the  blood  becomes  more  and  more  interfered  with,  not  only  are 
the  ordinary  respiratory  muscles  employed,  but  also  those  extraor- 


252  RESPIBATIONi  [cbap.  vl 

dinary  muscles  which  have  been  previously  enumerated  (p.  231), 
so  that  as  the  blood  becomes  more  and  more  venous  the  action  of 
the  medullary  centre  becomes  mure  and  more  active.  The  ques- 
tion arises  as  to  what  condition  of  the  venous  blood  causes  this 
increased  activity,  whether  it  is  due  to  deficiency  of  oxygen  or 
excess  of  carbonic  acid  in  the  blood.  This  has  been  answered  by 
the  experiments,  which  show  on  #the  one  hand  that  dyspnoea 
occurs  when  there  is  no  obstruction  to  the  exit  of  carbonic  acid, 
as  when  an  animal  is  placed  in  an  atmosphere  of  nitrogen,  and 
therefore  cannot  be  due  to  the  accumulation  of  carbonic  acid,  and 
secondly,  that  if  plenty  of  oxygen  be  supplied,  dyspnoea  proper  does 
not  occur,  although  the  carbonic  acid  of  the  blood  is  in  excess. 
The  respiratory  centre  is  evidently  stimulated  to  action  by  the 
absence  of  sufficient  oxygen  in  the  blood  circulating  in  it. 

The  method  by  which  the  vagus  is  stimulated  to  conduct  afferent 
impulses,  influencing  the  action  of  the  respiratory  centre,  appears 
to  be  by  the  venous  blood  circulating  in  the  lungs,  or  as  some  say 
by  the  condition  of  the  air*  in  the  pulmonary  alveoli.  And  if 
either  of  these  be  the  stimuli  it  will  be  evident  that  as  the 
condition  of  venous  blood  stimulates  the  peripheral  endings  of  the 
vagus  in  the  lungs,  the  vagus  action  which  tends  to  help  on  the 
discharge  of  inspirator}'  impulses  from  the  centre,  must  tend  also  to 
increase  the  activity  of  the  centre,  when  the  blood  in  the  lungs 
becomes  more  and  more  venous.  Xo  doubt  the  venous  condition 
of  the  blood  will  affect  all  the  sensory  nerves  in  a  similar  manner, 
but  it  has  been  shown  that  the  circulation  of  too  little  blood 
through  the  centre  is  quite  sufhcient  by  itself  for  the  purpose ;  as 
when  its  blood  supply  is  cut  off  increased  inspiratory  actions 
ensue. 

Effects  of  Vitiated  Air.— Ventilation. — We  have  seen  that 
the  air  expired  from  the  lungs  contains  a  large  proportion  of 
carbonic  acid  and  a  minute  amount  of  organic  putrescible  matter. 

Hence  it  is  obvious  that  if  the  same  air  be  breathed  again  and 
again,  the  proportion  of  carbonic  acid  and  organic  matter  will 
constantly  increase  till  fatal  results  are  produced ;  but  long 
before  this  point  is  reached,  uneasy  sensations  occur,  such  as 
headache,  languor,  and  a  sense  of  oppression.  It  is  a  remarkable 
fact  that  the  organism  after  a  time  adapts  itself  to  such  a  vitiated 
atmosphere,  and  that  a  person  soon   comes  to  breathe,  without 


CHAP,  vi.]  EFFECT    ON    THE    CIBCULATION.  253 

sensible  inconvenience,  an  atmosphere  which,  when  he  Brsi  entered 
it,  felt  intolerable.  Such  an  adaptation,  however,  can  only  take 
place  at  the  expense  of  &  depression  of  all  the  vital  functions, 
which  must  be  injurious  if  long  continued  or  often  repeated. 

This  power  nf  adaptation  is  well  illustrated  bj  the  experiments  of  Claude 
Bernard.    A  sparrow  is  placed  under  a  bell-glass  of  such  a  size  that  it  will 

live  for  three  hours.  If  now  at  Hie  end  of  the  second  hour  (when  it  could 
have  survived  another  hour)  it  be  taken  out  and  a  fresh  healthy  sparrow 
introduced,  the  latter  will  perish  instantly. 

The  adaptation  above  spoken  of  is  a  gradual  and  eontinuous  one  :  thus  a 
bird  which  will  live  one  hour  in  a  pint  of  air  will  live  three  hours  in  two 
pints;  and  if  two  birds  of  the  same  species,  age,  and  size,  be  placed  in  a 
quantity  of  air  in  which  either,  separately,  Avould  survive  three  hours,  they 
will  not  live  ih  hour,  but  only  i\  hour. 

From  what  has  been  said  it  must  be  evident  that  provision  for 
a  constant  and  plentiful  supply  of  fresh  air,  and  the  removal  of 
that  which  is  vitiated,  is  of  far  greater  importance  than  the  actual 
cubic  space  per  head  of  occupants.  Not  less  than  2000  cubic 
feet  per  head  should  be  allowed  in  sleeping  apartments  (barracks, 
hospitals,  itc),  and  with  this  allowance  the  air  can  only  be  main- 
tained at  the  proper  standard  of  purity  by  such  a  system  of  venti- 
lation as  provides  for  the  supply  of  1500  to  2000  cubic  feet  of 
fresh  air  per  head  per  hour.     (Parkes.) 

The  Effect  of  Respiration  on  the  Circulation. 

Inasmuch  as  the  hgart  and  great  vessels  are  situated  in  the 
air-tight  thorax,  they  are  exposed  to  a  certain  alteration  of  pres- 
sure when  the  capacity  of  the  latter  is  increased  ;  for  although  the 
expansion  of  the  lungs  during  inspiration  tends  to  counter-balance 
this  increase  of  area,  it  never  quite  does  so,  since  part  of  the  pres- 
sure of  the  air  which  is  drawn  into  the  chest  through  the  trachea 
is  expended  in  overcoming  the  elasticity  of  the  lungs  themselves. 
The  amount  thus  used  up  increases  as  the  lungs  become  more 
and  more  expanded,  so  that  the  pressure  inside  the  thorax  during 
inspiration  as  far  as  the  heart  and  great  vessels  are  concerned,  never 
quite  equals  that  outside,  and  at  the  conclusion  of  inspiration  is  con- 
siderably less  than  the  atmospheric  pressure.  It  has  been  ascer- 
tained that  the  amount  of  the  pressure  used  up  in  the  way  above 
described,  varies  from  5  or  7  mm.  of  mercury  during  the  pause,  and 


254 


RESPIRATION. 


[chap.  vr. 


to  30  mm.  of  mercury  when  the  lungs  are  expanded  at  the  end  of  a 
deep  inspiration,  so  that  it  will  be  understood  that  the  pressure  to 
which  the  heart  and  great  vessels  are  subjected  diminishes  as 
inspiration  progresses.  It  will  be  understood  from  the  accom- 
panying diagram  how,  if  there  were  no  lungs  in  the  chest,  but 


Fig.  162.— Diagram  of  an  apparatus  illustrating  the  effect  of  inspiration  upon  the  heart  and 
great  vessete  within  the  thorax.— I,  the  thorax  at  rest ;  II,  during  inspiration  ;  d,  repre- 
sents the  diaphragm  when  relaxed  ;  d'  when  contracted  (it  must  be  remembered  that 
this  position  is  a  mere  diagram),  i.e.,  when  the  capacity  of  the  thorax  is  enlarged: 
h,  the  heart ;  v,  the  veins  entering  it,  and  a,  the  aorta ;  a?,  U,  the  right  and  left 
lung;  t,  the  trachea;  m,  mercurial  manometer  in  connection  with  the  pleura  The 
increase  in  the  capacity  of  the  box  representing  the  thorax  is  seen  to  dilate  the  heart 
as  well  as  the  lungs,  and  so  to  pump  in  blood  through  v,  whereas  the  valve  prevents 
reflex  through  a.  The  position  of  the  mercury  in  m  shows  also  the  suction  which  is 
taking  place.     (Landois.) 

if  its  capacity  were  increased,  the  effect  of  the  increase  would 
be  expended  in  pumping  blood  into  the  heart  from  the  veins,  but 
even  with  the  lungs  placed  as  they  are,  during  inspiration  the 
pressure  outside  the  heart  and  great  vessels  is  diminished,  and 
they  have  therefore  a  tendency  to  expand  and  to  diminish  the 
intra-vascular  pressure.     The  diminution  of  pressure  within  the 


chap,  vi.]  1 . 1  1  1 :«  T    ON    tin:    <  [BCULATION. 


255 


veins  passing  to  the  right  auricle  and  within  the  right  auricle 
itself,  will  draw  the  blood  into  the  thorax,  and  bo  assist  the  circu- 
lation :    this   suction   action   aiding,   though    independently,   the 

suction  power  of  the  diastole  of  the  auricle  about  which  we  have 
previously  spoken  (p.  153)-  The  effect  of  sucking  more  blood  into 
the  right  auricle  will,  caterif  paribus  increase  the  amount  passing 

through  the  right  ventricle,  which  also  exerts  a  similar  suction 
action,  and  through  the  lungs  into  the  left  auricle  and  ventricle 
and  thus  into  the  aorta,  and  this  tends  to  increase  the  arterial 
tension.  The  effect  of  the  diminished  pressure  upon  the  pul- 
monary vessels  will  also  help  towards  the  same  end,  i.e.,  an 
increased  flow  through  the  lungs,  so  that  as  far  as  the  heart 
and  its  veins  are  concerned  inspiration  increases  the  blood 
pressure  in  the  arteries.  The  effect  of  inspiration  upon  the 
aorta  and  its  branches  within  the  thorax  would  be,  however, 
contrary ;  for  as  the  pressure  outside  is  diminished  the  vessels- 
would  tend  to  expand,  and  thus  to  diminish  the  tension  of  the 
blood  within  them,  but  inasmuch  as  the  large  arteries  are  capable 
of  little  expansion  beyond  their  natural  calibre,  the  diminution  of 
the  arterial  tension  caused  by  this  means  would  be  insufficient  to 
counteract  the  increase  of  arterial  tension  produced  by  the  effect 
of  inspiration  upon  the  veins  of  the  chest,  and  the  balance  of  the 
whole  action  would  be  in  favour  of  an  increase  of  arterial  tension 
during  the  inspiratoiy  period.  But  if  a  tracing  of  the  variation 
be  taken  at  the  same  time  that  the  respiratory  movements  are 
recorded,  it  will  be  found  that,  although  speaking  generally,  the 
arterial  tension  is  increased  during  inspiration,  the  maximum  of 
arterial  tension  does  not  correspond  with  the  acme  of  inspira- 
tion (fig.  163). 

As  regards  the  effect  of  expiration,  the  capacity  of  the  chest  is 
diminished,  and  the  intra-thoracic  pressure  returns  to  the  normal, 
which  is  not  exactly  equal  to  the  atmospheric,  pressure.  The 
effect  of  this  011  the  veins  is  to  increase  their  intra-vascular  pres- 
sure, and  so  to  diminish  the  flow  of  blood  into  the  left  side  of 
the  heart,  and  with  it  the  arterial  tension,  but  this  is  almost 
exactly  balanced  by  the  necessary  increase  of  arterial  tension 
caused  by  the  increase  of  the  extra-vascular  pressure  of  the  aorta 
and  large  arteries,  so  that  the  arterial  tension  is  not  much 
affected  during  expiration  either  way.      Thus,  ordinary  expiration 


256  RESPIRATION.  [chap.  vi. 

does  not  produce  a  distinct  obstruction  to  the  circulation,  as  even 
when  the  expiration  is  at  an  end  the  intra-thoracic  pressure  is  less 
than  the  extra-thoracic. 


/ 


Pig.  163. — Comparison  of  blood-pressure  curve  with  curve  of  intra-thoracic  pressure.  [To  be 
read  from  left  to  right.)  a  is  the  curve  of  blood-pressure  •with  its  respiratory  undula- 
tions, the  slower  beats  on  the  descent  being  very  marked  ;  b  is  the  curve  of  intra- 
thoracic pressure  obtained  by  connecting  one  limb  of  a  manometer  with  the  pleural 
cavity.  Inspiration  begins  at  i  and  expiration  at  c.  The  intra-thoracic  pressure  rises 
very  rapidly  after  the  cessation  of  the  inspiratory  effort,  and  then  slowly  falls  as  the 
air  issues  from  the  chest ;  at  the  beginning  of  the  inspiratory  effort  the  fall  becomes 
more  rapid .     ( M .  Foster . ) 

The  effect  of  violent  expiratory  efforts,  however,  has  a  distinct 
action  in  preventing  the  current  of  blood  through  the  lungs,  as  seen 
in  the  blueness  of  the  face  from  congestion  in  straining ;  this  con- 
dition being  produced  by  pressure  on  the  small  pulmonary  vessels. 

We  may  summarise  this  mechanical  effect  therefore,  and  say 
that  inspiration  aids  the  circulation  and  so  increases  the  arterial 
tension,  and  that  although  expiration  does  not  materially  aid  the 
circulation,  yet  under  ordinary  conditions  neither  does  it  obstruct. 
Under  extraordinary  conditions,  as  in  violent  expirations,  the 
circulation  is  decidedly  obstructed.  But  we  have  seen  that  there 
is  no  exact  correspondence  between  the  points  of  extreme  arterial 
tension  and  the  end  of  inspiration,  and  we  must  look  to  the  nervous 
system  for  an  explanation  of  this  apparently  contradictory  result. 

The  effect  of  the  nervous  system  in  producing  a  rhythmical 
alteration  of  the  blood  pressure  is  two-fold.  In  the  first  place  the 
cardio-inhibitory  centre  is  believed  to  be  stimulated  during  the 
fall  of  blood  pressure,  producing  a  slower  rate  of  heart-beats 
during  expiration,  which  will  be  noticed  in  the  tracing  (fig.  163), 


CHAP.   VI.] 


TEATJBE-HERING'S    CUEVES. 


257 


the  undulations  during  the  decline  of  blood-pressure  being  l< 
but  less  frequent     This  effect  disappears  when,  by  sectioD  of  the 
vagi,  the  effect  of  the  centre  is  cut  off  from  the  heart.     In  the 


Fig1.  164. — Traube-Hering's  curves.  (To  be  read  from  left  to  right.)  The  curves  1,  2,  3,  4, 
and  5  are  portions  selected  from  one  continuous  tracing  forming  the  record  of  a 
prolonged  observation,  so  that  the  several  curves  represent  successive  stages  of  the 
same  experiment.  Each  curve  is  placed  in  its  proper  position  relative  to  the  base  line, 
which  is  omitted ;  the  blood-pressure  rises  in  stages  from  1,  to  2,  3,  and  4,  but  falls 
again  in  stage  5.  Curve  1  is  taken  from  a  period  when  artificial  respiration  was  being- 
kept  up,  but  the  vagi  having  been  divided,  the  pidsations  on  the  ascent  and  descent  of 
the  undulations  do  not  differ ;  when  artificial  respiration  ceased  these  undulations  for  a 
while  disappeared,  and  the  blood-pressure  rose  steadily  while  the  heart-beats  became 
slower.  Soon,  as  at  2,  new  undulations  appeared  ;  a  little  later,  the  blood-pressure  was 
still  rising,  the  heart-beats  still  slower,  but  the  undulations  still  more  obvious  (3 )  ; 
still  later  (4},  the  pressure  was  still  higher,  but  the  heart-beats  were  quicker,  and  the 
undulations  flatter,  the  pressure  then  began  to  fall  rapidly  (5),  and  continued  to  fall 
until  some  time  after  artificial  respiration  was  resumed.    (M.  Foster.) 


second  place,  the  vaso-motor  centre  is  also  believed  to  send  out 
rhythmical  impulses,  by  which  undulations  of  blood  pressure  are 
produced  independently  of  the  mechanical  effects  of  respiration. 
The  action  of  the  vaso-motor  centre  in  taking  part  in   pro- 

s 


258  RESPIRATION.  [chap.  vi. 

during  rhythmical  changes  of  blood-pressure  which  are  called 
respiratory,  is  shown  in  the  following  way  : — In  an  animal  under 
the  influence  of  urari,  a  record  of  whose  blood-pressure  is  being 
taken,  and  where  artificial  respiration  has  been  stopped,  and  both 
vagi  cut,  the  blood-pressure  curve  rises  at  first  almost  in  a  straight 
line ;  but  after  a  time  new  rhythmical  undulations  occur  very  like 
the  original  respiratory  undulations,  only  somewhat  larger.  These 
are  called  Traube's  or  Travbe-Herinefs  curves.  They  continue 
whilst  the  blood-pressure  continues  to  rise,  and  only  cease  when 
the  vaso-motor  centre  and  the  heart  are  exhausted,  when  the 
pressure  speedily  falls.  These  curves  must  be  dependent  upon 
the  vaso-motor  centre,  as  the  mechanical  effects  of  respiration 
have  been  eliminated  by  the  poison  and  by  the  cessation  of  artifi- 
cial respiration,  and  the  effect  of  the  cardio-inhibitory  centre  be 
the  division  of  the  vagi.  It  may  be  presumed  therefore  that  the 
vaso-motor  centre,  as  well  as  the  cardio-inhibitory,  must  be  con- 
sidered to  take  part  with  the  mechanical  changes  of  inspiration 
and  expiration  in  producing  the  so-called  respiratory  undulations 
<  «f  blood-pressure. 

Cheyne-Stohes'  breathing. — This  is  a  rhythmical  irregularity  in  respira- 
tions -which  has  been  observed  in  various  diseases,  and  is  especially  connected 
with  fatty  degeneration  of  the  heart.  Respirations  occur  in  groups,  at  the 
beginning  of  each  group  the  inspirations  are  very  shallow,  but  each  succes- 
sive breath  is  deeper  than  the  preceding  until  a  climax  is  reached,  then 
comes  in  a  prolonged  sighing  expiration,  succeeded  by  a  pause,  after  which 
the  next  group  begins. 

Apncea.— Dyspnoea.— Asphyxia. 

As  blood  which  contains  a  normal  proportion  of  oxygen  excites 
the  respiratory  centre  (p.  252),  and,  as  the  excitement  and  conse- 
quent respiratory  muscular  movements  are  greater  (dyspnoea)  in 
proportion  to  the  deficiency  of  this  gas,  so  an  abnormally  large 
proportion  of  oxygen  in  the  blood  leads  to  diminished  breathing 
movements,  and,  if  the  proportion  be  large  enough,  to  their  tem- 
porary cessation.  This  condition  of  absence  of  breathing  is  termed 
apnoea*  and  it  can  be  demonstrated,  in  one  of  the  lower  animals, 

*  This  term  has  been,  unfortunately,  often  applied  to  conditions  of 
dyspnoea  or  asphyxia  ;  but  the  modern  application  of  the  term,  as  in  the 
text,  is  the  more  convenient. 


CHAP,  vi.]  ASPHYXIA.  259 

by  performing  artificial  respiration  to  the  extent  of  saturating  the 
Mood  with  oxygen. 

When,  on  the  other  hand,  the  respiration  is  stopped,  by,  e.g., 

interference  with  the  passage  of  air  to  the  lungs,  or  by  supplying 
aii-  devoid  of  oxygen,  a  condition  ensues,  which  passes  rapidly 
from  the  state  of  dyspnoea  (difficult  breathing)  to  what  is  termed 
asphyxia  ;  and  the  latter  quickly  ends  in  death. 

The  ways  by  which  this  condition  of  asphyxia  may  be  produced 
are  very  numerous ;  as,  for  example,  by  the  prevention  of  the 
due  entry  of  oxygen  into  the  blood,  either  by  direct  obstruction  of 
the  trachea  or  other  part  of  the  respiratory  passages,  or  by  intro- 
ducing instead  of  ordinary  air  a  gas  devoid  of  oxygen,  or,  again, 
by  interference  with  the  due  interchange  of  gases  between  the 
air  and  the  blood. 

Symptoms  of  Asphyxia. — The  most  evident  symptoms  of 
asphyxia  or  suffocation  are  well  known.  Violent  action  of  the 
respiratory  muscles  and,  more  or  less,  of  all  the  muscles  of  the 
body ;  lividity  of  the  skin  and  all  other  vascular  parts,  while  the 
veins  are  also  distended,  and  the  tissues  seem  generally  gorged 
with  blood ;  convulsions,  quickly  followed  by  insensibility,  and 
death. 

The  conditions  which  accompany  these  symptoms  are — 

(1)  More  or  less  interference  with  the  passage  of  the  blood 
through  the  pulmonary  blood-vessels. 

(2)  Accumulation  of  blood  in  the  right  side  of  the  heart  and  in 
the  systemic  veins. 

(3)  Circulation  of  impure  (non-aerated)  blood  in  all  parts  of  the 
body. 

Cause  of  Death  from  Asphyxia. — The  causes  of  these 
conditions  and  the  manner  in  which  they  act,  so  as  to  be  incom- 
patible with  life,  may  be  here  briefly  considered. 

(1)  The  obstruction  to  the  passage  of  blood  through  the  lungs 
is  not  so  great  as  it  was  once  supposed  to  be  ;  and  such  as  there 
is  occurs  chiefly  in  the  later  stages  of  asphyxia,  when,  by  the 
violent  and  convulsive  action  of  the  expiratory  muscles,  pressure 
is  indirectly  made  on  the  lungs,  and  the  circulation  through  them 
is  proportionately  interfered  with. 

(2)  Accumulation  of  blood,  with  consequent  distension  of  the 
right  side  of  the  heart  and  systemic  veins,  is  the  direct  result,  at 

s  2 


26o  RESPIRATION.  [chap.  vi. 

least  in  part,  of  the  obstruction  to  the  pulmonary  circulation  just 
referred  to.  Other  causes,  however,  are  in  operation,  (a)  The 
vaso-motor  centres  stimulated  by  blood  deficient  in  oxygen, 
causes  contraction  of  all  the  small  arteries  with  increase  of  arterial 
tension,  and  as  an  immediate  consequence  the  filling  of  the 
systemic  veins.  (6)  The  increased  arterial  tension  is  followed  by 
inhibition  of  the  action  of  the  heart,  and,  thus,  the  latter,  con- 
tracting less  frequently,  and  gradually  enfeebled  also  by  deficient 
supply  of  oxygen,  becomes  over-distended  by  blood  which  it  cannot 
expel.  At  this  stage  the  left  as  well  as  the  right  cavities  are 
distended  with  blood. 

The  ill  effects  of  these  conditions  are  to  be  looked  for  partly  in 
the  heart,  the  muscular  fibres  of  which,  like  those  of  the  urinary 
bladder  or  any  other  hollow  muscular  organ,  may  be  paralysed 
by  over-stretching ;  and  partly  in  the  venous  congestion,  and 
consequent  interference  with  the  function  of  the  higher  nerve- 
centres,  especially  the  medulla  oblongata. 

(3)  The  passage  of  non-aerated  blood  through  the  lungs  and 
its  distribution  over  the  body  are  events  incompatible  with  life, 
in  one  of  the  higher  animals,  for  more  than  a  few  minutes ; 
the  rapidity  with  which  death  ensues  in  asphyxia  being  due, 
more  particularly,  to  the  effect  of  non-oxygenized  blood  on  the 
medulla  oblongata,  and,  through  the  coronary  arteries,  on  the 
muscular  substance  of  the  heart.  The  excitability  of  both 
nervous  and  muscular  tissue  is  dependent  on  a  constant  and 
large  supply  of  oxygen,  and,  when  this  is  interfered  with,  is 
rapidly  lost.  The  diminution  of  oxygen,  it  may  be  here  remarked, 
has  a  more  direct  influence  in  the  production  of  the  usual  symp- 
toms of  asphyxia  than  the  increased  amount  of  carbonic  acid. 
Indeed,  the  fatal  effect  of  a  gradual  accumulation  of  the  latter  in 
the  blood,  if  a  due  supply  of  oxygen  be  maintained,  resembles 
rather  that  of  a  narcotic  poison. 

In  some  experiments  performed  by  a  committee  appointed  by  the  Medico- 
Chirurgical  Society  to  investigate  the  subject  of  Suspended  Animation,  it 
was  found  that,  in  the  dog,  during  simple  asphyxia.  i.e.t  by  simple  privation 
of  air,  as  by  plugging  the  trachea,  the  average  duration  of  the  respiratory 
movements  after  the  animal  had  been  deprived  of  air,  was  4  minutes  5 
seconds ;  the  extremes  being  3  minutes  30  seconds,  and  4  minutes  40 
seconds.  The  average  duration  of  the  heart's  action,  on  the  other  hand, 
was  7  minutes  1 1  seconds  :  the  extremes  being  6  minutes  40  seconds,  and 


chap.  vi. J  ASPHYXIA.  2(3! 

7  minutes  45  seconds.  It  would  Beem,  therefore,  that  on  an  average,  the 
heart's  action  continues  for  3  minutes  15  seconds  after  the  animal  has  cea 

make  respiratory  efforts.     A   very  similar  relation  was  observed  in  the 
rabbit     Recovery  never  took  place  after  the  heart's  action  had  ceased. 

The  results  obtained  by  the  committee  on  the  subject  of  drowning  were 
very  remarkable,  especially  in  this  respect,  that  whereas  an  animal  mav 
recover,  after  simple  deprivation  of  air  for  nearly  four  minutes,  yet,  after 
submersion  in  water  for  1$  minute,  recov  \a  to  be  impossible.     This 

remarkable  difference  was  found  to  be  due.  not  to  the  mere  submersion,  nor 
directly  to  the  si  E  the  animal,  nor  to  depression  of  temperature,  but 

t  1  the  two  facts,  that  in  drowning,  a  free  passage  is  allowed  to  air  out  of  the 
lungs,  and  a  free  entrance  of  water  into  them.  It  is  probably  to  the  entrance 
<>f  water  into  the  lungs  that  the  speedy  death  in  drowning  is  mainly  due. 
The  results  of  post-mortem  examination  strongly  support  this  view.  On 
examining  the  lungs  of  animals  deprived  of  air  by  plugging  the  trachea, 
they  were  found  simply  congested  ;  but  in  the  animals  drowned,  not  only 
was  the  congestion  much  more  intense,  accompanied  with  ecchymosed  points 
on  the  surface  and  in  the  substance  of  the  lung,  but  the  air  tubes  were  com- 
pletely choked  up  with  a  sanious  foam,  consisting  of  blood,  water,  and 
mucus,  churned  up  with  the  air  in  the  lungs  by  the  respiratory  efforts  of  the 
animal.  The  lung-substance,  too.  appeared  to  be  saturated  and  sodden  with 
water,  which,  stained  slightly  with  blood,  poured  out  at  any  point  where  a 
section  was  made.  The  lung  thus  sodden  with  water  was  heavy  (though  it 
floated),  doughy,  pitted  on  pressure,  and  was  incapable  of  collapsing.  It  is 
not  difficult  to  understand  how.  by  such  infarction  of  the  tubes,  air  is  de- 
barred from  reaching  the  pulmonary  cells  :  indeed  the  inability  of  the  lungs 
to  collapse  on  opening  the  chest  is  a  proof  of  the  obstruction  which  the  froth 
occupying  the  air-tubes  offers  to  the  transit  of  air. 

We  must  carefully  distinguish  the  asphyxiating  effect  of  an 
insufficient  supply  of  oxygen  from  the  directly  poisonous  action  of 
such  a  gas  as  carbonic  oxide,  which  is  present  to  a  considerable 
amount  in  common  coal-gas.  The  fatal  effects  often  produced  by 
this  gas  (as  in  accidents  from  burning  charcoal  stoves  in  small 
close  rooms),  are  due  to  its  entering  into  combination  with  the 
haemoglobin  of  the  blood-corpuscles  (p.  117),  and  thus  expelling 
the  oxygen. 


262 


FOOD. 


[CHAP.  VII. 


CHAPTER  VII. 


FOOD. 

In  order  that  life  may  be  maintained  it  is  necessary  that  the 
body  should  be  supplied  with  food  in  proper  quality  and  quantity. 

The  food  taken  in  by  the  animal  body  is  used  for  the  purpose  of 
replacing  the  waste  of  the  tissues.  And  to  arrive  at  a  reasonable 
estimation  of  the  proper  diet  in  twenty-four  hours  it  is  necessary  to 
consider  the  amount  of  the  excreta  daily  eliminated  from  the  body. 
The  excreta  contain  chiefly  carbon,  hydrogen,  oxygen,  and  nitro- 
gen, but  also  to  a  less  extent,  sulphur,  phosphorus,  chlorine, 
potassium,  sodium,  and  certain  other  of  the  elements.  Since  this 
is  the  case  it  must  be  evident  that,  to  balance  this  waste,  foods 
must  be  supplied  containing  all  these  elements  to  a  certain 
degree,  and  some  of  them,  viz.,  those  which  take  the  principal  part 
in  forming  the  excreta,  in  large  amount.  We  have  seen  in  the 
last  Chapter  that  carbonic  acid  and  ammonia,  i.e.,  the  elements 
carbon,  oxygen,  nitrogen,  hydrogen,  are  given  off  from  the  lungs. 
By  the  excretion  of  the  kidneys — the  urine — many  elements  are 
discharged  from  the  blood,  especially  nitrogen,  hydrogen,  and 
oxygen.  In  the  sweat,  the  elements  chiefly  represented  are 
carbon,  hydrogen,  and  oxygen,  and  also  in  the  feces.  By  all  the 
excretions  large  quantities  of  water  are  got  rid  of  daily,  but 
chiefly  by  the  urine. 

The  relations  between  the  amounts  of  the  chief  elements  con- 
tained in  these  various  excreta  in  twenty-four  hours  may  be 
represented  in  the  following  way  (Landois)  : 


Water. 

C. 

H. 

N. 

0. 

By  the  lungs    .     . 
By  the  skin      .     . 
By  the  urine    .     . 
By  the  faeces    .    . 

330 

660 

1700 

128 

248-8 
2'6 

9-8 

20* 

3  3 

3' 

1 

is-8 
3' 

651-15 

7-2 

III 

12" 

Grammes  .     . 

2818 

28r2 

&s            188 

68r4I 

CHAP.  VII.]  CLASSIFICATION.  26$ 

To  this  should  be  added  296-  grammes  water,  which  are  produced 
by  the  union  of  hydrogen  and  oxygen  in  the  body  during  the 
process  of  oxydation  (i.e.,  32*89  hydrogen  and  263-41  oxygen). 
There  are  twenty-six  grammes  of  salts  got  rid  of  by  the  urine  and 
six  by  the  faxes.  As  the  water  can  be  supplied  as  such,  the  losses  of 
carbon,  nitrogen,  and  oxygen  are  those  to  which  we  should  direct 
our  attention  in  supplying  food. 

For  the  sake  of  example,  we  may  now  take  only  two  elements, 
carbon  and  nitrogen,  and,  if  we  discover  what  amount  of  these  is 
respectively  discharged  in  a  given  time  from  the  body,  we  shall  be 
in  a  position  to  judge  what  kind  of  food  will  most  readily  and 
economically  replace  their  loss. 

The  quantity  of  carbon  daily  lost  from  the  body  amounts  to 
about  281*2  grammes  or  nearly  4,500  grains,  and  of  nitrogen 
1 8 -8  grammes  or  nearly  300  grains  ;  and  if  a  man  could  be  fed 
by  these  elements,  as  such,  the  problem  would  be  a  very  simple 
one  ;  a  corresponding  weight  of  charcoal,  and,  allowing  for  the 
oxygen  in  it,  of  atmospheric  air,  would  be  all  that  is  necessary. 
But  an  animal  can  live  only  upon  these  elements  when  they  are 
arranged  in  a  particular  manner  with  others,  in  the  form  of  an 
organic  compound,  as  albumen,  starch,  and  the  like;  and  the 
relative  proportion  of  carbon  to  nitrogen  in  either  of  these  com- 
pounds alone,  is,  by  no  means,  the  proportion  required  in  the  diet 
of  man.  Thus,  in  albumen,  the  proportion  of  carbon  to  nitrogen 
is  only  as  3-5  to  1.  If,  therefore,  a  man  took  into  his  body,  as 
food,  sufficient  albumen  to  supply  him  with  the  needful  amount 
of  carbon,  he  would  receive  more  than  four  times  as  much  nitrogen 
as  he  wanted ;  and  if  he  took  only  sufficient  to  supply  him  with 
nitrogen,  he  would  be  starved  for  want  of  carbon.  It  is  plain, 
therefore,  that  he  should  take  with  the  albuminous  part  of  his 
food,  which  contains  so  large  a  relative  amount  of  nitrogen  in 
proportion  to  the  carbon  he  needs,  substances  in  which  the 
nitrogen  exists  in  much  smaller  quantities  relatively  to  the 
carbon. 

It  is  therefore  evident  that  the  diet  must  consist  of  several 
substances,  not  of  one  alone,  and  we  must  therefore  turn  to  the 
available  food-stuffs.  For  the  sake  of  convenience  they  may  be 
classified  as  follows  : 


264  FOOD.  [chap.  vii. 

A.  ORGANIC. 

I.  Nitrogenous,  consisting  of  Proteids,  e.g.  albumen,  casein,  syntonin, 

gluten,  legumin  and  their  allies  ;  and  Gelatins,  which  include  gela- 
tin, elastin,  and  chondrin.  All  of  these  contain  carbon,  hydrogen, 
oxygen,  and  nitrogen,  and  some  in  addition,  phosphorus  and 
sulphur. 

II.  Non-Nitrogenous,  comprising  : 

(1.)  Amyloid  or  saccharine  bodies,  chemically  known  as  carbo-hydrates, 
since  they  contain  carbon,  hydrogen,  and  oxygen,  with  the  last 
two  elements  in  the  proportion  to  form  water,  i.e..  H2  0.  To 
this  class  belong  starch  and  sugar. 

(2.)  Oils  and  fats. — These  contain  carbon,  hydrogen,  and  oxygen;  but 
the  oxygen  is  less  in  amount  than  in  the  amyloids  and  saccharine 
bodies. 

B.  INORGANIC. 

L  Mineral  and  saline  matter. 
II.  Water. 

To  supply  the  loss  of  nitrogen  and  carbon,  it  is  found  by  expe- 
rience that  it  is  necessaiy  to  combine  substances  which  contain 
:i  large  amount  of  nitrogen  with  others  in  which  carbon  is  in 
considerable  amount ;  and  although,  without  doubt,  if  it  were 
possible  to  relish  and  digest  one  or  other  of  the  above-mentioned 
proteids  when  combined  with  a  due  quantity  of  an  amyloid  to 
supply  the  carbon,  such  a  diet,  together  with  salt  and  water, 
ought  to  support  life ;  yet  we  find  that  for  the  purposes  of  ordi- 
nary life  this  system  does  not  answer,  and  instead  of  confining  our 
nitrogenous  foods  to  one  variety  of  substance  we  obtain  it  in  a 
large  number  of  allied  substances,  for  example,  in  flesh,  of  bird, 
beast,  or  fish ;  in  eggs  ;  in  milk  ;  and  in  vegetables.  And,  again, 
we  are  not  content  with  one  kind  of  material  to  supply  the  carbon 
necessary  for  maintaining  life,  but  seek  more,  in  bread,  in  fats,  in 
vegetables,  in  fruits.  Again,  the  fluid  diet  is  seldom  supplied  in 
the  form  of  pure  water,  but  in  beer,  in  wines,  in  tea  and  coffee,  as 
well  as  in  fruits  and  succulent  vegetables. 

Man  requires  that  his  food  should  be  cooked.  Very  few  organic 
substances  can  be  properly  digested  without  previous  exposure  to 
heat  and  to  other  manipulations  which  constitute  the  process  of 
cooking.  It  will  be  well,  therefore,  to  consider  the  composition  of 
the  various  substances  employed  as  food,  and  then  to  consider  how 
they  are  affected  by  cooking. 


ii  \p.  vii.]  NITROGENOUS    FOODS.  265 


A.— Poods  containing  principally  nitrogenous  bodies. 

I. — Flesh  of  Animals,  especially  of  the  ox  (beef,  veal),  slice]) 
(mutton,  lamb),  pig  (pork,  bacon,  ham). 

Of  these,  beef  is  richest  in  nitrogenous  matters,  containing 
about  20  per  cent.,  whereas  mutton  contains  about  18  per  cent., 
veal,  1 6*5,  and  pork,  10  ;  the  flesh  is  also  firmer,  more  satisfying, 
and  is  supposed  to  be  more  strengthening  than  mutton,  whereas 
the  latter  is  more  digestible.  The  flesh  of  young  animals,  such  as 
lamb  and  veal,  is  less  digestible  and  less  nutritious.  Pork  is 
comparatively  indigestible,  and  contains  a  large  amount  of  fat. 

Flesh  contains: — (1)  Nitrogenous  bodies:  myosin,  serum-albu- 
min, gelatin  (from  the  interstitial  fibrous  connective  tissue) ;  elastin 
(from  the  elastic  tissue),  as  well  as  haemoglobin.  (2)  Fatty  matters, 
including  lecithin  and  cholesterin.  (3)  Extractive  matters,  some  of 
which  are  agreeable  to  the  palate,  e.g.,  osmazome,  and  others  which 
are  weakly  stimulating,  e.g.,  kreatin.  Besides,  there  are  sarcolactic 
and  inositic  acids,  taurin,  xanthin,  and  others.  (4)  Salts,  chiefly  of 
potassium,  calcium,  and  magnesium.  (5)  Water,  the  amount  of 
which  varies  from  15  per  cent,  in  dried  bacon  to  39  in  pork, 
51  to  53  in  fat  beef  and  mutton,  to  72  per  cent,  in  lean  beef  and 
mutton.  (6)  A  certain  amount  of  carbo-hydrate  material  is  found 
in  the  flesh  of  some  animals,  in  the  form  of  inosite,  dextrin,  grape 
sugar,  and  (in  young  animals)  glycogen. 


Table  of  Per-centage  Composition  of  Beef,  Mutton,  Pork, 
and  veal. — (letheby.) 

"Water.        Albumen.  Fat.  Salts. 

Beef. — Lean   . 

Fat        .         . 
Mutton. — Lean 

„  Fat 

Veal         .... 
Pork.— Fat 


Together  with  the  flesh  of  the  above-mentioned  animals,  that  of 
the  deer,  hare,  rabbit,  and  birds,  constituting  venison,  game,  and 
poultry,  should  be  added  as  taking  part  in  the  supply  of  nitro- 


72 

I9-3 

3* 

5i 

51 

14-8 

29-8 

4"4 

72 

183 

4'9 

4-8 

53 

12*4 

31-1 

3-5 

.       63 

16-5 

158 

47 

39 

9-8 

48-9 

23 

78 

iS  i 

2-9 

I" 

77 

161 

5'5 

i*4 

75 

9'9 

13-8 

1 '3 

7574 

1172 

2*42 

273 

266  FOOD.  [chai\  vii. 

genous  substances,  and  also  fish — salmon,  eels,  &c.,  and  shell-fish, 
e.g.,  lobster,  crab,  mussels,  oysters,  shrimps,  scollop,  cockles,  &c. 

Table  of  Per-cextage  Composition  of  Poultry  and  Fish. — 

(Lethebt.) 

"Water.        Albumen.  Fats.  Salts. 

Poultry 74  21  3S  11 

(Singularly  devoid  of  fat,  and  so  generally  eaten  with  bacon  or 
pork.) 

White  Fish         .... 

Salmon 

Eels  (very  rich  in  fat)        .     . 
Oysters 

Even  now  the  list  of  fleshy  foods  is  not  complete,  as  nearly  all 
animals  have  been  occasionally  eaten,  and  we  may  presume  that 
the  average  composition  of  all  is  nearly  the  same. 

II.  Milk — Is  intended  as  the  entire  food  of  young  animals,  and 
as  such  contains,  when  pure,  all  the  elements  of  a  typical  diet. 
(1)  Albuminous  substances  in  the  form  of  casein  and,  in  small 
amount,  of  serum-albumin.  (2)  Fats  in  the  cream.  (3)  Carbo- 
hydrates in  the  form  of  lactose  or  milk  sugar.  (4)  Salts,  chiefly 
calcium  phosphate;  and  (5)  Water.  From  it  we  obtain  (a)  cheese, 
which  is  the  casein  precipitated  with  more  or  less  fat  according 
as  the  cheese  is  made  of  skim  milk,  (skim  cheese),  of  fresh  milk 
with  its  cream  (Cheddar  and  Cheshire),  or  of  fresh  milk  plus 
cream  (Stilton  and  double  Gloucester).  The  precipitated  casein 
is  allowed  to  ripen,  by  which  process  some  of  the  albnmen  is 
split  up  with  formation  of  fat.  (/3)  Cream,  which  consists  of  the 
fatty  globules  incased  in  casein,  and  which  being  of  low  specific 
oTavity  float  to  the  surface.  (y)  Butter,  or  the  fatty  matter 
deprived  of  its  casein  envelope  by  the  process  of  churning. 
(S)  Butter-mill:,  or  the  fluid  obtained  from  cream  after  butter  has 
been  formed ;  very  rich  therefore  in  nitrogen,  (e)  Whey,  or  the 
fluid  which  remains  after  the  precipitation  of  casein  ;  this  contains 
sugar,  salt,  and  a  small  quantity  of  albumen. 


chap,  vii.]        CARBOHYDRATE    AND    FATTY    FOODS.  267 

Table  of  Composition'  of  Milk,  Butteb-milk,  Cream,  and 
Cheese. — (I.ltiii.uv  and  1'avi 

Nitrogenous  matters.    I"  Lactose.        Salts.    Wa* 


Milk  {Cow)    . 

41 

39 

5'2 

•s 

86 

Buttermilk 

41 

7 

6-4 

•8 

88 

Cream    . 

27 

267 

2*8 

1-8 

66 

-  . — Skim    . 

.      44-8 

63 

— 

4"9 

44 

Cheddar    . 

.      28-4 

311 

Non-nitrogenous 
matter  and  loss. 

4*5 

36 

„      Neufchatel  (Fresh)  S* 

4071 

36-58 

•5i 

36 

Salts. 

"Water 

1-6 

7S 

i*3 

52 

III.  Eggs. — The  yelk  and  albumen  of  eggs  are  in  the  same 
relation  as  food  for  the  embryoes  of  oviparous  animals  that  milk 
is  to  the  young  of  mammalia,  and  afford  another  example  of  the 
natural  admixture  of  the  various  alimentary  principles. 

Table  of  the  Per-centage  Composition  of  Fowls*  Egg>. 

Nitrogenous  substances.    Fats. 
White  .        .         .     .       20*4  — 

Yelk  16-  307 

IV.  Leguminous  fruits  are  used  by  vegetarians,  as  the  chief  source 
of  the  nitrogen  of  the  food.  Those  chiefly  used  are  peas,  leans, 
lentil*,  atc,  they  contain  a  nitrogenous  substance  called  legumin, 
allied  to  albumen.  They  contain  about  2  5  '30  per  cent,  of  this 
nitrogenous  body,  and  twice  as  much  nitrogen  as  wheat. 

B.  Substances  supplying  principally  carbohydrate 

bodies. 

a.  Bread,  made  from  the  ground  grain  obtained  from  various 
so-called  cereals,  viz.,  wheat,  rye,  maize,  barley,  rice,  oats,  Arc,  is 
the  direct  form  in  which  the  carbohydrate  is  supplied  in  an 
ordinary  diet.  Flour,  however,  besides  the  starch,  contains  gluten, 
a  nitrogenous  body,  and  a  small  amount  of  fat. 

Table  of  Per-centage  Composition  of  Bread  and  Flour. 


Nitrogenous 

Carbo- 

matters. 

hydrates. 

Fats. 

Salts. 

"Wat< 

8l 

5i' 

r6 

2"3 

37 

108 

7o-S5 

n* 

17 

15 

Bread 

Hour 

Various  articles  of  course  are  made  from  flour,  e.g.,  macaroni, 
biscuits,  <fcc.,  besides  bread. 


268  FOOD.  [chap.  vii. 

j8.   Vegetables,  especially  potatoes. 

y.  Friiits  contain  sugar,  and  organic  acids,  tartaric,  malic,  citric, 
and  others. 

C.  Substances  supplying  principally  fatty  bodies. 

The  chief  are  butter,  lard  (pig's  fat),  suet  (beef  and  mutton  fat). 

D.  Substances  supplying  the  salts  of  the  food. 

Nearly  all  the  foregoing  substances  in  A,  B,  and  C,  contain  a 
greater  or  less  amount  of  the  salts  required  in  food;  but  green 
vegetables  and  fruit  supply  certain  salts,  without  which  the 
normal  health  of  the  body  is  not  maintained. 

E.  Liquid  foods. 

Water  is  consumed  alone,  or  together  with  certain  other  sub- 
stances used  to  flavour  it,  e.g.,  tea,  coffee,  &c.  Tea  in  moderation 
is  a  stimulant,  and  contains  an  aromatic  oil  to  which  it  owes  its 
peculiar  aroma,  an  astringent  of  the  nature  of  tannin,  and  an  alka- 
loid, theme.  The  composition  of  coffee  is  very  nearly  similar  to 
that  of  tea.  Cocoa,  in  addition  to  similar  substances  contained 
in  tea  and  coffee,  contains  fat,  albuminous  matter,  and  starch,  and 
must  be  looked  upon  more  as  a  food. 

Beer,  in  various  forms,  is  an  infusion  of  malt  (barley  which  has 
sprouted,  and  in  which  the  starch  is  converted  in  great  part  into 
sugar),  boiled  with  hops  and  allowed  to  ferment.  Beer  contains 
from  i*2  to  8*8  per  cent,  of  alcohol. 

Cider  and  Perry,  the  fermented  juice  of  the  apple  and  pear. 

Wine,  the  fermented  juice  of  the  grape,  contains  from  6  or  7 
(Rhine  wines,  and  white  and  red  Bordeaux)  to  24 — 25  (ports  and 
sherries)  per  cent,  of  alcohol. 

Spirits,  obtained  from  the  distillation  of  fermented  liquors.  They 
contain  upwards  of  40 — 70  per  cent,  of  absolute  alcohol. 

Effects  of  cooking  upon  Food. — In  general  terms  this  may 
be  said  to  make  food  more  easily  digestible,  and  this  includes  two 
other  alterations,  food  is  made  more  agreeable  to  the  palate  and  also 
more  pleasing  to  the  eye.  Cooking  consists  in  exposing  the  food 
to  various  degrees  of  heat,  either  to  the  direct  heat  of  the  fire,  as 
in  roasting,  or  to  the  indirect  heat  of  the  fire,  as  in  broiling, 
baking,  or  frying,  or  to  hot  water,  as  in  boiling  or  stewing.     The 


(hap.  vii.]         EFFECTS    OF    [^SUFFICIENT    DIET.  269 

effect  of  heat  upon  -  to  coagulate  the  albumen  and  colouring 

matter,  to  solidity  fibrin,  and  to  gelatinize  tendons  and  fibrous  con- 
nective tissue.  Previous  beating  or  bruising  (as  with  steaks  and 
chops,  or  keeping  (as  in  the  case  of  game),  renders  the  meat  mora 

tender.     Prolonged  exposure  to  heat  also  develops  on  the  surface 
certain  empyreumatic  bodies,  which  are  agreeable  both  to  the  tae 
and  smell.    By  placing  meat  into  hot  water,  the  external  _  of 

albumen  is  coagulated,  and  very  little,  if  any,  of  the  constituei 
of  the  meat  are  lost  afterwards  if  boiling  be  prolonged,  but  if  the 
constituents  of  the  meat  are  to  be  extracted,  it  should  be  expo- 
to  prolonged  Bimmering  at  a  much  lower  temperature,  and  the 
"broth"  will  then  contain  the  gelatin  and  extractive  matters  of 
the  meat,  as  well  as  a  certain  amount  of  albumen.  The  addition 
of  salt  will  help  to  extract  the  myosin. 

The  effect  of  boiling  upon  an  egg  coagulates  the  albumen,  and 
helps  in  rendering  the  article  of  food  more  suitable  for  adult 
dietary.  Upon  milk,  the  effect  of  heat  is  to  produce  a  scum  com- 
posed of  serum-albumin  and  a  little  casein  (the  greater  part  of  the 

sein  being  imcoagulated)  with  some  fat.  Upon  vegetables,  the 
cooking  produces  the  necessary  effect  of  rendering  them  softer,  so 
that  they  can  be  more  readily  broken  up  in  the  mouth ;  it  also 
causes  the  starch  to  swell  up  and  burst,  and  so  aids  the  digestive 
fluids  to  penetrate  into  their  substance.  The  albuminous  matters 
are  coagulated,  and  the  gummy,  saccharine  and  saline  matters  are 
removed.  The  conversion  of  flour  into  bread  is  effected  by  mixing- 
it  with  water,  a  little  salt  and  a  certain  amount  of  yeast,  which 
consists  of  the  cells  of  an  organised  ferment  (Torula  cerevisice). 
By  the  growth  of  this  plant,  which,  lives  upon  the  sugar  produced 
from  the  starch  of  the  flour,  carbonic  acid  gas  and  a  small  amount 
of  alcohol  are  formed.  It  is  by  means  of  the  former  that  the 
dough  rises.  Another  method  consists  in  mixing  the  flour  with 
water  containing  a  large  quantity  of  the  gas  in  solution. 

By  the  action  of  heat  during  baking  the  dough  continues  to 
expand,  and  the  gluten  being  coagulated,  the  bread  sets  as  a 
permanently  vesiculated  mass. 

I.— Effects  of  an  insufficient  diet. 
Hunger  and  Thirst. — The  sensation  of  hunger  is  manifested 
in  consequence  of  deficiency  of  food  in  the  system.     The  mind 


270  FOOD.  [chap.  vn. 

refers  the  sensation  to  the  stomach ;  yet  since  the  sensation  is 
relieved  by  the  introduction  of  food  either  into  the  stomach  itself, 
or  into  the  blood  through  other  channels  than  the  stomach,  it 
would  appear  not  to  depend  on  the  state  of  the  stomach  alone. 
This  view  is  confirmed  by  the  fact,  that  the  division  of  both  pneu- 
mogastric  nerves,  which  are  the  principal  channels  by  which  the 
brain  is  cognisant  of  the  condition  of  the  stomach,  does  not  appear 
to  allay  the  sensations  of  hunger.  But  that  the  stomach  has 
some  share  in  this  sensation  is  proved  b}r  the  relief  afforded, 
though  only  temporarily,  by  the  introduction  of  even  non-alimen- 
tary substances  into  this  organ.  It  may,  therefore,  be  said  that 
the  sensation  of  hunger  is  caused  both  by  a  want  in  the  system 
generally,  and  also  by  the  condition  of  the  stomach  itself,  by 
which  condition,  of  course,  its  own  nerves  are  more  directly 
affected. 

The  sensation  of  thirst,  indicating  the  want  of  fluid,  is  referred 
to  the  fauces,  although,  as  in  hunger,  this  is,  in  great  part,  only  the 
local  declaration  of  a  general  condition.  For  thirst  is  relieved  for 
only  a  very  short  time  by  moistening  the  dry  fauces  ;  but  may  be 
relieved  completely  by  the  introduction  of  liquids  into  the  blood, 
either  through  the  stomach,  or  by  injections  into  the  blood-vessels, 
or  by  absorption  from  the  surface  of  the  skin  or  the  intestines. 
The  sensation  of  thirst  is  perceived  most  naturally  whenever  there 
is  a  disproportionately  small  quantity  of  water  in  the  blood  :  as 
well,  therefore,  when  water  has  been  abstracted  from  the  blood, 
as  when  saline  or  any  solid  matters  have  been  abundantly  added 
to  it.  And  the  cases  of  hunger  and  thirst  are  not  the  only  ones 
in  which  the  mind  derives,  from  certain  organs,  a  peculiar  pre- 
dominant sensation  of  some  condition  affecting  the  whole  body. 
Thus,  the  sensation  of  the  "  necessity  of  breathing,"  is  referred 
especially  to  the  air-passages ;  but,  as  Volkmann's  experiments  show, 
it  depends  on  the  condition  of  the  blood  which  circulates  every- 
where, and  is  felt  even  after  the  lungs  of  animals  are  removed ;  for 
they  continue,  even  then,  to  gasp  and  manifest  the  sensation  of 
want  of  breath. 

Starvation. — The  effects  of  total  deprivation  of  food  have 
been  made  the  subject  of  experiments  on  the  lower  animals,  and 
have  been  but  too  frequently  illustrated  in  man.  (i.)  One  of  the 
most  notable  effects  of  starvation,  as  might  be  expected,  is  loss  of 


CHAP,  vii.] 


STARVATION. 


271 


weight  ;  the  loss  being  greatest  ;it  first,  as  a  rule,  but  afterwards 
not  varying  very  much,  day  by  day,  until  death  ensues.  Ch< 
found  that  the  ultimate  proportional  loss  was,  in  differenl  animals 
experimented  on,  almost  exactly  the  same  \  deatb  occurring  when 
the  body  had  lost  two-fifths  (forty  per  cent.)  of  its  original  weight. 
Different  parts  of  the  body  lose  weight  in  very  different  proportions. 
The  following  results  are  taken,  in  round  numbers,  from  the  table 
given  by  M.  Chossat : — 


Fat          .... 
Spleen   .... 

Intestines 

Muscles  of  locomotion 

Stomach 

Pharynx,  (Esophagus 

Skin       .... 

Eespiratory  apparatus  . 

Eyes       .... 
Nervous  svstem 

loses  . 

93  per  cent. 

75 

?> 

7i 

55 

64 

55 

52 

55 

44 

>l 

42 

55 

42 

55 

39 

55 

34 

55 

33 

55 

3i 

55 

22 

55 

16 

55 

10 

55 

2 

,.  (ne 

(2.)  The  effect  of  starvation  on  the  temperature  of  the  various 
animals  experimented  on  by  Chossat  was  very  marked.  For 
some  time  the  variation  in  the  daily  temperature  was  more  marked 
than  its  absolute  and  continuous  diminution,  the  daily  fluctua- 
tion amounting  to  50  or  6°  F.  (30  C),  instead  of  i°  or  20  F. 
(■50  to  i°  C),  as  in  health.  But  a  short  time  before  death, 
the  temperature  fell  very  rapidly,  and  death  ensued  when  the 
loss  had  amounted  to  about  30°  F.  (16-5°  C.)  It  has  been 
often  said,  and  with  truth,  although  the  statement  requires  some 
qualification,  that  death  by  starvation  is  really  death  by  cold ;  for 
not  only  has  it  been  found  that  differences  of  time  with  regard  to 
the  period  of  the  fatal  result  are  attended  by  the  same  ultimate 
loss  of  heat,  but  the  effect  of  the  application  of  external  warmth  to 
animals  cold  and  dying  from  starvation,  is  more  effectual  in  reviving 
them  than  the  administration  of  food.  In  other  words,  an  animal 
exhausted  by  deprivation  of  nourishment  is  unable  so  to  digest 
food  as  to  use  it  as  fuel,  and  therefore  is  dependent  for  heat  on 


272  FOOD.  [chap.  vii. 

its  supply  from  without.  Similar  facts  are  often  observed  in  the 
treatment  of  exhaustive  diseases  in  man. 

(3.)  The  symptoms  produced  by  starvation  in  the  human  sub- 
ject are  hunger,  accompanied,  or  it  may  be  replaced  by  pain, 
referred  to  the  region  of  the  stomach  ;  insatiable  thirst ;  sleep- 
lessness ;  general  weakness  and  emaciation.  The  exhalations  both 
from  the  lungs  and  skin  are  fetid,  indicating  the  tendency  to 
decomposition  which  belongs  to  badly-nourished  tissues ;  and 
death  occurs,  sometimes  after  the  additional  exhaustion  caused 
by  diarrhoea,  often  with  symptoms  of  nervous  disorder,  delirium 
or  convulsions. 

(4.)  In  the  human  subject  death  commonly  occurs  within  six  to 
ten  days  after  total  deprivation  of  food.  But  this  period  may  be 
considerably  prolonged  by  taking  a  very  small  quantity  of  food,  or 
even  water  only.  The  cases  so  frequently  related  of  survival  after 
many  days,  or  even  some  weeks,  of  abstinence,  have  been  due 
either  to  the  last-mentioned  circumstances,  or  to  others  no  less 
effectual,  which  prevented  the  loss  of  heat  and  moisture.  Cases 
in  which  life  has  continued  after  total  abstinence  from  food  and 
drink  for  many  weeks,  or  months,  exist  only  in  the  imagination  of 
the  vulgar. 

(5.)  The  appearances  presented  after  death  from  starvation  are 
those  of  general  wasting  and  bloodlessness,  the  latter  condition 
beino*  least  noticeable  in  the  brain.  The  stomach  and  intestines 
are  empty  and  contracted,  and  the  walls  of  the  latter  appear 
remarkably  thinned  and  almost  transparent.  The  various  secre- 
tions are  scanty  or  absent,  with  the  exception  of  the  bile,  which, 
somewhat  concentrated,  usually  fills  the  gall-bladder.  All  parts  of 
the  body  readily  decompose. 

II.— Effects  of  Improper  Diet. 

Experiments  on  Feeding. — Experiments  illustrating  the  ill 
effects  produced  by  feeding  animals  upon  one  or  two  alimentary 
substances  only  have  been  often  performed. 

Dogs  were  fed  exclusively  on  sugar  and  distilled  water.  During 
the  first  seven  or  eight  days  they  were  brisk  and  active,  and  took 
their  food  and  drink  as  usual ;  but  in  the  course  of  the  second 
week,  they  began  to  get  thin,  although  their  appetite  continued 


CHAP.  VII.]  STARVATION.  273 

good,  and  they  took  daily  between  six  and  eight  ounces  of  sugar. 
The  emaciation  increased  during  the  third  week,  and  they  became 
feeble,  and  lost  their  activity  and  appetite.  At  the  same  time  an 
ulcer  formed  on  each  cornea,  followed"  by  an  escape  of  the  humours 
of  the  e}re  :  this  took  place  in  repeated  experiments.  The  animals 
still  continued  to  eat  three  or  four  ounces  of  sugar  daily ;  but 
became  at  length  so  feeble  as  to  be  incapable  of  motion,  and  died 
on  a  day  varying  from  the  thirty-first  to  the  thirty-fourth.  On 
dissection,  their  bodies  presented  all  the  appearances  produced  by 
death  from  starvation ;  indeed,  dogs  will  live  almost  the  same 
length  of  time  without  any  food  at  all. 

When  dogs  were  fed  exclusively  on  gum,  results  almost  similar 
to  the  above  ensued.  When  they  were  kept  on  olive-oil  and  water, 
all  the  phenomena  produced  were  the  same,  except  that  no  ulcera- 
tion of  the  cornea  took  place  ;  the  effects  were  also  the  same  with 
butter.  The  experiments  of  Chossat  and  Letellier  prove  the  same  \ 
and  in  men,  the  same  is  shown  by  the  various  diseases  to  which 
those  who  consume  but  little  nitrogenous  food  are  liable,  and 
especially  by  the  affection  of  the  cornea  which  is  observed  in 
Hindus  feeding  almost  exclusively  on  rice.  But  it  is  not  only  the 
non-nitrogenous  substances,  which,  taken  alone,  are  insufficient  for 
the  maintenance  of  health.  The  experiments  of  the  Academies  of 
France  and  Amsterdam  were  equally  conclusive  that  gelatin  alone 
soon  ceases  to  be  nutritive. 

Savory's  observations  on  food  confirm  and  extend  the  results 
obtained  by  Magendie,  Chossat,  and  others.  They  show  that 
animals  fed  exclusively  on  non-nitrogenous  diet  speedily  emaciate 
and  die,  as  if  from  starvation  •  that  life  is  much  more  prolonged  in 
those  fed  with  nitrogenous  than  by  those  with  non-nitrogenous 
food  ;  and  that  animal  heat  is  maintained  as  well  by  the  former  as 
by  the  latter — a  fact  which  proves,  if  proof  were  wanting — that 
nitrogenous  elements  of  food,  as  well  as  non-nitrogenous,  may  be 
regarded  as  calorifacient. 


III.— Effect  of  Too  Much  Food. 

Sometimes  the  excess  of  food  is  so  great  that  it  passes  through 
the  alimentary  canal,  and  is  at  once  got  rid  of  by  increased  peristaltic 

x 


274  FOOD.  [chap.  vii. 

action  of  the  intestines.  In  other  cases,  the  nnabsorbed  portions 
undergo  putrefactive  changes  in  the  intestines,  which  are  ac- 
companied by  the  production  of  gases,  such  as  carbonic  acid, 
carbnretted  and  sulphuretted  hydrogen  ;  a  distended  condition  of 
the  bowels,  accompanied  by  s}miptorns  of  indigestion,  is  the  result. 
An  excess  of  the  substances  required  as  food  may  however  undergo 
absorption.  It  is  a  well-known  fact  that  numbers  of  people 
habitually  eat  too  much ;  especially  of  nitrogenous  food.  Dogs 
can  digest  an  immense  amount  of  meat  if  fed  often,  and  the 
amount  of  meat  taken  by  some  men  would  supply  not  only 
the  nitrogen,  bnt  the  carbon  which  is  requisite  for  an  ordinary 
natural  diet.  A  method  of  getting  rid  of  an  excess  of  nitrogen 
is  provided  by  the  digestive  processes  in  the  duodenum,  to  be 
presently  described,  whereby  the  excess  of  the  albuminous  food 
is  capable  of  being  changed  before  absorption  into  nitrogenous 
crystalline  matters,  easily  converted  by  the  liver  into  urea,  and  so 
easily  excreted  by  the  kidneys,  affording  one  variety  of  what  is 
called  luxus  consumption  ;  but  after  a  time  the  organs,  especially 
the  liver,  will  yield  to  the  strain  of  the  over-work,  and  will  not 
reduce  the  excess  of  nitrogenous  material  into  urea,  but  into  other 
less  oxidised  products,  such  as  uric  acid ;  and  general  plethora 
and  gout  may  be  the  result.  This  state  of  things,  however,  is 
delayed  for  a  long  time,  if  not  altogether  obviated,  when  large 
meat-eaters  take  a  considerable  amount  of  exercise. 

Excess  of  carbohydrate  food  produces  an  accumulation  of  fat, 
which  may  not  only  be  an  inconvenience  by  causing  obesity, 
but  may  interfere  with  the  proper  nutrition  of  muscles,  causing 
a  feebleness  of  the  action  of  the  heart,  and  other  troubles. 
The  accumulation  of  fat  is  due  to  the  excess  of  carbohydrate  being 
stored  up  by  the  protoplasm  in  the  form  of  fat.  Starches  when 
taken  in  great  excess  are  almost  certain  to  give  rise  in  addition 
to  dyspepsia,  with  acidity  and  flatulence.  There  is  a  limit  to  the 
absorption  of  starch  and  of  fat,  as,  if  taken  beyond  a  certain 
amount,  they  appear  unchanged  in  the  faeces. 

Requisites  of  a  Normal  Diet. — It  will  have  been  understood 
that  it  is  necessary  that  a  normal  diet  should  be  made  up  of  various 
articles,  that  they  should  be  well  cooked,  and  should  contain  about 
the  same  amount  of  the  carbon  and  nitrogen  that  are  got  rid  of  by 
the  excreta.      Without  doubt  these  desiderata  may  be  satisfied  in 


CHAP,  vii.]  NOEMAL    DIET.  27t 

numerous  ways,  and  it  would  be  simply  absurd  to  believe  that  the 
diet  of  every  adult  should  be  exactly  similar.  The  age,  sex,  strength, 
and  circumstances  of  cadi  individual  should  ultimately  determine 

his  diet.  A  dinner  of  bread  and  hard  cheese  with  an  onion 
contain  all  the  requisites  for  a  meal;  but  such  diet  would  he 
suitable  only  for  those  possessing  strong  digestive  powers.  It  is  a 
well-known  fact  that  the  diet  of  the  continental  nations  differs 
from  that  of  our  own  country,  and  that  of  cold  from  that  of  hot 
climates;  but  the  same  principle  underlies  them  all,  viz.,  replace- 
ment of  the  loss  of  the  excreta  in  the  most  convenient  and 
economical  way  possible.  Without  going  into  detail  in  the 
matter,  it  may  be  said  that  anyone  in  active  work  requires  more 
nitrogenous  matter  than  one  at  rest,  and  that  children  and 
women  require  less  than  adult  men. 

The  quantity  of  food  for  a  healthy  adult  man  of  average  height 
and  weight  may  be  stated  in  the  following  table  : — 

Table  of  Water  and  Food  required  for  a  Healthy  Adult. 

(Parkes.) 

In  laborious 

occupation.  At  rest. 

Nitrogenous  substances,  e.g.,  flesh    .            6  to  7  oz.  av.  2-5  oz. 

Fats 3'5  ^  4-5  oz.  1  oz. 

Carbo-hydrates 16  to  18  oz.  12  oz. 

Salts i-2  to  i*5  oz.  '5  oz. 


267  to  31  oz.  16  oz. 

The  above  is  the  dry  food;  but  as  this  is  nearly  always 
combined  with  50  to  60  per  cent,  of  water,  these  numbers 
should  be  doubled,  and  they  would  then  be  52  to  60  oz.,  and 
32  oz.  of  so  called  solid  food,  and  to  this  should  be  added  50  to 
80  oz.  of  fluid. 


Full  diet  scale  for  an  adult  male  in  hospital  (St.  Bartholomew's 

Hospital). 

Breakfast.— 1  pint  of  tea  (with  milk  and  sugar),  bread  and  butter. 
Dinner.— £lb.  of  cooked  meat,  £lb.  potatoes,  bread  and  beer. 
Tea. —  1  pint  of  tea,  bread  and  butter. 
Supjper. — Bread  and  butter,  beer. 

t  2 


2j6  DIGESTION.  [chap.  yiii. 

Daily  allowance  to  each  patient. — 2  pints  cf  tea,  with  milk  and  sugar  ; 
14  oz.  bread ;  i  lb.  of  cooked  meat  :  §  lb.  potatoes  :  2  pints  of  beer,  1  oz. 
butter.     31  oz.  solid,  and  4  pints  (80  oz.),  liquid. 


CHAPTER   VIII. 

DIGESTION. 


The  object  of  digestion  is  to  prepare  the  food  to  supply  the 
waste  of  the  tissues,  which  we  have  seen  is  its  proper  function  in 
the  economy.  Few  of  the  articles  of  diet  are  taken  in  the  exact 
condition  in  which  it  is  possible  for  thern  to  be  absorbed  into  the 
system  by  the  blood  vessels  and  lymphatics,  without  which  absorp- 
tion they  would  be  useless  for  the  purposes  they  have  to  fulfil ; 
almost  the  whole  of  the  food  undergoes  various  changes  before  it 
is  fit  for  absorption.  Having  been  received  into  the  mouth,  it  is 
subjected  to  the  action  of  the  teeth  and  tongue,  and  is  mixed 
with  the  first  of  the  digestive  juices — the  saliva.  It  is  then 
swallowed,  and,  passing  through  the  pharynx  and  oesophagus  into 
the  stomach,  is  subjected  to  the  action  of  the  gastric  juice.  Thence 
it  passes  into  the  intestines,  where  it  meets  with  the  bile,  the 
pancreatic  juice  and  the  intestinal  juices,  all  of  which  exercise 
an  influence  upon  that  portion  of  the  food  not  absorbed  from  the 
stomach.  By  this  time  most  of  the  food  is  capable  of  absorption, 
and  the  residue  of  undigested  matter  leaves  the  body  in  the  fomi 
of  faeces  by  the  anus. 

The  course  of  the  food  through  the  alimentary  canal  of  man 
will  be  readily  seen  from  the  accompanying  diagram  (fig.  165). 

The  Mouth  is  the  cavity  contained  between  the  jaws  and  inclosed 
by  the  cheeks  laterally,  and  by  the  lips  in  front ;  behind  it  opens 
into  the  pharynx  by  the  fauces,  and  is  separated  from  the  nasal 
cavity  by  the  hard  palate  in  front,  and  the  soft  palate  behind,  which 
form  its  roof.  The  tongue  forms  the  lower  part  or  floor.  In  the 
jaws  are  contained  the  teeth;  and  when  the  mouth  is  shut  these 
form  its  anterior  and  lateral  boundaries.  The  whole  of  the  mouth 
is  lined  with  mucous  membrane,  covered  by  stratified  squamous 
epithelium,  which  is  continuous  in  front  along  the  lips  with  the 


OHAP.  VIII.  1 


COURSE    TAKEN    BY    THE    FOOD. 


277 


epithelium  of  the  skin,  and  posteriorly  with  that  of  the  pharynx. 
The  mucous  membrane  is  provided  with  numerous  glands  (small 
tubular),  called  mucous  glands,  and  into  it  open  the  ducts  of  the 


Got  1 1 
Blotddei ■■', 


Ltver 
tufiteduJi 


. —  Pharynx 


•J?      •    *\ 


"Ion     Y>5V 


<^    "~  Petri  erects 


-KjC 'Jj2=^ij\vA  St?,notd 


Intestine      II   j>  J! 


Fig.  165.— Diagram  of  the  Alimentary  Canal.    The  small  intestine  of  man  is  from  about 
3  to  4  times  as  long  as  the  large  intestine. 

salivary  glands,  three  chief  glands  on  each  side.  The  tongue  is 
not  only  a  prehensile  organ,  but  is  also  the  chief  seat  of  the  sense 
of  taste. 

We  shall  now  consider,  in  detail,  the  process  of  digestion,  as  it 
takes  place  in  each  stage  of  this  journey  of  the  food  through  the 
alimentary  canal. 


2yS  DIGESTION.  [chap.  viii. 

Mastication. — The  act  of  chewing  or  mastication  is  performed 
by  the  biting  and  grinding  movement  of  the  lower  range  of  teeth 
against  the  upper.  The  simultaneous  movements  of  the  tongue 
and  cheeks  assist  partly  by  crushing  the  softer  portions  of  the 
food  against  the  hard  palate,  gums,  &c,  and  thus  supplementing 
the  action  of  the  teeth,  and  partly  by  returning  the  morsels  of 
food  to  the  action  of  the  teeth,  again  and  again,  as  they  are 
squeezed  out  from  between  them,  until  they  have  been  sufficiently 
chewed. 

The  simple  up  and  down,  or  biting  movements  of  the  lower 
jaw,  are  performed  by  the  temporal,  masseter,  and  internal  pterygoid 
muscles,  the  action  of  which  in  closing  the  jaws  alternates  with 
that  of  the  digastric  and  other  muscles  passing  from  the  os  hyoides 
to  the  lower  jaw,  which  open  them.  The  grinding  or  side  to  side 
movements  of  the  lower  jaw  are  performed  mainly  by  the  external 
pterygoid  muscles,  the  muscle  of  one  side  acting  alternately  with 
the  other.  When  both  external  pterygoids  act  together,  the  lower 
jaw  is  pulled  directly  forwards,  so  that  the  lower  incisor  teeth  are 
brought  in  front  of  the  level  of  the  upper. 

Temporo-maxillary  Fibro-cartilage. — The  function  of  the 
inter-articular  fibro-cartilage  of  the  temporo-maxillary  joint  in 
mastication  may  be  here  mentioned,  (i)  As  an  elastic  pad,  it 
serves  well  to  distribute  the  pressure  caused  by  the  exceedingly 
powerful  action  of  the  masticatory  muscles.  (2)  It  also  serves  as  a 
joint-surface  or  socket  for  the  condyle  of  the  lower  jaw,  when  the 
latter  has  been  partially  drawn  forward  out  of  the  glenoid  cavity 
of  the  temporal  bone  by  the  external  pterygoid  muscle,  some  of 
the  fibres  of  the  latter  being  attached  to  its  front  surface,  and 
consequently  drawing  it  forward  with  the  condyle  which  moves 
on  it. 

Nerve-mechanism  of  mastication. — As  in  the  case  of  so 
many  other  actions,  that  of  mastication  is  partly  voluntary  and 
partly  reflex  and  involuntary.  The  consideration  of  such  sensori- 
motor actions  will  come  hereafter  (see  Chapter  on  the  Nervous 
System).  It  will  suffice  here  to  state  that  the  nerves  chiefly  con- 
cerned are  the  sensory  branches  of  the  fifth  and  the  glossopharyn- 
geal, and  the  motor  branches  of  the  fifth  and  the  ninth  (hypoglos- 
sal) cerebral  nerves.  The  nerve-centre  through  which  the  reflex 
action  occurs,  and  by  which  the  movements  of  the  various  muscles 


P.  viii.]  SALIVARY    CLAN  279 

arc  harmonised,  is  situate  in  the  medulla  oblongata,  In  bo  far  as 
mastication  is  voluntary  or  mentally  perceived,  it  becomes  so 
under  the  influence,  in  addition  to  the  medulla  oblongata,  of  the 
cerebral  hemisphen 

Insalivation. — The  act  of  mastication  is  much  assisted  by  the 
saliva  which  is  secrete!  by  the  salivary  -lands  in  largely  incn 
amount   during   the    pn      38,    and    the    intimate   incorporation  of 
which  with  the  food,  as  it  is  being  chewed,  is  termed  insalivation. 


The  Salivary  Glands. 

The  salivary  glands  are  the  parotid,  the  subjmattllaryi  and  the 
tub-lingual,  and  numerous  smaller  bodies  of  similar  structure,  and 
with  separate  ducts,  which  are  scattered  thickly  beneath  the 
mucous  membrane  of  the  lips,  cheeks,  soft  palate,  and  root  of  the 
tongue. 

Structure. — The  salivary  glands  are  usually  described  as  com- 
pound  tubular   glands.     They   are    made    up   of  lobules.     Each 


'/>L 


1M* 


Mm 


Fig.  166.— Section  of  submaxillary  gland  of  don.    Showing  gland-cells,  b,  and  a  duct,  a,  in 

section.    (KGlliker.) 

lobule  consists  of  the  branchings  of  a  subdivision  of  the  main  duct 
of  the  gland,  which  are  generally  more  or  less  convoluted  towards 
their  extremities,   and  sometimes,   according   to  son.  -  rvera, 

sacculated  or  pouched.  The  convoluted  or  pouched  portions 
form  the  alveoli,  or  proper  secreting  parts  of  the  gland.  The 
alveoli  are  composed  of  a  basement  membrane  of  flattened  cells 


280 


DIGESTION. 


[chap.  VIII. 


Fig.  167. — From  a  section  through  a  true 
salivary  gland,  a,  the  gland  alveoli, 
lined  with  albuminous  "  salivary  cells  ;" 
b,  intralobular  duct  cut  transversely. 
(Klein  and  Noble  Smith.) 


joined  together  by  processes  to  produce  a  fenestrated  membrane, 
the  spaces  of  which  are  occupied  by  a  homogeneous  ground-sub- 
stance. Within,  upon  this  mem- 
brane, which  forms  the  tube,  the 
nucleated  salivary  secreting  cells, 
of  cubical  or  columnar  form, 
are  arranged  parallel  to  one  an- 
other surrounding  a  middle 
central  canal.  The  granular 
appearance  which  is  frequently 
seen  in  the  salivary  cells  is  due 
to  the  very  dense  network  of 
fibrils  which  they  contain.  When 
isolated,  the  cells  not  unfrequently 
are  found  to  be  branched.  Con- 
necting the  alveoli  into  lobules 
is  a  considerable  amount  of 
fibrous  connective  tissue,  which 
contains  both  flattened  and  granular  protoplasmic  cells,  lymph 
corpuscles,  and  in  some  cases  fat  cells.  The  lobules  are  con- 
nected to  form  larger  lobules  (lobes),  in  a  similar  manner.  The 
alveoli  pass  into  the  intralobular  ducts  by  a  narrowed  portion 
(intercalary),  lined  with  flattened  epithelium  with  elongated 
nuclei.  The  intercalary  ducts  pass  into  the  intralobular  ducts 
by  a  narrowed  neck,  lined  with  cubical  cells  with  small  nuclei. 
The  intralobular  duct  is  larger  in  size,  and  is  lined  with  large 
columnar  nucleated  cells,  the  parts  of  which,  towards  the  lumen 
of  the  tube  presents  a  fine  longitudinal  striation,  due  to  the 
arrangement  of  the  cell  network.  It  is  most  marked  in  the 
submaxillary  gland.  The  intralobular  ducts  pass  into  the  larger 
ducts,  and  these  into  the  main  duct  of  the  gland.  As  these 
ducts  become  larger  they  acquire  an  outside  coating  of  connective 
tissue,  and  later  on  some  unstriped  muscular  fibres.  The  lining 
of  the  larger  ducts  consists  of  one  or  more  layers  of  columnar 
epithelium,  containing  an  intracellular  network  of  fibres  arranged 
longitudinally. 

Varieties. — Certain  differences  in  the  structure  of  salivary 
glands  may  be  observed  according  as  the  glands  secrete  pure 
saliva,  or  saliva  mixed  with  mucus,  or  pure  mucus,  and  therefore 


OHAP.  VIII.] 


SALIVARY    GLANDS. 


28l 


the  glands  have  been  classified  as  :  (1)  True  salivary  glands  (called 
most  unfortunately  by  some  serous  glands),  e.g.,  the  parotid  of  man 

and  other  animals,  and  the  submaxillary  of  the  rabbit  and  guinea- 
pig  (fig.  167).  In  this  kind  the  alveolar  lumen  is  small,  and  the 
cells  lining  the  tubule  are  short,  granular  columnar  cells,  with  nuclei 
presenting  the  intranuclear  network.  During  rest  the  cells  become 
larger,  highly  granular,  with  obscured  nuclei,  and  the  lumen  becomes 
smaller.  During  activity,  and  after  stimulation  of  the  sympathetic, 
the  cells  become  smaller  and  their  contents  more  opaque ;  the 
granules  first  of  all  disappearing  from  the  outer  part  of  the  cells, 
and  then  being  found  only  at  the  extreme  inner  part  and  contigu- 
ous border  of  the  cell.  The  nuclei  reappear,  as  does  also  the  lumen. 
(2)  In  the  true  mucus-secret- 
ing glands,  as  the  sublingual 
of  man  and  other  animals, 
and  in  the  submaxillary  of 
the  dog,  the  tubes  are 
larger,  contain  a  larger 
lumen  and  also  have  larger 
cells  lining  them.  The  cells 
are  of  two  kinds,  (a)  mucous 
or  central  cells,  which  are 
transparent  columnar  cells 
with  nuclei  near  the  base- 
ment membrane.  The  cell 
substance  is  made  up  of  a 
fine  network,  which  in  the 


resting    state 


Fig.  168. — From  a  section  through  a  mucous  rjland 
in  a  quiescent  state.  The  alveoli  are  lined  with 
transparent  mucous  cells,  and  outside  these 
are  the  demilunes  of  Heidenhain.  The  cells 
should  have  been  represented  as  more  or  less 
granular.     (Heidenhain.) 

contains    a 

transparent  substance  called  mucigen,  during  which  the  cell  does 
not  stain  well  wTith  logwrood  (fig.  168).  When  the  gland  is  secret- 
ing, mucigen  is  converted  into  mucin,  and  the  cells  swrell  up,  appear 
more  transparent,  and  stain  deeply  in  logwrood  (fig.  169).  During 
rest,  the  cells  become  smaller  and  more  granular  from  having 
discharged  their  contents,  and  the  nuclei  appear  more  distinct. 
(b)  Semilunes  of  Heidenhain  (fig.  168),  which  are  crescentic  masses 
of  granular  parietal  cells  found  here  and  there  between  the 
basement  membrane  and  the  central  cells.  These  cells  are  small, 
and  have  a  very  dense  reticulum,  the  nuclei  are  spherical,  and 
increase   in  size  during   secretion.      In  the   mucous  gland  there 


282  DIGESTION.  [chap.  viii. 

.  -  me  large  tubes,  lined  with  large  transparent  central  cells,  and 
have  besides  a  few  granular  parietal  cells;  other  small  tubes  are 
lined  with  small  granular  parietal  cells  alone;  and  a  third  variety 

are  lined  equally  with  each  kind 
-■gggt-:  --■  '-  °f  cell.     (3)  In  the  muco-sali- 

vary  or  mixed  glands,   as  the 
^^■^^^■BSH^^R       human     submaxillary     gland, 

part  of  the  gland  presents  the 
structure  of  the  mucous  gland, 
whilst  the  remainder  has  that 
of  the  salivary  glands  proper. 

Nerves  and  blood-vessels. — 
Nerves  of  large  size  are  found 
in    the    salivary   glands,   they 

Fig.  169. — A  part  0/ a  section  through  a  mucotis  .  " 

latum,     are  contained  in  the  connective 

The  alveoli  are  lined  with  small  granular         .  _    .         ,         ,.        .       .       .. 

cells.     Lavdovski.)  tissue  of  the  alveoli  principally, 

and  in  certain  glands,  especi- 
ally in  the  dog,  are  provided  with  ganglia.  Some  nerves  have 
special  endings  in  Pacinian  corpuscles,  some  supply  the  blood- 
vessels, and  others,  according  to  Pfliiger,  penetrate  the  basement 
membrane  of  the  alveoli  and  enter  the  salivary  cells. 

The  blood-vessels  form  a  dense  capillary  network  around  the 
ducts  of  the  alveoli,  being  carried  in  by  the  fibrous  trabecular 
between  the  alveoli,  in  which  also  begin  the  lymphatics  by  lacunar 
spaces. 

Saliva. — Saliva,  as  it  commonly  flows  from  the  mouth,  is 
mixed  with  the  secretion  of  the  mucous  [/lands,  and  often  with  air 
bubbles,  which,  being  retained  by  its  viscidity,  make  it  frothy. 
When  obtained  from  the  parotid  ducts,  and  free  from  mucus, 
saliva  is  a  transparent  watery  fluid,  the  specific  gravity  of  which 
varies  from  1004  to  1008,  and  in  which,  when  examined  with  the 
microscope,  are  found  floating  a  number  of  minute  particles, 
derived  from  the  secreting  ducts  and  vesicles  of  the  glands.  In 
the  impure  or  mixed  saliva  are  found,  besides  these  particles, 
numerous  epithelial  scales  separated  from  the  surface  of  the 
mucous  membrane  of  the  mouth  and  tongue,  and  the  so-called 
salivary  corpuscles,  discharged  probably  from  the  mucous  glands 
of  the  mouth  and  the  tonsils,  which,  when  the  saliva  is  collected 
in  a  deep  vessel,  and  left  at  rest,  subside  in  the  form  of  a  white 


CHAP,  viii.]  SALIVA.  283 

opaque  matter.  Leaving  the  supernatant  salivary  fluid  transparent 
and  colourless,  or  with  a  pale  bluish-grey  tint.  In  reaction,  the 
saliva,  when  first  Becreted  appears  to  be  always  alkaline.     During 

Easting,  the  saliva,  although  secreted  alkaline,  shortly  becomes 
neutral  ;  and  it  docs  BO  especially  when  secreted  slowly  and 
allowed  to  mix;  with  the  acid  mucus  of  the  mouth,  by  which  its 
alkaline  reaction  is  neutralized. 

Chemical  Composition  of  Mixed  Saliva  (Frerichs). 

Water        .         .         .         .     «    .         .         .     994*10 
Solids 5-90 


Ptyalin 1*41 

Fat 007 

epithelium  and  Proteids  (including 
Serum-Albumin,  Globulin.  Mucin, 
&c.) 2*13 

Salts  :— 


Potassium  Sulpho-Cyanate 
Sodium  Phosphate 
Calcium  P'hosphatc  . 
Magnesium  Phosphate . 
Sodium  Chloride 
Potassium  Chloride 


2-29 


5'90 

The  presence  of  potassium  sulphocyanate  (or  tltioajanate) 
(CN  K  S)  in  saliva,  may  be  shown  by  the  blood-red  colouration 
which  the  fluid  gives  with  a  solution  of  ferric  chloride  (Fe.2CL6), 
and  which  is  bleached  on  the  addition  of  a  solution  of  mercuric 
chloride  (HgCL). 

Rate  of  Secretion  and  Quantity. — The  rate  at  which  saliva 
is  secreted  is  subject  to  considerable  variation.  When  the  tongue 
and  muscles  concerned  in  mastication  are  at  rest,  and  the  nerves  of 
the  mouth  are  subject  to  no  unusual  stimulus,  the  quantity  secreted 
is  not  more  than  sufficient,  with  the  mucus,  to  keep  the  mouth 
moist.     During  actual  secretion  the  flow  is  much  accelerated. 

The  quantity  secreted  in  twenty-four  hours  varies ;  its  average 
amount  is  probably  from  1  to  3  pints  (1  to  2  litres). 

Uses  of  Saliva. — The  purposes  served  by  saliva  are  (1)  me- 
chanical and  (2)  chemical.  I.  Mechanical. — (1)  It  keeps  the 
mouth  in  a  due  condition  of  moisture,  facilitating  the  movements 
of  the  tongue  in  speaking,  and  the  mastication  of  food.     (2)  It 


284  DIGESTION.  [chap.  viii. 

serves  also  in  dissolving  sapid  substances,  and  rendering  them 
capable  of  exciting  the  nerves  of  taste.  But  the  principal  me- 
chanical purpose  of  the  saliva  is,  (3)  that  by  mixing  with  the  food 
during  mastication,  it  makes  it  a  soft  pulpy  mass,  such  as  may  be 
easily  swallowed.  To  this  purpose  the  saliva  is  adapted  both  by 
quantity  and  quality.  For,  speaking  generally,  the  quantity 
secreted  during  feeding  is  in  direct  proportion  to  the  dryness  and 
hardness  of  the  food.  The  quality  of  saliva  is  equally  adapted  to 
this  end.  It  is  easy  to  see  how  much  more  readily  it  mixes  with 
most  kinds  of  food  than  water  alone  does ;  and  the  saliva  from  the 
parotid,  labial,  and  other  small  glands,  being  more  aqueous  than 
the  rest,  is  that  which  is  chiefly  hr  aided  and  mixed  with  the  food 
in  mastication  ;  while  the  more  viscid  mucous  secretion  of  the 
submaxillary,  palatine,  and  tonsillitic  glands  is  spread  over  the 
surface  of  the  softened  mass,  to  enable  it  to  slide  more  easily 
through  the  fauces  and  oesophagus.  II.  Chemical. — Saliva  has 
the  power  of  converting  starch  into  glucose  or  grape-sugar.  When 
saliva,  or  a  portion  of  a  salivary  gland,  is  added  to  starch  paste  in 
a  test-tube,  and  the  mixture  kept  at  a  temperature  of  ioo°  F. 
(3  7  "8°  C),  the  starch  is  very  rapidly  transformed  into  grape-sugar. 
There  is  an  intermediate  stage  in  which  a  part  or  the  whole  of  the 
starch  becomes  dextrin. 

Test  for  Glucose. — In  such  an  experiment  the  presence  of  sugar  is  at 
once  discovered  by  the  application  of  Trommer's  test,  which  consists  in  the 
addition  of  a  drop  or  two  of  a  solution  of  copper  sulphate,  followed  by  a 
larger  quantity  of  caustic  potash.  "When  the  liquid  is  boiled,  an  orange-red 
precipitate  of  copper  suboxide  indicates  the  presence  of  sugar ;  and  when 
common  raw  starch  is  masticated  and  mingled  with  saliva,  and  kept  with  it 
at  a  temperature  of  900  or  ico°  F.  (30° — 37'8°  C),  the  starch-grains  are 
cracked  or  eroded,  and  their  contents  are  transformed  in  the  same  manner 
as  the  starch-paste. 

Saliva  from  the  parotid  is  less  viscid,  less  alkaline,  clearer,  and 
more  watery  than  that  from  the  submaxillary.  It  has,  moreover, 
a  less  powerful  action  on  starch.  Sublingual  saliva  is  the  most 
viscid,  and  contains  more  solids  than  either  of  the  other  two,  but 
does  not  appear  to  be  so  powerful  in  its  action. 

The  salivary  glands  of  children  do  not  become  functionally  active  till  the 
age  of  4  to  6  months,  and  hence  the  bad  effect  of  feeding  them  before  this 
age  on  starchy  food,  corn-flour,  &c,  which  they  are  unable  to  render  soluble 
and  capable  of  absorption.' 


ni.u'.  viii.]  ACTION     OF    SALIVA.  285 

Action  of  Saliva  on  Starch. — This  action  is  due  to  the  pre- 
sence in  the  saliva  of  the  body  called  ptyalin.  It  is  a  nitrogenous 
body,  and  belongs  to  the  order  of  ferments,  which  are  bodies  who 
exact  chemical  composition  is  unknown,  and  which  .arc  capable  of 
producing  by  their  presence  changes  in  other  bodies,  without 
themselves  undergoing  change.  Ptyalin  is  called  a  hydrolytic 
ferment,  that  is  to  say,  it  acts  by  adding  a  molecule  of  water  to 
the  body  changed.     The  reaction  is  supposed  to  be  as  follows  : 

3  C0HloO5  +  3  H20  =  C0H1200  +  2  (C0HloO5)  +  2  II20  =  3  C6H12O0. 
Starch      +  Water      Glucose  Dextrin  Glucose. 

But  it  is  not  unlikely  that  the  action  is  by  no  means  so  simple. 
In  the  first  place,  recent  observers  believe  that  a  molecule  of  starch 
must  be  represented  by  a  much  more  complex  formula ;  next, 
that  the  stages  in  the  reaction  are  more  numerous  and  extensive  ; 
and  thirdly,  that  the  product  of  the  reaction  is  not  true  glucose, 
but  maltose.  Maltose  is  a  sugar  more  akin  to  cane-  than  grape- 
sugar,  of  very  little  sweetening  power,  and  with  less  reducing 
power  over  copper  salts.     Its  formula  is  CiaH220lx. 

The  action  of  saliva  on  starch  is  facilitated  by  :  (a)  Moderate 
heat,  about  ioo°  F.  (37*8°  C).  (b)  A  slightly  alkaline  medium. 
(c)  Removal  of  the  changed  material  from  time  to  time.  Its 
action  is  retarded  by :  (a)  Cold  ;  a  temperature  of  320  F.  (o°  C.) 
stops  it  for  a  time,  but  does  not  destroy  it,  whereas  a  high  tem- 
perature above  1400  F.  (6o°  C.)  destroys  it.  (6)  Acids  or  strong 
alkalies  either  delay  or  stop  the  action  altogether,  (c)  Presence 
of  too  much  of  the  changed  material.  Ptyalin,  in  that  it  converts 
starch  into  sugar,  is  an  amylolytic  ferment. 

Starch  appears  to  be  the  only  principle  of  food  upon  which 
saliva  acts  chemically  :  it  has  no  apparent  influence  on  any  of  the 
other  ternary  principles,  such  as  sugar,  gum,  cellulose,  or  on  fit, 
and  seems  to  be  equally  destitute  of  power  over  albuminous  and 
gelatinous  substances. 

Influence  of  the  Nervous  System. — The  secretion  of  saliva 
is  under  the  control  of  the  nervous  system.  It  is  a  reflex  action, 
and  in  ordinary  conditions  is  excited  by  the  stimulation  of  the 
peripheral  branches  of  two  nerves,  viz.,  the  gustatory  or  lingual 
branch  of  the  inferior  maxillary  division  of  the  fifth  nerve,  and  the 
glossopharyngeal  part  of  the  eighth  pair  of  nerves,  which  are  dis- 
tributed to  the  mucous  membrane  of  the  tongue  and  pharynx. 


286  DIGESTION.  [chap.  viii. 

The  stimulation  occurs  on  the  introduction  of  sapid  substances  into 
the  mouth,  and  the  secretion  is  brought  about  in  the  following  way. 
From  the  terminations  of  these  sensory  nerves  in  the  mucous 
membrane  an  impression  is  conveyed  upwards  (afferent)  to  the 
special  nerve  centre  situated  in  the  medulla,  which  controls  the 
process,  and  by  it  is  reflected  to  certain  nerves  supplied  to  the 
salivary  glands,  which  will  be  presently  indicated.  In  other 
words,  the  centre,  stimulated  to  action  by  the  sensory  impressions 
carried  to  it,  sends  out  impulses  along  efferent  or  secretory  nerves 
supplied  to  the  salivary  glands,  which  cause  the  saliva  to  be 
secreted  by  and  discharged  from  the  gland  cells.  Other  stimuli, 
however,  besides  that  of  the  food,  and  other  sensory  nerves  besides 
those  mentioned,  may  produce  reflexly  the  same  effects.  Saliva 
may  be  caused  to  flow  by  irritation  of  the  mucous  membrane  of 
the  mouth  with  mechanical,  chemical,  electrical,  or  thermal 
stimuli,  also  by  the  irritation  of  the  mucous  membrane  of  the 
stomach  in  some  way,  as  in  nausea,  which  precedes  vomiting,  when 
some  of  the  peripheral  fibres  of  the  vagi  are  irritated.  Stimulation 
of  the  olfactory  nerves  by  smell  of  food,  of  the  optic  nerves  by  the 
sight  of  it,  and  of  the  auditory  nerves  by  the  sounds  which  are 
known  by  experience  to  accompany  the  preparation  of  a  meal,  may 
also,  in  the  hungry,  stimulate  the  nerve  centre  to  action.  In  addi- 
tion to  these,  as  a  secretion  of  saliva  follows  the  movement  of  the 
muscles  of  mastication,  it  may  be  assumed  that  this  movement 
stimulates  the  secreting  nerve  fibres  of  the  gland,  directly  or 
reflexly.  From  the  fact  that  the  flow  of  saliva  may  be  increased 
or  diminished  by  mental  emotions,  it  is  evident  that  impressions 
from  the  cerebrum  also  are  capable  of  stimulating  the  centre  to 
action  or  of  inhibiting  its  action. 

Secretion  may  be  excited  by  direct  stimulation  of  the  centre  in 
the  medulla. 

A.  On  the  Submaxillary  Gland. — The  submaxillary  gland  has 
been  the  gland  chiefly  employed  foi*  the  purpose  of  experimentally 
demonstrating  the  influence  of  the  nervous  system  upon  the  secre- 
tion of  saliva,  because  of  the  comparative  facility  with  which,  with 
its  blood-vessels  and  nerves,  it  may  be  exposed  to  view  in  the  dog, 
rabbit,  and  other  animals.  The  chief  nerves  supplied  to  the  gland 
are  :  (i)  the  chorda  tympani,  a  branch  given  off  from  the  facial 
portio  dura  of  the  seventh  pair  of  nerves),  in  the  canal  through 


coup,  viii.]  SECRETION    OF    SALIYA.  2.S7 

which  it  passes  in  the  temporal  bone,  in  it-  passage  from  the 
interior  of  the  skull  to  the  face;  and  (2)  branches  of  the  sympa- 
thetic nerve  from  the  plexus  around  the  facial  artery  and 
branches  to  the  gland.  The  chorda  ( fiu.  170,  eh.  t),  after  quitting 
the  temporal  bone,  passes  downwards  and  forwards,  under  c 
the  externa]  pterygoid  muscle,  and  joins  at  an  acute  angle  the 
lingual  or  gustatory  uerve,  proceeds  with  it  for  a  short  distance, 
and  then  passes  along  the  submaxillary  gland  duct  (fig.  170,  sm.d.), 
t<>  which  it  is  distributed,  giving  branches  to  the  submaxillary 
ganglion  (fig.  170,  sm.  ///.),  and  sending  others  to  terminate  in 
the  superficial  muscle  of  the  tongue.  If  this  nerve  be  expos 
and  divided  anywhere  in  its  course  from  its  exit  from  the  skull  to 
the  gland,  the  secretion,  if  the  gland  be  in  action,  is  arrested,  and 
no  stimulation  either  of  the  lingual  or  of  the  glossopharyngeal 
will  produce  a  flow  of  saliva.  But  if  the  peripheral  end  of 
the  divided  nerve  be  stimulated,  an  abundant  secretion  of  saliva 
ensues,  and  the  blood  supply  is  enormously  increased,  the  arteries 
being  dilated.  The  veins  even  pulsate,  and  the  blood  contained 
within  them  is  more  arterial  than  venous  in  character. 

When,  on  the  other  hand,  the  stimulus  is  applied  to  the  sympa- 
thetic filaments  (mere  division  producing  no  apparent  effect), 
the  arteries  contract,  and  the  blood  stream  is  in  consequence 
much  diminished  ;  and  from  the  veins,  when  opened,  there 
escapes  only  a  sluggish  stream  of  dark  blood.  The  saliva,  instead 
of  being  abundant  and  watery,  becomes  scanty  and  tenacious.  If 
both  chorda  tympani  and  sympathetic  branches  be  divided,  the 
gland,  released  from  nervous  control,  secretes  continuously  and 
abundantly  {paralytic  secretion). 

The  abundant  secretion  of  saliva,  which  follows  stimulation  of 
the  chorda  tympani,  is  not  merely  the  result  of  a  filtration  of  fluid 
from  the  blood-vessels,  in  consequence  of  the  largely  increased  cir- 
culation through  them.  This  is  proved  by  the  fact  that,  when 
the  main  duct  is  obstructed,  the  pressure  within  may  considerably 
exceed  the  blood-pressure  in  the  arteries,  and  also  that  when  into 
the  veins  of  the  animal  experimented  upon  some  atropin  has  been 
previously  injected,  stimulation  of  the  peripheral  end  of  the 
divided  chorda  produces  all  the  vascular  effects  as  before,  without 
any  secretion  of  saliva  accompanying  them.  Again,  if  an  animals 
head  be  cut  off,  and  the  chorda  be  rapidly  exposed  and  stimulated 


2S8 


DIGESTION. 


[CHAP.  VIII. 


with  an  interrupted  current,  a  secretion  of  saliva  ensues  for  a 
short  time,  although  the  blood  supply  is  necessarily  absent. 
These  experiments  serve  to  prove  that  the  chorda  contains  two 
sets  of  nerve  fibres,  one  set  (yaso-dilator)  which,  when  stimulated, 
act  upon  a  local  vaso-motor  centre  for  regulating  the  blood  supply, 
inhibiting  its  action,  and  causing  the  vessels  to  dilate,  and  so  pro- 
ducing an  increased  supply  of  blood  to  the  gland  ■  while  another 
set,  which  are  paralyzed  by  injection  of  atropin,  directly  stimulate 


Fi°\  170. — Diagrammatic  representation  of  the  submaxillary  gland  0/  the  dog  tvith  its  nerves  and 
°  blood-vessels.  (This  is  not  intended  to  illustrate  the  exact  anatomical  relations  of  the 
several  structures.)  sm.  gld.,  the  submaxillary  gland  into  the  duct  (s7n.  d.),  of  which 
a  cannula  has  been  tied.  The  sublingual  gland  and  duct  are  not  shown.  n.L,  n.  I'.,  the 
lingual  or  gustatory  nerve  ;  eh.  t.,  eh.  t'.,  the  chorda  tympani  proceeding  from  the  facial 
nerve,  becoming  conjoined  with  the  lingual  at  n.  7'.,  and  afterwards  diverging  and 
passing  to  the  gland  along  the  duct;  sm.  gl.,  submaxillary  ganglion  with  its  roots; 
n.L,  the  lingual  nerve  proceeding  to  the  tongue;  a.  car.,  the  carotid  artery,  two 
branches  of  which,  a.  am.  n.  and  /•.  sm.  p.,  pass  to  the  anterior  and  posterior  parts  of 
the  gland  ;  v.  sm.,  the  anterior  and  posterior  veins  from  the  gland  ending  in  v.j.,  the 
jugular  vein  ;  r.  sym.,  the  conjoined  vagus  and  sympathetic  trunks  ;  gl.  cer.  s.,  the 
superior-cervical  ganglion,  two  branches  of  which  fomnng  a  plexus,  a./.,  over  the  facial 
artery  are  distributed  [n.  sym.  sm.)  along  the  two  glandular  arteries  to  the  anterior 
and  posterior  portion  of  the  gland.  The  arrows  indicate  the  direction  taken  by  the 
nervous  impulses  ;  during  reflex  stimulations  of  the  gland  they  ascend  to  the  brain  by 
the  lingual  and  descend  by  the  chorda  tympani.     (M.  Foster. ) 


the  cells  themselves  to  activity,  whereby  they  secrete  and  dis- 
charge the  constituents  of  the  saliva  which  they  produce.  These 
latter  fibres  very  possibly  terminate  in  the  salivary  cells  them- 
selves. If,  on  the  other  hand,  the  sympathetic  fibres  be  divided, 
stimulation  of  the  tongue  by  sapid  substances,  or  of  the  trunk  of 
the  lingual,  or  of  the  glosso-pharyngeal  continues  to  produce  a  flow 


.hat.  mil]     IM-I.l'K.WK    OF    THE    SERYOU8    8Y8TEM. 

of  saliva.     From  these  experiment  that  the  chorda 

tympani  nerve  is  the  principal  nerve  through  which  efferent  im- 
pulses proceed  from  the  cenl      bo  excite  the  secretion  of  this  gland. 
The  sympathetic  fibres  appear  to  act  principally  as  a  vaso-con- 

strictor   nerve,  and  t<>  exult  the  action  of  the  local   v.. 
centres.     The  sympathetic  is  more  powerful  in  this  direction  than 
the  chorda.     There   is   not   sufficient   evidence  in   favour  of  the 
belief  that  the  submaxillary  ganglion   is  ever   the  nerve  centre 
which  controls  the  secretion  of  the  submaxillarv  gland. 

- 

/>.  On  the  Parotid  Gland. — The  nerves  which  influence  secre- 
tion in  the  parotid  gland  are  branches  of  the  facial  (lesser  super- 
ficial petrosal)  and  of  the  sympathetic.  The  former  nerve,  after 
passing  through  the  otic  ganglion,  joins  the  auriculo-temporal 
branch  of  the  fifth  cerebral  nerve,  and,  with  it.  is  distributed  to 
the  gland.  The  nerves  by  which  the  stimulus  ordinarily  exciting 
secretion  is  conveyed  to  the  medulla  oblongata,  are.  as  in  the 
of  the  submaxillary  gland,  the  fifth,  and  the  glossopharyn- 
geal The  pneumogastric  nerves  convey  a  further  stimulus  to  the 
tion  of  saliva,  when  food  has  entered  the  stomach  ;  the  nerve 
centre  is  the  same  as  in  the  case  of  the  submaxillary  gland. 

Changes  in  the  Gland  Cells. — -The  method  by  which  the 
salivary  cells  produce  the  secretion  of  saliva  appeal's  to  be  divided 
into  two  stages,  which  differ  somewhat  according  to  the  class 
to  which  the  gland  belongs,  viz.,  (r)  the  true  salivary,  or 
(2)  the  mucous  type.  In  the  former  case,  it  has  been  noticed,  as 
has  been  already  described  (p.  281),  that  during  the  rest  which 
follows  an  active  secretion  the  lumen  of  the  alveoli  becomes 
smaller,  the  gland  cells  larger,  and  very  granular.  During  secre- 
tion the  alveoli  and  their  cells  become  smaller,  and  the  granular 
appearance  in  the  latter  to  a  considerable  extent  disappears,  and 
at  the  end  of  secretion,  the  granules  are  confined  to  the  inner 
part  of  the  cell  nearest  to  the  lumen,  which  is  now  quite  distinct 
(fig.  171). 

It  is  supposed  from  these  appearances  that  the  first  stage  in  the 
act  of  secretion  consists  in  the  protoplasm  of  the  salivary  cell 
taking  up  from  the  lymph  certain  materials  from  which  it  manu- 
factures the  elements  of  its  own  secretion,  and  which  are  stored 
up  in  the  form  of  granules  in  the  cell  during  rest,  the  second 
ting  of  the  actual  discharge  of  these  granules,  with  or 


290 


DIGESTION. 


[chap.  VIII. 


without  previous  change.  The  granules  are  taken  to  represent 
the  chief  substance  of  the  salivary  secretion,  i.e.,  the  ferment 
ptyalin.  In  the  case  of  the  submaxillary  gland  of  the  dog,  at  any 
rate,  the  sympathetic  nerve-fibres  appear  to  have  to  do  with  the 


Fig.  171. — Alveoli  of  true  salivary  gland.    A,  at  rest ;  B,  in  the  first  stage  of  secretion ; 
C,  after  prolonged  secretion.     (Langley.) 

first  stage  of  the  process,  and  when  stimulated  the  protoplasm  is 
extremely  active  in  manufacturing  the  granules,  whereas  the 
chorda  tympani  is  concerned  in  the  production  of  the  second  act, 
the  actual  discharge  of  the  materials  of  secretion,  together  with 
a  considerable  amount  of  fluid,  the  latter  being  an  actual  secretion 
by  the  protoplasm,  as  it  ceases  to  occur  when  atropin  has  been 
subcutaneously  injected. 

In  the  mucous-secreting  gland,  the  changes  in  the  cells  during 
secretion  have  been  already  spoken  of  (p.  281).  They  consist  in 
the  gradual  secretion  by  the  protoplasm  of  the  cell  of  a  substance 
called  mucigen,  which  is  converted  into  mucin,  and  discharged  on 
secretion  into  the  canal  of  the  alveoli.  The  mucigen  is,  for  the 
most  part,  collected  into  the  inner  part  of  the  cells  during  rest, 
pressing  the  nucleus  and  the  small  portion  of  the  protoplasm 
which  remains,  against  the  limiting  membrane  of  the  alveoli. 

The  process  of  secretion  in  the  salivary  glands  is  identical  with 
that  of  glands  in  general;  the  cells  which  line  the  ultimate 
branches  of  the  ducts  being  the  agents  by  which  the  special  con- 
stituents of  the  saliva  are  formed.  The  materials  which  they  have 
incorporated  with  themselves  are  almost  at  once  given  up  again, 
in  the  form  of  a  fluid  (secretion),  which  escapes  from  the  ducts  of 
the  gland  ;  and  the  cells,  themselves,  undergo  disintegration, — 
again  to  be  renewed,  in  the  intervals  of  the  active  exercise  of  their 
functions.     The   source   whence   the   cells  obtain   the   materials 


chap,  viii.]  THE    pharynx. 


291 


of  their  secretion,  is  the  blood,  <>r,  to  Bpeak  more  accurately,  the 
plasma,  which  is  filtered  off  from  the  circulating  blood  into  the 
interstices  of  the  glands  as  of  all  living  textures. 


The  Pharynx. 

That  portion  of  the  alimentary  canal  which  intervenes  between 
the  mouth  and  the  oesophagus  is  termed  the  Pharynx  (fig.  165). 
It  will  suffice  here  to  mention  that  it  is  constructed  of  a  series 
of  three  muscles  with  striated  fibres  (con- 
strictors), which  are  covered  by  a  thin 
fascia  externally,  and  are  lined  internally 
by  a  strong  faseia  (pharyngeal  aponeurosis), 
on  the  inner  aspect  of  which  is  areolar 
(submucous)  tissue  and  mucous  membrane, 
continuous  with  that  of  the  mouth,  and,  as 
regards  the  part  concerned  in  swallowing, 
is  identical  with  it  in  general  structure. 
The  epithelium  of  this  part  of  the  pha-  Fig.  T72.—Lhi(piai  foUich  or 
rynx,  like  that  of  the  mouth,  is  stratified         mucous  "memSanl^th 

onrl   en n. -.m mi «  its  papillee  ;    h,  lymphoid 

ana  Squamous.  tissue,  with  several  lym- 

The    pharynx    is    well    supplied    with         phoidsacs.    (Frey.) 
mucous  glands  (fig.  174). 

The  Tonsils. — Between  the  anterior  and  posterior  arches  of 
the  soft  palate  are  situated  the  Tonsils,  one  on  each  side.  A 
tonsil  consists  of  an  elevation  of  the  mucous  membrane  presenting 
12  to  15  orifices,  which  lead  into  crypts  or  recesses,  in  the  walls 
of  Avhich  are  placed  nodules  of  adenoid  or  lymphoid  tissue  (fig. 
173).  These  nodules  are  enveloped  in  a  less  dense  adenoid  tissue 
which  reaches  the  mucous  surface.  The  surface  is  covered  with 
stratified  squamous  epithelium,  and  the  subepithelial  or  mucous 
membrane  proper  may  present  rudimentary  papillae  formed  of 
adenoid  tissue.  The  tonsil  is  bounded  by  a  fibrous  capsule  (fig. 
173,  e).  Into  the  crypts  open  a  number  of  ducts  of  mucous 
glands. 

The  viscid  secretion  which  exudes  from  the  tonsils  serves  to 
lubricate  the  bolus  of  food  as  it  passes  them  in  the  second  part  1  >f 
the  act  of  deglutition. 

D  2 


292 


DIGESTION. 


[CHAP.  VIII. 


The  (Esophagus  or  Gullet. 

The  (Esophagus  or   Gullet  (fig.  165),  the  narrowest  portion  of 
the  alimentary  canal,  is  a  muscular  and  mucous  tube,  nine  or  ten 


Fig.  173. —  Vertical  section  through  a  erupt  of  the  human  tonsil,  o,  entrance  to  the  crypt, 
•which  is  divided  below  by  the  elevation  -which  does  not  quite  reach  the  surface ; 
l>,  stratified  epithelium ;  c,  masses  of  adenoid  tissue ;  d,  mucous  glands  cut  across ; 
e,  fibrous  capsule.     (V.  D.  Harris.) 


inches  in  length,  which  extends  from  the  lower  end  of  the  pharynx 
to  the  cardiac  orifice  of  the  stomach. 

Structure. — The  oesophagus  is  made  up  of  three  coats — viz., 
the  outer,  muscular;  the  middle,  submucous;  and  the  inner, 
mucous.  The  muscular  coat  (fig.  175,  </  and  i)  is  covered  exter- 
nally by  a  varying  amount  of  loose  fibrous  tissue.  It  is  composed 
of  two  layers  of  fibres,  the  outer  being  arranged  longitudinally, 
and  the  inner  circularly.  At  the  upper  part  of  the  oesophagus  this 
coat  is  made  up  principally  of  striated  muscle  fibres,  as  they  are 
continuous  with  the  constrictor  muscles  of  the  pharynx ;  but  lower 
down  the  unstriated  fibres  become  more  and  more  numerous,  and 
towards  the  end  of  the  tube  form  the  entire  coat.  The  muscular 
coat  is  connected  with  the  mucous  coat  by  a  more  or  less  de- 
veloped layer  of  areolar  tissue,  which  forms  the  submucous  coat 
(fig.  175,/),  in  which  is  contained  in  the  lower  half  or  third  of 


ch  IP.  \ni. J    STRUCTURE  OF  THE  (ESOPHAGUS. 


293 


the  tube  many  mucous  glands,  the  ducts  of  which,  passing  through 
tin-  nine. mis  membrane  (fig.  175,'')  open  on  its  Burface.  Separ- 
ating this  coat    from    the    mucous   membrane    proper  is  a   TOll- 


Fig.  174. — Section  of  a  mucous  gland  from  the  tongue.  A,  opening  of  the  duct  on  the  free 
surface ;  C,  basement  membrane  with  nuclei ;  B,  flattened  epithelial  cells  lining  duct. 
The  duct  divides  into  several  branches,  which  are  convoluted  and  end  blindly,  being- 
lined  throughout  by  columnar  epithelium.  D,  lumen  of  one  of  the  tubuli  of  the  gland, 
x  90.     (Klein  and  Noble  Smith.) 


developed  layer  of  longitudinal,  unstriated  muscle  (d),  called  the 
muscularis  mucosce.  The  mucous  membrane  is  composed  of  a 
closely  felted  meshwork  of  fine  connective  tissue,  which,  towards 
the  surface,  is  elevated  into  rudimentary  papillae.  It  is  covered 
with  a  stratified  epithelium,  of  which  the  most  superficial  layers 
are  squamous.  The  epithelium  is  arranged  upon  a  basement 
membrane. 

In  newly-born  children  the  mucous  membrane  exhibits,  in 
many  parts,  the  structure  of  lymphoid  tissue  (Klein). 

Blood-  and  lymph-vessels,  and  nerves,  are  distributed  in   the 


294 


DIGESTION. 


[CHAP.  VIII. 


walls  of  the  oesophagus.     Between  the  outer  and  inner  layers  of 
the  muscular  coat,  nerve-ganglia  of  Auerbach  are  also  found. 


Fig.  175. — Longitudinal  section  of  oesophagus  of  a  dog  towards  the  loiver  end.  a,  stratified 
epithelium  of  the  mucous  membrane  ;  b,  mucous  membrane  proper  ;  c,  duct  of  mucous 
gland ;  d,  muscularis  mucosa  ;  e,  mucous  glands  ;  /,  submucous  coat ;  g,  circular 
muscular  layer;  h,  intermuscular  layer,  in  which  is  contained  the  ganglion  cells  of 
Auerbach;  S",  longitudinal  muscular  layer;  I;  outside  investment  of  fibrous  tissue. 
X  100.     (V.  D.  Harris. 


Deglutition  or  Swallowing. 

When  properly  masticated,  the  food  is  transmitted  in  successive 
portions  to  the  stomach  by  the  act  of  deglutition  or  swallowing. 
This,  for  the  purpose  of  description,  may  be  divided  into  three  acts. 
In  the  first,  particles  of  food  collected  to  a  morsel  are  made  to  glide 
between  the  surface  of  the  tongue  and  the  palatine  arch,  till  they 
have  passed  the  anterior  arch  of  the  fauces ;  in  the  second,  the 
morsel  is  carried  through  the  pharynx ;  and  in  the  third,  it 
reaches  the  stomach  through  the  oesophagus.  These  three  acts 
follow  each  other  rapidly.  (1.)  The  first  act  of  deglutition  may 
be  voluntary,  although  it  is  usually  performed  unconsciously  ;  the 


chap,  vim.]  DEGLUTITION.  295 

morsel  of  food,  when  sufficiently  masticated,  being  pressed  between 
the  tongue  and    palate,  by   the  agency   of   the  muscles    of    the 

former,  in  such  a  manner  us  t<>  force  it  back  to  the  entrance  of 
the    pharynx.      (2.)    The    second    act    is    the    most   complicated, 
because  the  food  must  pass  bythe  posterior  orifice  of  the  oose  and 
the  upper  opening  of  the  larynx  without  touching  them.     When 
it  has  been   brought,  by  the  first   act,  between  the  anterior  arches 
of  the  palate,  it  is  moved  onwards  by  the  movement  of  the  tongue 
backwards,  and  by  the  muscles  of  the  anterior  arches  contracting 
on  it  and  then  behind  it.     The  root  of  the  tongue  being  retracted, 
and   the  larynx  being  raised  with  the   pharynx    and  carried   for- 
wards under  the  base  of  the  tongue,  the  epiglottis  is  pressed  over 
the  upper  opening  of  the  larynx,  and  the  morsel  glides  past  it ; 
the  closure  of  the  glottis  being  additionally  secured  by  the  simul- 
taneous contraction  of  its  own  muscles  :  so  that,  even  when  the 
epiglottis  is  destroyed,  there  is  little  danger  of  food  or  drink  pass- 
ing into  the  larynx  so  long  as  its  muscles  can  act  freely.     At  the 
same  time,  the  raising  of  the  soft  palate,  so  that  its  posterior  edge 
touches  the  back  part  of  the  pharynx,  and  the  approximation  of 
the  sides  of  the  posterior  palatine  arch,  which  move  quickly  in- 
wards like  side  curtains,  close  the  passage  into  the  upper  part  of 
the  pharynx  and  the  posterior  nares,  and  form  an  inclined  plane, 
along  the  under  surface  of  which  the  morsel  descends ;  then  the 
pharynx,  raised  up  to  receive  it,  in  its  turn  contracts,  and  forces 
it  onwards  into  the  oesophagus.      (3.)  In  the  third  act,  in  which 
the  food  passes  through  the  oesophagus,  every  part  of  that  tube, 
as  it  receives  the  morsel  and  is  dilated  by  it,  is  stimulated  to  con- 
tract :  hence  an  undulatory  contraction  of  the  oesophagus,  which 
is    easily  observable  in  horses   while   drinking,   proceeds   rapidly 
along  the  tube.     It  is  only  when  the  morsels  swallowed  are  large, 
or  taken  too  quickly  in  succession,  that   the  progressive  contrac- 
tion of  the  oesophagus  is  slow,  and  attended  with  pain.     Division 
of  both  pneumogastric  nerves  paralyses  the  contractile  power  of 
the   oesophagus,    and  food   accordingly  accumulates   in  the   tube. 
The    second    and    third   parts   of  the  act   of  deglutition    are   in- 
voluntary. 

Nerve  Mechanism. — The  nerves  engaged  in  the  reflex  act  of 
deglutition  are  : — sensory,  branches  of  the  fifth  cerebral  supplying 
the    soft    palate;    glosso-pharyngeal,   supplying    the    tongue    and 


296  DIGESTION.  [chap.  vni. 

pharynx  ;  the  superior  laryngeal  branch  of  the  vagus,  supplying 
the  epiglottis  and  the  glottis ;  while  the  motor  fibres  concerned 
are  : — branches  of  the  fifth,  supplying  part  of  the  digastric  and 
mylo-hyoid  muscles,  and  the  muscles  of  mastication ;  the  facial, 
supplying  the  levator  palati ;  the  glosso-pharyngeal,  supplying 
the  muscles  of  the  pharynx  ;  the  vagus,  supplying  the  muscles  of 
the  larynx  through  the  inferior  laryngeal  branch,  and  the  hypo- 
glossal, the  muscles  of  the  tongue.  The  nerve-centre  by  which 
the  muscles  are  harmonised  in  their  action,  is  situate  in  the 
medulla  oblongata.  In  the  movements  of  the  oesophagus,  the 
ganglia  contained  in  its  walls,  with  the  pneuino-gastrics,  are  the 
nerve-structures  chiefly  concerned. 

It  is  important  to  note  that  the  swallowing  both  of  food  and 
drink  is  a  muscular  act,  and  can,  therefore,  take  place  in  opposition 
to  the  force  of  gravity.  Thus,  horses  and  many  other  animals 
habitually  drink  up-hill,  and  the  same  feat  can  be  performed  by 
jugglers. 

The  Stomach. 

In  man  and  those  Mammalia  which  are  provided  with  a  single 
stomach,  it  consists  of  a  dilatation  of  the  alimentary  canal 
placed  between  and  continuous  with  the  oesophagus,  which  enters 
its  larger  or  cardiac  end  on  the  one  hand,  and  the  small  intes- 
tine, which  commences  at  its  narrowed  end  or  pylorus,  on  the 
other.  It  varies  in  shape  and  size  according  to  its  state  of 
distension. 

The  Ruminants  (ox.  sheep,  deer,  &c.)  posse>»  very  complex  stomachs  ;  in 
most  of  them  four  distinct  cavities  are  to  be  distinguished  (fig.  176). 

1.  The  Pavndi  or  Rumen,  a  very  large  cavity  which  occupies  the  cardiac 
end.  and  into  which  large  quantities  of  food  are  in  the  first  instance  swal- 
lowed with  little  or  no  mastication.  2.  The  Reticulum,  or  Honeycomb 
stomach,  so  called  from  the  fact  that  its  mucous  membrane  is  disposed  in  a 
number  of  folds  enclosing  hexagonal  cells.  3.  The  Psalteriwm,  orManyplies, 
in  which  the  mucous  membrane  is  arranged  in  very  prominent  longitudinal 
folds.  4.  Abomasum,  Reed,  or  Rennet,  narrow  and  elongated,  its  mucous 
membrane  being  much  more  highly  vascular  than  that  of  the  other  divisions. 
In  the  process  of  rumination  small  portions  of  the  contents  of  the  rumen  and 
reticulum  are  successively  regurgitated  into  the  mouth,  and  there  thoroughly 
masticated  and  insalivated  (chewing  the  cud)  :  they  are  then  again 
swallowed,  being  this  time  directed  by  a  groove  (which  in  the  figure  is  seen 
running  from  the  lower  end  of  the  a?sophagus)  into  the  manyplies,  and 
thence  into  the  abomasum.     It  will  thus  be  seen  that  the  first  two  stomachs 


•  li  \r.   VIII.] 


Til  I!     STOMACH. 


297 


(paunch  and  reticulum)  have  chiefly  the  mechanical   functions  of  storing 
ami   moistening   (lie   Eodder:    tin'    third    (manyplies)   probably  act-;  as  u 
strainer,  only  allowing  the  finely  divided  portions  "I'  Eood   to  pass  on  into 
the  fourth  stomach,  where  the  gastric  juice  is  Becreted  ami  the  proci 
digestion  carried  on.     The  mucous  membrane  of  the  firs!    three  stomachs 


Fig.  176. — Stomach  0/ sheep.  a>,  oesophagus  ;  Ru,  ramen;  Set,  reticulum ;  Pa,  psalterium, 
or  manyplies;  A,  abomasum ;  Jjk,  duodenum  ;  <j,  gTOove  from  ojsopliag-iis  to  psalte- 
rium.    (Huxley.) 


is  lowly  vascular,  while  that  of  the  fourth  is  pulpy,  glandular,  and  highly 
vascular. 

In  some  other  animals,  as  the  pig,  a  similar  distinction  obtains  between 
the  mucous  membrane  in  different  parts  of  the  stomach. 

In  the  pig  the  glands  in  the  cardiac  end  are  few  and  small,  while  towards 
the  pylorus  they  are  abundant  and  large. 

A  similar  division  of  the  stomach  into  a  cardiac  (receptive)  and  a  pyloric 
(digestive)  part,  foreshadowing  the  complex  stomach  of  ruminants,  is  seen 
in  the  common  rat,  in  which  these  two  divisions  of  the  stomach  are  dis- 
tinguished, not  only  by  the  characters  of  their  lining  membrane,  but  also  by 
a  well-marked  constriction. 

In  birds  the  function  of  mastication  is  performed  by  the  stomach  (gizzard) 
which  in  granivorous  orders,  e.g.  the  common  fowl,  possesses  very  powerful 
muscular  walls  and  a  dense  horny  epithelium. 

Structure. — The  stomach  is  composed  of  four  coats,  called 
respectively — an  external  or  (i)  peritoneal,  (2)  muscular,  (3)  sub- 
mucous, and  (4)  mucous  coat ;  with  blood-vessels,  lymphatics,  and 
nerves  distributed  in  and  between  them. 

(1)  The  peritoneal  coat  has  the  structure  of  serous  membranes  in 
general  (p.  394).  (2)  The  muscular  ami  consists  of  three  separate 
layers  or  sets  of  fibres,  which,  according  to  their  several  direc- 
tions, are  named  the  longitudinal,  circular,  and  oblique.  The 
longitudinal  set  are  the  most  superficial  :  they  are  continuous 
with  the  longitudinal  fibres  of  the  oesophagus,  and  spread  out  in 

diverging  manner  over  the  cardiac  end  and  sides  of  the  stomach. 
They  extend  as   far   as  the  pylorus,  being  especially  distinct  at 


298  DIGESTION.  [chap.  viii. 

the  lesser  or  upper  curvature  of  the  stomach,  along  which  they 
pass  in  several  strong  bands.  The  next  set  are  the  circular  or 
transverse  fibres,  which  more  or  less  completely  encircle  all  parts 
of  the  stomach  ;  they  are  most  abundant  at  the  middle  and  in 
the  pyloric  portion  of  the  organ,  and  form  the  chief  part  of  the 
thick  projecting  ring  of  the  pylorus.  These  fibres  are  not  simple 
circles,  but  form  double  or  fignre-of-8  loops,  the  fibres  intersecting 
very  obliquely.  The  next,  and  consequently  deepest  set  of  fibres, 
are  the  oblique,  continuous  with  the  circular  muscular  fibres  of  the 
oesophagus,  and  having  the  same  double-looped  arrangement  that 
prevails  in  the  preceding  layer :  they  are  comparatively  few  in 
number,  and  are  placed  only  at  the  cardiac  orifice  and  portion  of 
the  stomach,  over  both  surfaces  of  which  they  are  spread,  some 
passing  obliquely  from  left  to  right,  others  from  right  to  left, 
around  the  cardiac  orifice,  to  which,  by  their  interlacing,  they 
form  a  kind  of  sphincter,  continuous  with  that  around  the  lower 
end  of  the  oesophagus.  The  muscular  fibres  of  the  stomach  and 
of  the  intestinal  canal  are  un&triated,  being  composed  of  elongated, 
spindle-shaped  fibre-cells. 

(3)  and  (4)  The  mucous  membrane  of  the  stomach,  which  rests 
upon  a  layer  of  loose  cellular  membrane,  or  submucous  tissue,  is 
smooth,  level,  soft,  and  velvety ;  of  a  pale  pink  colour  during  life, 
and  in  the  contracted  state  thrown  into  numerous,  chiefly  longi- 
tudinal, folds  or  rugae,  which  disappear  when  the  organ  is 
distended. 

The  basis  of  the  mucous  membrane  is  a  fine  connective  tissue, 
which  approaches  closely  in  structure  to  adenoid  tissue  ;  this  tissue 
supports  the  tubular  glands  of  which  the  superficial  and  chief  part 
of  the  mucous  membrane  is  composed,  and  passing  up  between  them 
assists  in  binding  them  together.  Here  and  there  are  to  be  found 
in  this  coat,  immediately  underneath  the  glands,  masses  of  adenoid 
tissue  sufficiently  marked  to  be  termed  by  some  lymphoid  follicles. 
The  glands  are  separated  from  the  rest  of  the  mucous  membrane 
by  a  very  fine  homogeneous  basement  membrane. 

At  the  deepest  part  of  the  mucous  membrane  are  two  layers 
(circular  and  longitudinal)  of  unstriped  muscular  fibres,  called  the 
muscularis  mucosae,  which  separate  the  mucous  membrane  from  the 
scanty  submucous  tissue. 

When  examined  with  a  lens,  the  internal  or  free  surface  of  the 


ohap.  viii.]  GLANDS    OP    THE    BTOMACH.  299 

Btomacfa  presents  a  peculiar  honeycomb  appearance,  produced  l>v 
shallow  polygonal  depressions,  the  diameter  of  which  varies 
generally  from  ...'...th  to  0-,,tli  of  an  inch  ;  but  near  the  pylorus 
Is  as  much  as  1(1ll)th  of  an  Inch.  They  are  separated  by  slightly 
elevated  ridges,  which  sometimes,  (.'specially  in  certain  morbid 
states  <it'  the  stomach,  hear  minute,  narrow  vascular  proces 
which  look  like  villi,  and  have  given  rise  to  the  erroneous  sup- 
position that  the  stomach  has  absorbing  villi,  like  those  of  the 
small  intestines.  In  the  bottom  of  these  little  pits,  and  to  some 
extent  between  them,  minute  openings  are  visible,  which  are  the 
orifices  of  the  ducts  of  perpendicularly  arranged  tubular  glands 
(fig.  177),  imbedded  side  by  side  in  sets  or  bundles,  on  the  sur- 
face of  the  mucous  membrane,  and  composing  nearly  the  whole 
structure. 

Gastric  Glands. — of  these  there  are  two  varieties,  (a)  Peptic, 
(b)  Pyloric  or  Mucous. 

(a)  Peptic  glands  are  found  throughout  the  whole  of  the 
stomach  except  at  the  pylorus.  They  are  arranged  in  groups  of 
four  or  five,  which  are  separated  by  a  fine  connective  tissue.  Two 
or  three  tubes  often  open  into  one  duct,  which  forms  about  a  third 
of  the  whole  length  of  the  tube  and  opens  on  the  surface.  The 
ducts  are  lined  with,  columnar  epithelium.  Of  the  gland  tube 
proper,  i.e.,  the  part  of  the  gland  below  the  duct,  the  upper  third 
is  the  neck  and  the  rest  the  body.  The  neck  is  narrower  than  the 
body,  and  is  lined  with  granular  cubical  cells  which  are  continuous 
with  the  columnar  cells  of  the  duct.  Between  these  cells  and  the 
membrana  propria  of  the  tubes,  are  large  oval  or  spherical  cells, 
opaque  or  granular  in  appearance,  with  clear  oval  nuclei,  bulging 
out  the  membrana  propria ;  these  cells  are  called  peptic  or  parietal 
cells.  They  do  not  form  a  continuous  layer.  The  body,  which 
is  broader  than  the  neck  and  terminates  in  a  blind  extremity  or 
fundus  near  the  muscularis  mucosas,  is  lined  by  cells  continuous 
with  the  cubical  or  central  cells  of  the  neck,  but  longer,  more 
columnar  and  more  transparent.  In  this  part  are  a  few  parietal 
cells  of  the  same  kind  as  in  the  neck  (fig.  177). 

Ada  the  pylorus  is  approached  the  gland  ducts  become  longer, 
and  the  tube  proper  becomes  shorter,  and  occasionally  branched 
at  the  fundus. 

(6)  Pyloric  Glands. — These  glands  (fig.  179)  have  much  longer 


3oo 


DIGESTION. 


[chap.  VIII 


ducts  than  the  peptic  glands.  Into  each  duct  two  or  three  tubes 
open  by  very  short  and  narrow  necks,  and  the  body  of  each  tube 
is  branched,   wavy,    and  convoluted.      The  lumen   is   very  large. 


' 


1 


if   m 
§  if" 


Fig.  177. — from  0  vertical  section  through  (he  mucous  membrane  of  the  cardiac  end  of  stomach. 

Two  peptic  glands  are  shown  with  a  duct  common  to  both,  one  gland  only  in  part. 
a,  duct  with  columnar  epithelium  becoming  shorter  as  the  cells  are  traced  downward  ; 
n,  neck  of  gland  tubes,  with  central  and  jjarietal  or  so-called  peptic  cells  ;  b,  fundus 
with  curved  enseal  extremity — the  parietal  cells  are  not  so  numerous  here.  X  400. 
(Klein  and  Noble  Smith.) 


The  ducts  are  lined  with  columnar  epithelium,  and  the  neck  and 
body  with  shorter  and  more  granular  cubical  cells,  which  corres- 
pond with  the  central  cells  of  the  peptic  glands.     During  secretion 


4  BAP.   \  III.] 


THE    STOMACH. 


;oi 


the  cellfl   h  come,     -    in   thi  •  and 

the  g  to  the  inner  eone  of  the  cell     As  they 


a 


C <T7? 


Fig.  178. —  Tram  through  lamer  part  of  peptic  gland*  of  a  rat.    a,  peptic  cells  ;  b, 

small  spheroidal  or  cubical  cells  ;  c,  transverse  section  of  capillaries.     vFrey.) 


approach  the  duodenum  the  pyloric 
convoluted  and  more  deeply  situated. 
ous  with   Brunners   glands    in    the 
duodenum.     (Watney.) 
Changes  in  the  gla 

>.. — The  chief  or  cubical  cells 
of  the  peptic  glands,  and  the  corre- 
sponding cells  of  the  pyloric  glands 
during  the  early  stag  a   stion, 

if  hardened  in  alcohol,  appear  swollen 
and  granular,  and  stain  readily. 
A-  a  later  stag  the  cells  become 
smaller,  but  more  granular  and  stain 
even  more  readily.  The  parietal 
cells  swell  up,  but  are  otherwu 
not  altered  during  digestion.  The 
_  onles,  however,  in  the  alcohol- 
hardened  specimen,  are  believed  not 
exist  in  the  living  cells,  but  to 
have  been  precipitated  by  the  hard- 
ening re-agent  :  for  if  examined  dur- 
ing life  they  appear  to  be  confined 
to  the  inner  zone  of  the  cells,  and 
the  outer  zone  is  free  from  grannli  s, 
whereas  during  rest  the  Cull 
_  nnlar  throughout.  These  granules 
the  substance  from  which  pepsin  is 


glands  become  larger,  more 
They  are  directlv  continu- 


K'fe 


%     = 


Section  showmg  the  pyloric 
glands,  s,  free  surface  ;  a,  ducts 
of  pyloric  gland* :  ■ .  neck  of 
game ;  m,  the  gland  alveoli ; 
van,  muscularis  mucosae.  (Klein 
and  Noble  Smith.) 


are  thought  to  be  peps:. 
forme  .  which  is 


302  DIGESTION.  [CHAP,  vm. 

during  rest  stored  chiefly  in  the  inner  zone  of  the  cells  and  dis- 
charged into  the  lumen  of  the  tube  during  secretion.      (Langley.) 

Lymphatics. — Lymphatic  vessels  surround  the  gland  tubes  to  a 
greater  or  less  extent.  Towards  the  fundus  of  the  peptic  glands 
are  found  masses  of  lymphoid  tissue,  which  may  appear  as  distinct 
follicles,  somewhat  like  the  solitary  glands  of  the  small  intestine. 

Blood-vessels. — The  blood-vessels  of  the  stomach,  which  first 
break  up  in  the  submucous  tissue,  send  branches  upward  between 


•p-      jgQ p]an  nf  ftp  blood-vessels  of  the  stomach,  as  they  would  be  seen  in  a  vertical  section. 

a  arteries  passing'  up  from  the  vessels  of  submucous  coat;  b,  capillaries  branching 
between  and  around  the  tubes  ;  c,  superficial  plexus  of  capillaries  occupying  the  ridges 
of  the  mucous  membrane  ;  d,  vein  formed  by  the  union  of  veins  which,  having  collected 
the  blood  of  the  superficial  capillary  plexus,  are  seen  passing  down  between  the  tubes. 
(Brinton.) 

the  closelv  packed  glandular  tubes,  anastomosing  around  them 
by  means  of  a  fine  capillary  network,  with  oblong  meshes.  Con- 
tinuous with  this  deeper  plexus,  or  prolonged  upwards  from  it,  so 
to  speak,  is  a  more  superficial  network  of  larger  capillaries,  which 
branch  densely  around  the  orifices  of  the  tubes,  and  form  the 
framework  on  which  are  moulded  the  small  elevated  ridges  of 
mucous  membrane  bounding  the  minute,  polygonal  pits  before 
referred  to.  From  this  superficial  network  the  veins  chiefly  take 
their  origin.  Thence  passing  down  between  the  tubes,  with  no 
very  free  connection  with  the  deeper  inter-tubular  capillary  plexus, 
they  open  finally  into  the  venous  network  in  the  submucous 
tissue. 


(map.  vin.]  DIGESTION    IX    THE    STOMACH.  303 

Ntrvet.-  The  nerves  of  the  stomach  are  derived  from  the 
pneumogastrio  and  sympathetic,  and  form  a  plexus  in  the 
submucous  and  muscular  coats,  containing  many  ganglia  (Remak, 
Meissner). 


Digestion  in  the  Stomach. 

Gastric  Juice.— The  functions  of  the  stomach  are  to  secrete 
a  digestive  fluid  (gastric  juice),  to  the  action  of  which  the  food  is 
next  subjected  after  it  has  entered  the  cavity  of  the  stomach  from 
the  oesophagus  ;  to  thoroughly  incorporate  the  fluid  with  the  fond 
by  means  of  its  muscular  movements:  and  to  absorb  such  sub- 
stances as  are  capable  of  absorption.  "While  the  stomach  contains 
no  food,  and  is  inactive,  no  gastric  fluid  is  secreted  ;  and  mucus, 
which  is  either  neutral  or  slightly  alkaline,  covers  its  surface. 
But  immediately  on  the  introduction  of  food  or  other  substance 
the  mucous  membrane,  previously  quite  pale,  becomes  slightly 
turgid  and  reddened  with  the  influx  of  a  larger  quantity  of  blood; 
the  gastric  glands  commence  secreting  actively,  and  an  acid  fluid 
is  poured  out  in  minute  drops,  which  gradually  run  together  and 
flow  down  the  walls  of  the  stomach,  or  soak  into  the  substances 
within  it. 

Chemical  Composition  of  Gastric  Juice. — The  first  accu- 
rate analysis  of  gastric  juice  was  made  by  Front  :  but  it  does  not 
appear  to  have  been  collected  in  any  large  quantity,  or  pure  and 
separate  from  food,  until  the  time  when  Beaumont  was  enabled, 
by  a  fortunate  circumstance,  to  obtain  it  from  the  stomach  of  a 
man  named  St.  Martin,  in  whom  there  existed,  as  the  result  of  a 
gunshot  wound,  an  opening  leading  directly  into  the  stomach, 
near  the  upper  extremity  of  the  great  curvature,  and  three  inches 
from  the  cardiac  orifice.  The  introduction  of  any  mechanical 
irritant,  snch  as  the  bulb  of  a  thermometer,  into  the  stomach, 
excited  at  once  the  secretion  of  gastric  fluid.  This  was  drawn  off, 
and  was  often  obtained  to  the  extent  of  nearly  an  ounce.  The 
introduction  of  alimentary  substances  caused  a  much  more  rapid 
and  abundant  secretion  than  did  other  mechanical  irritants.  Xo 
increase  of  temperature  could  be  detected  during  the  most  active 
secretion  :  the  thermometer  introduced  into  the  stomach  always 
stood  at  100'  F.  (37 'S°  C.)  except  during  muscular  exertion,  when 


3C>4  DIGESTION.  [chap.  vm. 

the  temperature  of  the  stomach,  like  that  of  other  parts  of  the 
body,  rose  one  or  two  degrees  higher. 

The  chemical  composition  of  human  gastric  juice  has  been  also 
investigated  by  Schmidt.  The  fluid  in  this  case  was  obtained  by 
means  of  an  accidental  gastric  fistula,  which  existed  for  several 
years  below  the  left  mammary  region  of  a  patient  between 
the  cartilages  of  the  ninth  and  tenth  ribs.  The  mucous 
membrane  was  excited  to  action  by  the  introduction  of  some  hard 
matter,  such  as  dry  peas,  and  the  secretion  was  removed  by  means 
of  an  elastic  tube.  The  fluid  thus  obtained  was  found  to  be  acid, 
limpid,  odourless,  with  a  mawkish  taste — with  a  specific  gravity 
of  1 002,  or  a  little  more.  It  contained  a  few  cells,  seen  with  the 
microscope,  and  some  fine  granular  matter.  The  analysis  of  the 
fluid  obtained  in  this  is  given  below.  The  gastric  juice  of  dogs 
and  other  animals  obtained  by  the  introduction  into  the  stomach 
of  a  clean  sponge  through  an  artificially  made  gastric  fistula, 
shows  a  decided  difference  in  composition,  but  possibly  this  is 
due,  at  least  in  part,  to  admixture  with  food. 

Chemical  Composition  of  Gastric  Juice. 


Dog's. 

Human, 

Water 

971-17 

994*4 

Solids 

28-82 

539 

Solids — 

Ferment — Pepsin          ..... 

175 

319 

Hydrochloric  acid  (free) 

27 

•2 

Salts- 

Calcium,  sodium,  and  potassium,  chlorides  ; 

and  calcium,  magnesium,  and  iron,  phos- 

phates       ....... 

S-57 

2-19 

The  quantity  of  gastric  juice  secreted  daily  has  been  variously 
estimated ;  but  the  average  for  a  healthy  adult  may  be  assumed 
to  range  from  ten  to  twenty  pints  in  the  twenty-four  hours. 
The  acidity  of  the  fluid  is  due  to  free  hydrochloric  acid,  although 
other  acids,  e.g.,  lactic,  acetic,  butyric,  are  not  unfrequently  to  be 
found  therein  as  products  of  gastric  digestion.  The  amount  of 
hydrochloric  acid  varies  from  2  to  '2  per  1000  parts.  In  health}' 
gastric  juice  the  amount  of  free  acid  may  be  as  much  as  '2  per  cent. 


ohap,  nil.]  GA8TBIC    JTJI<  305 

Aj  regards  the  formatioD  of  pepsin  and  acid,  the  formi 
produced  by  the  central  or  chief  cells  of  the  peptic  glands,  and 
also  most  likely  by  the  similar  cells  in  the  pyloric  glands;  the 
acid  is  chiefly  found  at  the  surface  of  the  mucous  membrane,  but 
is  in  all  probability  formed  by  the  secreting  action  of  the  parietal 
cells  of  the  peptic  glands,  ;i-  no  acid  is  formed  by  the  pyloric 
glands  in  which  this  variety  of  cell  is  absent. 

The  ferment  Pepsin  (p.  305)  can  be  procured  by  digesting'  por- 
tions of  the  mucous  membrane  of  the  stomach  in  cold  water,  after 
they  have  been  macerated  for  some  time  in  water  at  a  temperature 
8o° — ioo:  I".  2y° — 37*8°  C).  The  warm  water  dissolves  various 
substances  as  well  ;ts  some  of  the  pepsin,  but  the  cold  water  takes 
up  little  else  than  pepsin,  which  is  contained  in  a  greyish-brown 
viscid  fluid,  on  evaporating  the  cold  solution.  The  addition  of 
alcohol  throws  down  the  pepsin  in  greyish-white  floccnli.  Glycerine 
also  has  the  property  of  dissolving  out  the  ferment  ;  and  if  the 
mucous  membrane  be  finely  minced  and  the  moisture  removed  by 
absolute  alcohol,  a  powerful  extract  may  be  obtained  by  throwing 
into  glycerine. 

Functions. — The  digestive  power  of  the  gastric  juice  depends 
on  the  pepsin  and  acid  contained  in  it,  both  of  which  are,  under 
ordinary  circumstances,  necessary  for  the  process. 

The  general  effect  of  digestion  in  the  stomach  is  the  conversion 
of  the  food  into  chyme,  a  substance  of  various  composition  accord- 
ing to  the  nature  of  the  food,  yet  always  presenting  a  character- 
istic thick,  pultaceous,  grumous  consistence,  with  the  undigested 
portions  of  the  food  mixed  in  a  more  fluid  substance,  and  a  strong, 
disagreeable  acid  odour  and  taste. 

The  chief  function  of  the  gastric  juice  is  to  convert  proi 
into  peptones.  This  action  may  be  shown  by  adding  a  little 
gastric  juice  (natural  or  artificial)  to  some  diluted  egg-albumin, 
and  keeping  the  mixture  at  a  temperature  of  about  100'  F. 
(37*8°  C.) ;  it  is  soon  found  that  the  albumin  cannot  be  preci- 
pitated on  boiling,  but  that  if  the  solution  be  neutralised  with  an 
alkali,  a  precipitate  of  acid-albumin  is  thrown  down.  After  a  while 
the  proportion  of  acid-albumin  gradually  dimin  that  at  last 

scarcely  any  precipitate  results  on  neutralization,  and  finally  it  is 
found  that  all  the  albumin  has  been  changed  into  another  proteid 


306  DIGESTION.  [chap.  vm. 

substance  which  is  not  precipitated  on  boiling  or  on  neutraliza- 
tion.    This  is  called  peptone. 

Characteristics  of  Peptones. — Peptones  have  certain  characteristics 
which  distinguish  them  from  other  proteids.  i.  They  are  diffu- 
sible, i.e.,  they  possess  the  property  of  passing  through  animal 
membranes.  2.  They  cannot  be  precipitated  by  heat,  nitric,  or 
acetic  acid,  or  potassium  ferrocyanide  and  acetic  acid.  They  are, 
however,  thrown  down  by  tannic  acid,  by  mercuric  chloride  and 
by  picric  acid.  3.  They  are  very  soluble  in  water  and  in  neutral 
saline  solutions. 

In  their  diftusibility  peptones  differ  remarkably  from  egg- 
albumin,  and  on  this  diftusibility  depends  one  of  their  chief  uses. 
Egg-albumin  as  such,  even  in  a  state  of  solution,  would  be  of 
little  service  as  food,  inasmuch  as  its  indiffusibility  would  effec- 
tually prevent  its  passing  by  absorption  into  the  blood-vessels  of 
the  stomach  and  intestinal  canal.  Changed,  however,  by  the 
action  of  the  gastric  juice  into  peptones,  albuminous  matters 
diffuse  readily,  and  are  thus  quickly  absorbed. 

After  entering  the  blood  the  peptones  are  very  soon  again 
modified,  so  as  to  re-assume  the  chemical  characters  of  albumin, 
a  change  as  necessary  for  preventing  their  diffusing  out  of  the 
blood-vessels,  as  the  previous  change  was  for  enabling  them  to 
pass  in.  This  is  effected,  probably,  in  great  part  by  the  agency 
of  the  liver. 

Products  of  Gastric  Digestion. — The  chief  product  of  gastric 
digestion  is  undoubtedly  peptone.  We  have  seen,  however,  in  the 
above  experiment  that  there  is  a  by-product,  and  this  is  almost 
identical  with  syntonin  or  acid  albumin.  This  body  is  probably 
not  exactly  identical,  however,  with  syntonin,  and  its  old  name  of 
parapeptone  had  better  be  retained.  The  conversion  of  native 
albumin  into  acid  albumin  may  be  effected  by  the  hydrochloric 
acid  alone,  but  the  further  action  is  undoubtedly  due  to  the 
ferment  and  the  acid  together,  as  although  under  high  pressure 
any  acid  solution  may,  it  is  said,  if  strong  enough,  produce  the 
entire  conversion  into  peptone,  under  the  condition  of  digestion 
in  the  stomach  this  would  be  quite  impossible  ;  and,  on  the  other 
hand,  pepsin  Avill  not  act  without  the  presence  of  acid.  The  pro- 
duction of  two   forms   of  peptone   is  usually  recognised,   called 


chap,  vim. 1  G  ISTRIC    DIGESTION. 


307 


respectively  anii-peptone  and  &m*-peptone.  Their  different 
chemical  properties  have  not  yet  been  made  out,  but  they  are 
distinguished  by  this  remarkable  fact,  thai  the  pancreatic  juice, 
while  possessing  no  action  over  the  former,  is  able  to  convert  the 
latter  into  leucin  and  tyrosin.  Pepsin  acts  the  pari  of  a  hydro- 
lytic  ferment  proteolytic),  and  a])pcars  to  cause  hydration  of 
albumin,  peptone  being  a  highly  hydrated  form  of  albumin. 

Circumstances  favouring  Gastric  Digestion.  1. — A  tem- 
perature of  about  ioo°  F.  (37-8°  (\);  at  320  F.  (o°  C.)  it  is 
delayed,  and  by  boiling  is  altogether  stopped.  2.  An  acid 
medium  is  necessary.  Hydrochloric  is  the  best  acid  for  the 
purpose.  Excess  of  acid  or  neutralization  stops  the  process.  3. 
The  removal  of  the  products  of  digestion.  Excess  of  peptone 
delays  the  action. 

Action  of  the  Gastric  Juice  on  Bodies  other  than  Proteids. 
— All  proteids  are  converted  by  the  gastric  juice  into  peptone-, 
and,  therefore,    whether  they  be  taken  into  the  body  in   meat, 

£8,  milk,  bread,  or  other  foods,  the  resultant  still  is  peptone. 

Milk  is  curdled,  the  casein  being  precipitated,  and  then  dissolved. 
The  curdling  is  due  to  a  special  ferment  of  the  gastric  juice 
(curdling  ferment),  and  is  not  due  to  the  action  of  the  free  acid 
only.  The  effect  of  rennet,  which  is  a  decoction  of  the  fourth 
stomach  of  a  calf  in  brine,  has  long  been  known,  as  it  is  used 
extensively  to  cause  precipitation  of  casein  in  cheese  manufacture. 

The  ferment  which  produces  this  curdling  action  is  distinct 
from  pepsin. 

Gelatin  is  dissolved  and  changed  into  peptone,  as  are  also 
chondrin  and  elastin ;  but  niacin,  and  the  horny  tissues,  keratin 
generally  are  unaffected. 

(>n  the  amylaceous  articles  of  food,  and  upon  pure  oleaginous 
principles  the  gastric  juice  has  no  action.  In  the  case  of  adipose 
tissue,  its  effect  is  to  dissolve  the  areolar  tissue,  albuminous  cell- 
walls,  etc.,  which  enter  into  its  composition,  bj  which  means  the 
fat  is  able  to  mingle  more  uniformly  with  the  other  constituents 
of  the  chynu . 

The  gastric  fluid  acts  as  a  general  solvent  for  some  of  the 
saline  constituents  of  the  food,  as,  for  example,  particles  of 
common  salt,  which  may  happen  to  have  escaped  solution  in  the 
saliva;  while  its  acid  may  enable  it  to  dissolve  some  other  salts 

x  2 


308  DIGESTION.  [cHAi-.  viir. 

which  are  insoluble  in  the  latter  or  in  water.  It  also  dissolves 
cane  sugar,  and  by  the  aid  of  its  mucus  causes  its  conversion  in 
part  into  grape  sugar. 

The  action  of  the  gastric  juice  in  preventing  and  checking 
putrefaction  has  been  often  directly  demonstrated.  Indeed,  that 
the  secretions  which  the  food  meets  with  in  the  alimentary 
canal  are  antiseptic  in  their  action,  is  what  might  be  antici- 
pated, not  only  from  the  proneness  to  decomposition  of  organic 
matters,  such  as  those  used  as  food,  especially  under  the  in- 
fluence of  warmth  and  moisture,  but  also  from  the  well-known 
fact  that  decomposing  flesh  {e.g.,  high  game)  may  be  eaten  with 
impunity,  while  it  would  certainly  cause  disease  were  it  allowed  to 
enter  the  blood  by  any  other  route  than  that  formed  by  the 
organs  of  digestion. 

Time  occupied  in  Gastric  Digestion — Under  ordinary 
conditions,  from  three  to  four  hours  may  be  taken  as  the  average 
time  occupied  by  the  digestion  of  a  meal  in  the  stomach.  But 
many  circumstances  will  modify  the  rate  of  gastric  digestion.  The 
chief  are  :  the  nature  of  the  food  taken  and  its  quantity  (the 
stomach  should  be  fairly  filled — not  distended)  ;  the  time  that  has 
elapsed  since  the  last  meal,  which  should  be  at  least  enough  for 
the  stomach  to  be  quite  clear  of  food ;  the  amount  of  exercise 
previous  and  subsequent  to  a  meal  (gentle  exercise  being  favour- 
able, over-exertion  injurious  to  digestion) ;  the  state  of  mind 
(tranquillity  of  temper  being  essential,  in  most  cases,  to  a  quick 
and  due  digestion) ;  the  bodily  health  ;  and  some  others. 

Movements  of  the  Stomach. — The  gastric  fluid  is  assisted 
in  accomplishing  its  share  in  digestion  by  the  movements  of  the 
stomach.  In  granivorous  birds,  for  example,  the  contraction  of 
the  strong  muscular  gizzard  affords  a  necessary  aid  to  digestion, 
by  grinding  and  triturating  the  hard  seeds  which  constitute  part 
of  the  food.  But  in  the  stomachs  of  man  and  other  Mammalia 
the  motions  of  the  muscular  coat  are  too  feeble  to  exercise  any 
such  mechanical  force  on  the  food  ;  neither  are  they  needed,  for 
mastication  has  already  done  the  mechanical  work  of  a  gizzard ; 
and  experiments  have  demonstrated  that  substances  enclosed 
in  perforated  tubes,  and  consequently  protected  from  mechanical 
influence,  are  yet  digested. 

The   normal    actions    of    the    muscular   fibres  of  the    human 


chap,  tiii.]  GA8TRIC    DIGESTION.  309 

mach  appear  to  have  a  three-fold  pui  (1)  to  adapt  the 

mach  to  the  quantity  of  food  in  it,  bo  that  its  walls  may  be  in 
contact  with  the  food  on  all  Bides,  and,  at  the  same  time,  may 

•  a  certain  amount  of  compression   upon   it:  (2)  to  k- • 
the  orifices  of  the  stomach  closed  until  the  food  is  digested  ;  and 

to  perform  certain  peristaltic  movements,  whereby  the  food, 

it    becomes  chymified,   is   gradually   propelled   towards,    and 
ultimately  through,   the  pylorus.     In  accomplishing  this  latter 
end,  the  movements  without  doubt  materially  contribute  towai 
effecting  a  thorough  intermingling  of  the  food  and  the  gastric  fluid. 

When  digestion  is  not  going  on,  the  stomach  is  uniformly 
contracted,  its  orifices  not  more  firmly  than  the  rest  of  its  walls  ; 
but.  if  examined  Bhortly  after  the  introduction  of  food,  it  is 
found  closely  encircling  its  contents,  and  its  orifices  are  firmly 
closed  like  sphincters.      The  cardiac  orifice,   every  time  food  is 

illowed,  opens  to  admit  its  passage  to  the  stomach,  and  imme- 
diately again  closes.  The  pyloric  orifice,  during  the  first  pan  of 
_  -trie  digestion,  is  usually  so  completely  closed,  that  even  when 
the  stomach  is  separated  from  the  intestines,  none  of  its  contents 

ape.  But  towards  the  termination  of  the  digestive  process,  the 
pylorus  seems  to  offer  less  r  sistance  to  the  passage  of  substances 
from  the  stomach;  first  it  yields  to  allow  the  successively  digested 
portions  to  go  through  it;  and  then  it  allows  the  transit  of  even 
undigested  substances.  It  appears  that  food,  so  soon  as  it  enters 
the  stomach,  is  subjected  to  a  kind  of  peristaltic  action  of  the 
muscular  coat,  whereby  the  digested  portions  are  gradually  moved 
towards  the  pylorus.  The  movements  were  observed  to  increase 
in  rapidity  as  the  process  of  chymification  advanced,  and  were 
continued  until  it  was  completed. 

The  contraction  of  the  fibres  situated  towards  the  pyloric  end 
of  the  stomach  seems  to  be  more  energetic  and  more  decidedly 

ristaltic  than  those  of  the  cardiac  portion.  Thus,  it  was  found 
in  the  case  of  St.  Martin,  that  when  the  bulb  of  the  thermo- 
meter was  placed  about  three  inches  from  the  pylorus,  through 
the  gastric  fistula,  it  was  tightly  embraced  from  time  to  time,  and 
drawn  towards  the  pyloric  orifice  for  a  distance  of  three  or 
four  inches.  The  object  of  this  movement  appeal's  to  be. 
just  said,  to  carry  the  food  towards  the  pylorus  as  fast  as  it 
formed    into    chyme,    and    to   propel    the    chyme    into    the 


310  DIGESTION.  [chap.  vnr. 

duodenum  ;  the  undigested  portions  of  food  being  kept  back 
until  they  are  also  reduced  into  chyme,  or  until  all  that  is 
digestible  has  passed  out.  The  action  of  these  fibres  is  often 
seen  in  the  contracted  state  of  the  pyloric  portion  of  the 
stomach  after  death,  when  it  alone  is  contracted  and  firm,  while 
the  cardiac  portion  forms  a  dilated  sac.  Sometimes,  by  a  pre- 
dominant action  of  strong  circular  fibres  placed  between  the  cardia 
and  pylorus,  the  two  portions,  or  ends  as  they  are  called,  of  the 
stomach,  are  partially  separated  from  each  other  by  a  kind  of  hour- 
glass contraction.  By  means  of  the  peristaltic  action  of  the  mus- 
cular coats  of  the  stomach,  not  merely  is  chymified  food  gradually 
propelled  through  the  pylorus,  but  a  kind  of  double  current  is 
continually  kept  up  among  the  contents  of  the  stomach,  the 
circumierential  parts  of  the  mass  being  gradually  moved  onward 
towards  the  pylorus  by  the  contraction  of  the  muscular  fibres, 
while  the  central  portions  are  propelled  in  the  opposite  direction, 
namely,  towards  the  cardiac  orifice  :  in  this  way  is  kept  up  a 
constant  circulation  of  the  contents  of  the  viscus,  highly  con- 
ducive to  their  free  mixture  with  the  gastric  fluid  and  to  their 
ready  digestion. 

Vomiting. — The  expulsion  of  the  contents  of  the  stomach  in 
vomitingr,  like  that  of  mucous  or  other  matter  from  the  lungs  in 
coughing,  is  preceded  by  an  inspiration ;  the  glottis  is  then  closed, 
and  immediately  afterwards  the  abdominal  muscles  strongly  act ; 
but  here  occurs  the  difference  in  the  two  actions.  Instead  of  the 
vocal  cords  yielding  to  the  action  of  the  abdominal  muscles,  they 
remain  tightly  closed.  Thus  the  diaphragm  being  unable  to  go 
up,  forms  an  unyielding  surface  against  which  the  stomach  can  be 
pressed.  In  this  way,  as  well  as  by  its  own  contraction,  it 
is  fixed,  to  use  a  technical  phrase.  At  the  same  time  the 
cardiac  sphincter-muscle  being  relaxed,  and  the  orifice  which 
it  naturally  guards  being  actively  dilated,  while  the  pylorus  is 
closed,  and  the  stomach  itself  also  contracting,  the  action  of  the 
abdominal  muscles,  by  these  means  assisted,  expels  the  contents 
of  the  organ  through  the  oesophagus,  pharynx,  and  mouth.  The 
reversed  peristaltic  action  of  the  oesophagus  probably  inert 
the  effect. 

It  has  been  frequently  stated  that  the  stomach  itself  is  quite 
passive  during  vomiting,  and  that  the  expulsion  of  its  contents  is 


i  bap.  vim.]  VOMITING.  3!  i 

effected  solely  by  the  pi  upon  it  when  the  • 

of  the  abdomen  is  diminished  bythe  contraction  of  the  diaphragm, 

and  subsequently  of  the  abdominal  muscles.     The  experirj 

an<l  observations,    however,  which  an  to  confirm  this 

s  iow   that   ti.  tion   of   the   abdominal 

:les  alone  is  sufficient  to  expel   matters  from  an  am 

_  _      •  -         _      .    and   that,  under   very   abnormal 

circumstances,  the  si  i,   by  itself,  cannot  expel  its  i 

They  by  no  mes     -         w  that  in  ordinary  vomiting  the 

nd,  "ii   the  other  hand,  there   arc    g  -    :   I 

believing  the  contrary. 

It  is  true  that  facts  are  wanting  to  demonstrate  with  certainty 

iction  of  the  stomach  in  vomiting;  but  - 

fistul  ning  into  the  organ  appear  to  support  the  belief  that 

a   take  ['lace  ;  and  the  analogy  of  the  case  of  the  stomach 

with  that  of  the  other  hollow  viscera,  as  the  rectum  and  bladder, 

may  be  also  cited  in  confirmation. 

The  ncerned  in  the  act  of  vomiting,  are  chiefly  and 

primarily   those    of    the    abdomen;     the    diaphragm     ale 
but  usually  not  as  the  muscles  of  the  abdominal  walls  do. 
contract  and  compress  the  atom    ;h  more  and  more  towards  the 
diaphragm ;  and  the  diaphragm  (which  is  usually  drawn  down  in 
the  deep  inspiration  that  precedes  each  act  of  vomiting)  is  fixed, 
and  presents  an  unyielding   surface  against   which  the   stomach 
maybe  pressed.     The  diaphragm  is,  therefore,  as  a  rule  pa- 
during  the  actual  expulsion  of  the  contents  of  the  stomach.     But 
there  are  grounds  for  believing  that  sometimes  this  muscle  actively 
contracts,  so  that  the  stomach  is,  so  to  5]  -  jiieezed  bet 

the     descending     diaphragm     and     the     retracting     abdominal 
walls. 

S  me  per>  ssess   the   power  of  vomiting  at  will,  without 

applying  any  undue  irritation  to  the  stomach,  but  simply 
voluntary  effort.  It  seems  also,  that  tins  power  may  be  acquired 
by  those  who  do  not  naturally  possess  it,  and  by  continual  prac- 
tice may  become  a  habit.  There  are  i  -  i  of  rare  occurrence 
in  which  persons  habitually  swallow  their  food  hastily,  and  nearly 
nnmasticated,  and  then  at  their  leisure  i  _  _.:ate  it,  piece  by 
piece,  into  their  mouth,  remasticate,  and  again  swallow  it,  like 
members  of  the  ruminant  order  of  Mammalia. 


312  DIGESTION.  [chap.  viii. 

The  various  nerve-actions  concerned  in  vomiting  are  governed 
by  a  nerve-centre  situate  in  the  medulla  oblongata. 

The  sensory  nerves  are  the  fifth,  glossopharyngeal  and  vagus 
principally  ;  but,  as  well,  vomiting  may  occur  from  stimulation  of 
sensory  nerves  from  many  organs,  e.g.,  kidney,  testicle,  kc.  The 
centre  may  also  be  stimulated  by  impressions  from  the  cerebrum 
and  cerebellum,  so  called  central  vomiting  occurring  in  disease  of 
those  parts.  The  efferent  impulses  are  carried  by  the  phrenics 
and  the  spinal  nerves. 

Influence  of  the  Nervous  System  on  Gastric  Digestion. 
— The  normal  movements  of  the  stomach  during  gastric  digestion 

CO  o 

are  directly  connected  with  the  plexus  of  nerves  and  ganglia  con- 
tained in  its  walls,  the  presence  of  food  acting  as  a  stimulus  which 
is  conveyed  to  the  ganglia  and  reflected  to  the  muscular  fibres. 
The  stomach  is,  however,  also  directly  connected  with  the  higher 
nerve-centres  by  means  of  branches  of  the  vagus  and  solar  plexus 
of  the  sympathetic.  The  vaso-motor  fibres  of  the  latter  are  de- 
rived, probably,  from  the  splanchnic  nerves. 

The  exact  function  of  the  vagi  in  connection  with  the  move- 
ments of  the  stomach  is  not  certainly  known.  Irritation  of  the 
vagi  produces  contraction  of  the  stomach,  if  digestion  is  proceed- 
ing ;  while,  on  the  other  hand,  peristaltic  action  is  retarded  or 
stopped,  when  these  nerves  are  divided. 

Bernard,  watching  the  act  of  gastric  digestion  in  dogs  which 
had  fistulous  openings  into  their  stomachs,  saw  that  on  the 
instant  of  dividing  their  vagic  nerves,  the  process  of  diges- 
tion was  stopped,  and  the  mucous  membrane  of  the  stomach, 
previously  turgid  with  blood,  became  pale,  and  ceased  to 
secrete.  These  facts  may  be  explained  by  the  theory  that  the 
vagi  are  the  media  by  which,  during  digestion,  an  inhibitory 
impulse  is  conducted  to  the  vaso-motor  centre  in  the  medulla ; 
such  impulse  being  reflected  along  the  splanchnic  nerves  to  the 
blood-vessels  of  the  stomach,  and  causing  their  dilatation 
(Rutherford).  From  other  experiments  it  may  be  gathered,  that 
although  division  of  both  vagi  always  temporarily  suspends  the 
secretion  of  gastric  fluid,  and  so  arrests  the  process  of  digestion, 
being  occasionally  followed  by  death  from  inanition ;  yet  the 
digestive  powers  of  the  stomach  may  be  completely  restored  after 
the  operation,  and  the  formation  of  chyme  and  the  nutrition  of 


/ 


<iiAP.  vin.]  NERV0U8    INFLUENCE,  313 

the  animal  may  be  carried  on  almost  as  perfectly  as  iii  health. 
This  would  indicate  the  existence  of  a  special  local  nervous 
mechanism  which  controls  the  Becretion. 

Bernard  found  that  galvanic  Btimulus  <>f  these  nerves  excited 

an  active  secretion  of  the  fluid,  while  a  like  stimulus  applied  to 
the  sympathetic  nerves  issuing  from  the  semilunar  ganglia,  caused 
a  diminution  and  even  complete  arrest  of  the  secretion. 

The  influence  of  the  higher  nerve-centres  on  gastric  digestion, 
as  in  the  case  of  mental  emotion,  is  too  well  known  to  need  more 
than  a  reference. 

Digestion  of  the  Stomach  after  Death. — If  an  animal  die 
during  the  process  of  gastric  digestion,  and  when,  therefore,  a 
quantity  of  gastric  juice  is  present  in  the  interior  of  the  stomach, 
the  walls  of  this  organ  itself  are  frequently  themselves  acted  on  by 
their  own  secretion,  and  to  such  an  extent,  that  a  perforation  of 
considerable  size  maybe  produced,  and  the  contents  of  the  stomach 
may  in  part  escape  into  the  cavity  of  the  abdomen.  This  pheno- 
menon is  not  unfrequently  observed  in  post-mortem  examinations  of 
the  human  body.  If  a  rabbit  be  killed  during  a  period  of  digestion, 
and  afterwards  exposed  to  artificial  warmth  to  prevent  its  tempe- 
rature from  falling,  not  only  the  stomach,  but  many  of  the  sur- 
rounding parts  will  be  found  to  have  been  dissolved  (Pavy). 

From  these  facts,  it  becomes  an  interesting  question  why,  during 
life,  the  stomach  is  free  from  liability  to  injury  from  a  secretion, 
which,  after  death,  is  capable  of  such  destructive  effects  1 

It  is  only  necessary  to  refer  to  the  idea  of  Bernard,  that  the 
living  stomach  finds  protection  from  its  secretion  in  the  presence 
of  epithelium  and  mucus,  which  are  constantly  renewed  in  the 
same  degree  that  they  arc  constantly  dissolved,  in  order  to  remark 
that  although  the  gastric  mucus  is  probably  protective,  this  theory, 
so  far  as  the  epithelium  is  concerned,  has  been  disproved  by  expe- 
riments of  Pavy's,  in  which  the  mucous  membrane  of  the  stomachs 
of  dogs  was  dissected  off  for  a  small  space,  and,  on  killing  the 
animals  some  days  afterwards,  no  sign  of  digestion  of  the  stomach 
was  visible.  "  Upon  one  occasion,  after  removing  the  mucous 
membrane,  and  exposing  the  muscular  fibres  over  a  space  of  about 
an  inch  and  a  half  in  diameter,  the  animal  was  allowed  to  live  for 
ten  days.  It  ate  food  every  day,  and  seemed  scarcely  affected  by 
the  operation.     Life   was  destroyed  whilst   digestion  was    being 


314 


DIGESTION. 


[chap.  viii. 


carried  on,  and  the  lesion  in  the  stomach  was  found  very  nearly 
repaired  :  new  matter  had  been  deposited  in  the  place  of  what 
had  been  removed,  and  the  denuded  spot  had  contracted  to  much 
less  than  its  original  dimensions." 

Pavy  believes  that  the  natural  alkalinity  of  the  blood,  which 
circulates  so  freely  during  life  in  the  walls  of  the  stomach,  is 
sufficient  to  neutralize  the  acidity  of  the  gastric  juice;  and  as  may 


Fig.  181. — Auerbach's  nerve-plexus  in  small  intestine.  The  plexus  consists  of  fibrillated 
substance,  and  is  made  up  of  trabecular  of  various  thicknesses.  Nucleus-like  elements 
and  ganglion-cells  are  imbedded  in  the  plexus,  the  whole  of  which  is  enclosed  in  a 
nucleated  sheath.    (Klein.) 

be  gathered  from  what  has  been  previously  said,  the  neutralization 
of  the  acidity  of  the  gastric  secretion  is  quite  sufficient  to  destroy 
its  digestive  powers ;  but  the  experiments  adduced  in  favour  of  this 
theory  are  open  to  many  objections,  and  afford  only  a  negative  support 
to  the  conclusions  they  are  intended  to  prove.  Again,  the  pancreatic 
secretion  acts  best  on  proteids  in  an  alkaline  medium ;  but  it  has 
no  digestive  action  on  the  living  intestine.  It  must  be  confessed 
that  no  entirely  satisfactory  theory  has  been  yet  stated. 


The   Intestines. 

The  Intestinal  Canal  is  divided  into  two  chief  portions,  named 
from  their  differences  in  diameter,  the   (I.)  small  and  (II.)  large 


CHAP.  VIII.] 


THE    INTESTINES. 


315 


intestine  (fig.  165).  These  are  continuous  with  each  other,  and 
communicate  by  means  of  an  opening  guarded  by  a  valve,  the 
Ueo-ccecal  valve,  which  allows  the  passage  of  the  products  of 
digestion  tV.au  the  -mall  into  the  large  bowel,  but  not,  under 
ordinary  circumstances,  in  the  opposite  direction. 

/.  Th  Small  I  at- sin'. — The  Small  Intestine,  the  average  Length 
of  which  in  an  adult  is  about  twenty  feet,  has  been  divided,  for 
convenience  of  description,  into  three  portions,  viz.,  the  duodenum^ 
which  extends  for  eight  or  ten  inches  beyond  the  pylorus;  the 
jejunum,  which  forms  two-fifths,  and  the  thum,  which  forms  three- 
tifths  of  the  rest  of  the  canal. 

Structure. — The  small  intestine,  like  the  stomach,  is  con- 
structed of  f«.ur  principal  coats,  viz.,  the  serous,  muscular,  sub- 
mucous, and  mucous. 

(1.)  The  serous  coat,  formed  by  the  visceral  layer  of  the  peri- 
toneum, and  has  the  structure  of  serous  membranes  in  general. 

(2.)  The  muscular  coats  consist  of  an  internal  circular  and 
an  external  longitudinal  layer  :   the  former  is  usually  considerably 


Fig.  182. — Horizontal  section  of  a  si  tall  fragment  of  the  mucous  nt«m&raii0,  including  one  entire 
crypt  of  Lieberkiihn  and  parts  of  several  others  :  a,  cavity  of  the  tubular  glands  or 
crypts  :  b,  one  of  the  lining  epithelial  cells ;  r,  the  lymphoid  or  retiform  spaces,  of 
■which  some  are  empty,  and  others  occupied  by  lymph  cells,  as  at  (/. 


the  thicker.  Both  alike  consist  of  bundles  of  unstriped  muscular 
tissue  supported  by  connective  tissue.  They  are  well  provided 
with  lymphatic  vessels,  which  form  a  set  distinct  from  those  of  the 
mucous  membrane. 

Between  the  two  muscular  coats  is  a  nerve-plexus  (Auerbach's 


3i6 


DIGESTION. 


[(HAT.  VIII. 


plexus,  plexos  myentericus)  (fig.  181)  similar  in  structure  to 
Meissner's  (in  the  submucous  tissue),  but  with  more  numerous 
ganglia.  This  plexus  regulates  the  peristaltic  movements  of  the 
muscular  coats  of  the  intestines. 

(3.)  Between  the  mucous  and  muscular  coats,  is  the  submucous 
coat,  which  consists  of  connective  tissue,  in  which  numerous  blood- 
vessels and  lymphatics  ramify.  A  fine  plexus,  consisting  mainly 
of  non-medullated  nerve-fibres,  "  Meissner's  plexus,"  with  ganglion 

cells  at  its  nodes,  occurs  in 
the  submucous  tissue  from  the 
stomach  to  the  anus.  From 
the  position  of  this  plexus 
and  the  distribution  of  its 
branches,  it  seems  highly  pro- 
bable that  it  is  the  local 
centre  for  regulating  the 
calibre  of  the  blood  -  vessels 
supplying  the  intestinal 
mucous  membrane,  and  pre- 
siding over  the  processes  of 
secretion  and  absorption. 

(4.)  The  mucous  membrane 
is  the  most  important  coat 
in  relation  to  the  function  of 
digestion.  The  following 
structures,  which  enter  into 
its  composition,  may  now 
be  successively  described  ; — 
the  valvulo?  connive ntes ;  the 
villi;  and  the  glands. 
general  structure  of 
mucous  membrane  of 
intestines  resembles  that  of 
the  stomach  (p.  298),  and,  like 
it,  is  lined  on  its  inner  surface 
by  columnar  epithelium.  Adenoid  tissue  (fig.  182,  c  and  d)  enters 
largely  into  its  construction  ;  and  on  its  deep  surface  is  the  mus- 
cularis  mucosas  (m  m,  fig.  183),  the  fibres  of  which  are  arranged 
in  two  layers  :  the  outer  longitudinal  and  the  inner  circular. 


Fig.  183. — Vertical  section  through  portion  of 
small  intestine  of  dog.  v,  two  villi  showing 
e ,  epithelium  ;  g,  goblet  cells.  The  free 
surface  is  seen  to  be  formed  by  the 
"striated  basilar  border,"  while  inside 
the  villus  the  adenoid  tissue  and  un- 
striped  muscle  -  cells  are  seen ;  If, 
Lieberkuhn's  follicles  ;  m  m,  muscularis 
mucosae,  sending  up  fibres  between  the 
follicles  into  the  villi ;  rnn,  submucous 
tissue;  containing  [gm),  ganglion  cells 
of  Meissner's  plexus.     (Schofield.) 


The 
the 
the 


(II  LP.  VIII.  | 


(.LANDS    OF    SMALL    LYI'LSTI  \  L. 


317 


Valvulse  Connivontes. — The  valvulce  conniventes  (fig,  184) 
commence  in  the  duodenum,  about  one  or  two  inches  beyond  the 
pvlonis,  and  becoming  larger  and  more  numerous  immediately 
beyond  the  entrance  of  the  bile  duct,  continue  thickly  arranged 
and  well  developed  throughout  the  jejunum  ;  then,  gradually 
diminishing  in  size  and  number,  they  cease  near  the  middle  of  the 
ileum.  They  are  formed  by  a  doubling 
inwards  of  the  mucous  membrane  j  the 
crescentic,  nearly  circular,  folds  thus  formed 
being  arranged  transversely  to  the  axis  of 
the  intestine,  and  each  individual  fold  seldom 
extending  around  more  than  |  or  §  of  the 
bowel's  circumference.  Unlike  the  rugse  in 
the  oesophagus  and  stomach,  they  do  not 
disappear  on  distension  of  the  canal.  Only 
an  imperfect  notion  of  their  natural  position 
and  function  can  be  obtained  by  looking  at 
them  after  the  intestine  has  been  laid  open 
in  the  usual  manner.  To  understand  them 
aright,  a  piece  of  gut  should  be  distended 
either  with  air  or  alcohol,  and  not  opened 
until  the  tissues  have  become  hardened. 
On  then  making  a  section  it  will  be  seen 
that,  instead  of  disappearing,  they  stand 
out  at  right  angles  to  the  general  surface 

of  the  mucous  membrane  (tig.  184).  Their  functions  are  probably 
less — Besides  (1)  offering  a  largely  increased  surface  for  secretion 
and  absorption,  they  probably  (2)  prevent  the  too  rapid  passage 
of  the  very  liquid  products  of  gastric  digestion,  immediately  after 
their  escape  from  the  stomach,  and  (3),  by  their  projection,  and 
consequent  interference  with  an  uniform  and  untroubled  current 
of  the  intestinal  contents,  probably  assist  in  the  more  perfect 
mingling  of  the  latter  with  the  secretions  poured  out  to  act 
on  them. 

Glands  of  the  Small  Intestine.— The  glands  are  of  three 
principal  kinds  :— viz.,  those  of  (1)  Lieberkuhn,  (2)  Brunner,  and 
(3)  Peyer. 

(1.)  The  (/lands  or  crypts  of  Lieberlciihi  are  simple  tubular  de- 
pressions of  the  intestinal  mucous  membrane,  thickly  distributed 


Fig.  184. — Piece  ofsmn/l  in- 
testine [previously  di$- 
tended  "/»/  hardened  by 
alcohol)  laid  open  to 
show  the  normal  posi- 
tion of  the  valvule  con- 
niventes. 


3i8 


DIGESTION. 


[chap.  VIII. 


Fig.  185. — Tranverse  section  through  four 
crypts  of  Lieberkuhn  from  the  large 
intestine  of  the  pig.  They  are  lined 
by  columnar  epithelial  cells,  the 
nuclei  being  placed  in  the  outer  part 
of  the  cells.  The  divisions  between 
the  cells  are  seen  as  lines  radiating 
from  L,  the  lumen  of  the  crypt; 
G,  epithelial  cells,  which  have  become 
transformed  into  goblet  cells.  X  350. 
(Klein  and  Noble  Smith.) 


over  the  whole  surface  both  of  the  large  and  small  intestines.     In 
the  small  intestine  they  are  visible  only  with  the  aid  of  a  lens ; 

and  their  orifices   appear  as  mi- 
nute dots  scattered  between  the 
villi.    They  are  larger  in  the  large 
intestine,  and  increase  in  size  the 
nearer    they    approach   the    anal 
end   of  the   intestinal  tube ;  and 
in  the  rectum  their  orifices  may 
be  visible  to  the  naked  eye.     In 
length  they  vary  from  ^  to  ^  of 
a  line.     Each  tubule  (fig.  186)  is 
constructed  of  the  same  essential 
parts    as    the    intestinal   mucous 
membrane,  viz.,  a  fine  membrana 
propria^  or  basement  membrane, 
a  layer  of  cylindrical  epithelium 
lining    it,    and     capillary    blood- 
vessels covering  its  exterior,  the 
free  surface  of  the  columnar  cells 
presenting  an  appearance  precisely  similar  to  the  "  striated  basilar 
border"  which  covers  the  villi.     Their  contents 
appear  to  vary,   even  in  health;    the  varieties 
being   dependent,    probably,   on    the    period   of 
time  in  relation  to  digestion  at  which  they  are 
examined. 

Among   the   columnar  cells  of  Lieberkiihn's 
follicles,  goblet-cells  frequently  occur  (fig.  185). 
(2.)  Brumier's  glands   (fig.  188)   are  confined 
to  the  duodenum  ;  they  are  most  abundant  and 
thickly  set  at  the  commencement  of  this  portion 
of  the   intestine,   diminishing  gradually  as  the 
duodenum  advances.    They  are  situated  beneath 
the  mucous  membrane,  and  imbedded   in   the 
submucous  tissue,  each  gland  is  a  branched  and 
convoluted  tube,  lined  with  columnar  epithelium. 
As  before  said  in  structure  they  are  very  similar 
to  the  pyloric  glands  of  the  stomach,  and  their  epithelium  under- 
goes   a   similar   change   during    secretion;    but    they    are   more 


Fig.  186. — A  gfand  of 
Lieberkilhn  in  lon- 
gitudinal section. 
(Brinton.) 


«  BAP.  VIII.] 


SMALL    INTESTIXK. 


319 


branched  and  convoluted  and  their  ducts  are  longer.  (Watney.) 
The  duct  of  each  gland  passes  through  the  muscularis  mucosa, 
ami  opens  on  the  surface  of  the  mucous  membrane. 


Fig.  187. —  T  of  injected  Peya's  glands  'from  Kolliker).    The  dra-n-ing"was 

taken  from  a  preparation  made  by  Frey  :  it  represents  the  fine  capillary-looped  net- 
work spreading  from  the  suiToundin?  blood-vessels  into  the  interior  of  three  of  Fever's 
si  iles  from  the  intestine  of  the  rabbit . 

(3.)  The  [/lands  of  Peyer  occur  chiefly  but  not  exclusively  in  the 
imall  intestine.  They  are  found  in  greatest  abundance  in  the 
lower  part  of  the  ileum  near  to  the  ileo-c?ecal  valve.  They  are 
met  with  in  two  conditions,  viz.,  either  scattered  singly,  in  which 
case  they  are  termed  <//</. nduke  solitarice,  or  aggregated  in  groups 
varying  from  one  to  three  inches  in  length  and  about  half-an-inch 
in  width,  chiefly  of  an  oval  form,  their  long  axis  parallel  with  that 
of  the  intestine.  In  this  state,  they  are  named  glandvla  agmi- 
/"it"-,  the  groups  being  commonly  called  Peyer 's  patches  (tig.  189), 
and  almost  always  placed  opposite  the  attachment  of  the  mesen- 
tery. In  structure,  and  in  function,  there  is  no  essential  difference 
between  the  solitary  glands  and  the  individual  bodies  of  which 
each  group  or  patch  is  made  up.  They  are  really  single  or  aggre- 
gated masses  of  adenoid  tissue  forming  lymph-follicles.  In  the 
condition  in  which  they  have  been  most  commonly  examined,  each 


320 


DIGESTION. 


[chap.  viii. 


gland  appears  as  a  circular  opaque-white  rounded  body,  from  -£± 
to  tV  inch  in  diameter,  according  to  the  decree  in  which  it  is 
developed.     They   are  principally   contained    in   the    submucous 


y$  mm 

§y  pi 


Fig.  188. — Vertical  section  of  duodenum,  showing  a,  villi ;  J,  crypts  of  Lieberkiihn,  and  rf 
Brunner's  glands  in  the  submucosa  s,  with  ducts,  d ;  muscularis  mucosa?,  m  ;  and 
circular  muscular  coat/.     (Schoneld.) 


coat,  but  sometimes  project  through  the  muscularis  mucosce  into 
the  mucous  membrane.  In  the  agminate  glands,  each  follicle 
reaches  the  free  surface  of  the  intestine,  and  is  covered  with 
columnar  epithelium.  Each  gland  is  surrounded  by  the  openings 
of  Lieberkiihns  follicles. 

The  adjacent  glands  of  a  Peyer's  patch  are  connected  together 
by  adenoid  tissue.  Sometimes  the  lymphoid  tissue  reaches  the 
free  surface,  replacing  the  epithelium,  as  is  also  the  case  with  some 
of  the  lymphoid  follicles  of  the  tonsil  (p.  291). 


uuxr.  viii.] 


VILLI. 


321 


Peyer's  glands  are  surrounded   by  lymphatic  Binuses  which  do 
not  penetrate  into  their  interior  ;  the  interior  is,  however,  travi 
by  a  very  rich  blood  capillary  plexus.     If  the  vermiform  appendix 


Fig.  189.— Agminate  follicles,  or  Peyer's patch,  in  a  state  of  distension,     x  5.     (Boehm.) 


of  a  rabbit,  which  consists  largely  of  Peyer's  glands,  be  injected  with 
blue,  by  pressing  the  point  of  a  fine  syringe  into  one  of  the  lym- 
phatic sinuses,  the  Peyer's  glands  will  appear  as  greyish  white 
spaces  surrounded  by  blue ;  if  now  the  arteries  of  the  same  be 
injected  with  red,  the  greyish  patches  will  change  to  red,  thus 
proving  that  they  are  surrounded  by  lymphatic  spaces,  but  pene- 
trated by  blood-vessels.  The  lacteals  passing  out  of  the  villi 
communicate  with  the  lymph  sinuses  round  Peyer's  glands. 

It  is  to  be  noted  that  they  are  largest  and  most  prominent  in 
children  and  }'oung  persons. 

Villi. — The  Villi  (figs.  183,  188,  190,  and  191),  are  confined 
exclusively  to  the  mucous  membrane  of  the  small  intestine.  They 
are  minute  vascular  processes,  from  a  quarter  of  a  line  to  a  line 
and  two-thirds  in  length,  covering  the  surface  of  the  mucous 
membrane,  and  giving  it  a  peculiar  velvety,  fleecy  appearance. 
Krause  estimates  them  at  fifty  to  ninety  in  number  in  a  square 
line,  at  the  upper  part  of  the  small  intestine,  and  at  forty  to 
seventy  in  the  same  area  at  the  lower  part.  They  vary  in  form 
even  in  the  same  animal,  and  differ  according  as  the  lymphatic 
vessels  they  contain  are  empty  or  full  of  chyle  ;  being  usually,  in 
the  former  case,  flat  and  pointed  at  their  summits,  in  the  latter 
cylindrical  or  cleavate. 


322 


DIGESTION. 


[chap,  viil 


Each  villus  consists  of  a  small  projection  of  mucous  membrane, 
and  its  interior  is  therefore  supported  throughout  by  fine  adenoid 


fig.  190. — Section  of  small  intestine  showing  villi.  Lieberkiihn's  glands  and  a  Peyer's  solitary 
gland,    m,  m,  muscularis  mucosa?.     v  Klein  and  Noble  Smith.) 

tissue,  which  forms  the  framework  or  stroma  in  which  the   other 
constituents  are  contained. 


Fig.  191. — Vertical  section  of  a  villus  0/  the  small  intestine  of  a  cat.  n,  striated  basilar  border 
of  the  epithelium  ;  5,  columnar  epithelium  ;  c,  goblet  cells  ;  d,  central  lymph-vessel  ; 
e ,  smooth  muscular  fibres  ;  f,  adenoid  stroma  of  the  villus  in  which  lymph  corpuscles 
lie.    (Klein.) 


The  surface  of  the  villus  is  clothed  by  columnar  epithelium, 
which  rests  on  a  fine  basement  membrane  :  while  within  this  are 
found,  reckoning  from  without  inwards,  blood-vessels,  fibres  of 
the  muscularis  'mucosa?,  and  a  single  lymphatic  or  lacteal  vessel 
rarely  looped  or  branched  (fig.  192) ;  besides  granular  matter,  fat- 
globules,  etc. 


CHAP.    VII!.]  VILLI. 


323 


The  epithelium  is  of  the  columnar  kind,  and  continuous  with 
that  Lining  the  other  parts  of  the  mucous 'membrane.  Tin?  cells 
arc  arranged  with  their  long  axis  radiating  from  the  surface  of 
the  villus  (fig.  191),  and  their  smaller  ends  resting  on  the  base- 
ment membrane.    The  free  surface  of  the  epithelial  cells  of  the 


Fig.  192.— A.   Villus  of  sheep.    B.  Villi  of  man.    (Slightly  altered  from  Teickmann.) 

villi,  like  that  of  the  cells  which  cover  the  general  surface  of  the 
mucous  membrane,  is  covered  by  a  fine  border  which  exhibits 
very  delicate  striations,  whence  it  derives  its  name,  "  striated 
basilar  border." 

Beneath  the  basement  or  limiting  membrane  there  is  a  rich 
supply  of  blood-vessels.  Two  or  more  minute  arteries  are  distri- 
buted within  each  villus  ;  and  from  their  capillaries,  which  form  a 
dense  network,  proceed  one  or  two  small  veins,  which  pass  out 
at  the  base  of  the  villus. 

y  2 


324 


DIGESTION. 


[('HAP.   VIII, 


The  layer  of  the  muscularis  mucosae  in  the  villus  forms  a  kind 
of  thin  hollow  cone  immediately  around  the  central  lacteal,  and 
is,     therefore,    situate  beneath    the    blood-vessels.     It    is    with- 


Fig.  193.— Diagram  of  lacteal  vessels  in  small  intestine,  a,  laeteals  in  villi;  p,  Peyer's 
glands;  b  and  d,  superficial  and  deep  network  of  laeteals  in  submucous  tissue; 
l,  Lieberkiihn's  glands  ;  s,  small  branch  of  lacteal  vessel  on  its  way  to  mesenteric 
gland  ;  H  and  o,  muscular  fibres  of  intestine  ;  s,  peritoneum.     (Teichmann.) 


out  doubt  instrumental  in  the  propulsion  of  chyle  along  the 
lacteal. 

The  lacteal  vessel  enters  the  base  of  each  villus,  and  passing 
up  in  the  middle  of  it,  extends  nearly  to  the  tip,  where  it  ends 
commonly  by  a  closed  and  somewhat  dilated  extremity.  In  the 
larger  villi  there  may  be  two  small  lacteal  vessels  which  end  by 
a  loop  (fig.  192),  or  the  laeteals  may  form  a  kind  of  network  in 
the  villus.  The  last  method  of  ending,  however,  is  rarely  or  never 
seen  in  the  human  subject,  although  common  in  some  of  the  lower 
animals  (a,  fig.  192). 

The  office  of  the  villi  is  the  absorption  of  chyle  and  other  liquids 


chap,  viii.]  LABGE   [NTE8TINE. 


3^5 


from  the  intestine.  The  mode  in  which  they  effect  this  will  be 
considered  in  the  Chapter  on  Absorption'. 

77".  Th>'  £<//■>/>  Intestine. — The  Large  Intestine,  which  in  an 
adult  is  from  about  4  to  6  feet  Long,  is  subdivided  for  descriptive 
purposes  into  three  portions  (fig.  165)  viz.  : — the  caecum,  a  short 
wide  pouch,  communicating  with  the  lower  end  of  the  small 
intestine  through  an  opening,  guarded  by  the  ileo-c&calvalxe ;  the 
.  continuous  with  the  caecum,  which  forms  the  principal  part 
«.f  the  large  intestine,  and  is  divided  into  an  ascending,  transverse, 
and  descending  portion  \  and  the  rectum,  which,  after  dilating  at 
its  lower  part,  again  contracts,  and  immediately  afterwards  opens 
externally  through  the  o.nv.<.  Attached  to  the  caecum  is  the  small 
appendix  verm  iform  is. 

Structure. — Like  the  small  intestine,  the  large  is  constructed 
of  four  principal  coats,  viz.,  the  serous,  muscular,  submucous,  and 
mucous.  The  serous  coat  need  not  be  here  particularly  described. 
Connected  with  it  are  the  small  processes  of  peritoneum,  contain- 
ing fat,  called  appendices  epiploicae.  The  fibres  of  the  muscular 
coat,  like  those  of  the  small  intestine,  are  arranged  in  two  layers 
— the  outer  longitudinal,  the  inner  circular.  In  the  csecum  and 
eolon,  the  longitudinal  fibres,  besides  being,  as  in  the  small 
intestine,  thinly  disposed  in  all  parts  of  the  wall  of  the  bowel, 
are  collected,  for  the  most  part,  into  three  strong  bands,  which 
being  shorter,  from  end  to  end,  than  the  other  coats  of  the 
intestine,  hold  the  canal  in  folds,  bounding  intermediate  sacculi. 
On  the  division  of  these  bands,  the  intestine  can  be  drawn  out 
to  its  full  length,  and  it  then  assumes,  of  course,  an  uniformly 
cylindrical  form.  In  the  rectum,  the  fasciculi  of  these  longitu- 
dinal bands  spread  out  and  mingle  with  the  other  longitudinal 
fibres,  forming  with  them  a  thicker  layer  of  fibres  than  exists  on 
any  other  part  of  the  intestinal  canal.  The  circular  muscular 
til-res  are  spread  over  the  whole  surface  of  the  bowel,  but  are 
somewhat  more  marked  in  the  intervals  between  the  sacculi 
Towards  the  lower  end  of  the  rectum  they  become  more  numerous, 
and  at  the  anus  they  form  a  strong  band  called  the  internal 
sphincter  muscle. 

The  mucous  membrane  of  the  large,  like  that  of  the  small 
intestine,  is  lined  throughout  by  columnar  epithelium,  but,  unlike 
it,  is  quite  smooth  and  destitute  of  villi,  and  is   not  projected  in 


326 


DIGESTION. 


[CHAP.  VIII. 


the  form  of  valvules  conniventes.  Its  general  microscopic  structure 
resembles  that  of  the  small  intestine  :  and  it  is  bounded  below  by 
the  muscularis  mucosce. 

The  general  arrangement  of  ganglia  and  nerve-fibres  in  the  large 
intestine  resembles  that  in  the  small  (p.  315). 

Glands  of  the  Large  Intestine— The  glands  with  which  the 
large  intestine  is  provided  are  of  two  kinds,  (1)  the  tubular  and 
(2)  the  lymphoid. 


jHo   IQ,  Horizontal  section  through  a  portion  of  the  mucous  membrane  of  the  large  intestine, 

°'<howin°-  Lieberkiihn's  glands  in  transverse  section,  a,  lumen  of  gland— lining  of 
columnar  cells  with  c,  goblet  cells,  b,  supporting  connective  tissue.  Highly  magnified. 
(V.  D.  Harris.) 

(1.)  The  tuhular  glands,  or  glands  of  Lieberkiihn,  resemble  those 
of  the  small  intestine,  but  are  somewhat  larger  and  more  numerous. 
They  are  also  more  uniformly  distributed. 

(2.)  Follicles  of  adenoid  or  lymphoid  tissue  are  most  numerous 
in  the  caecum  and  vermiform  appendix.  They  resemble  in  shape 
and  structure,  almost  exactly,  the  solitary  glands  of  the  small 
intestine.     Peyer's  patches  are  not  found  in  the  large  intestine. 

Ileo-csecal  Valve. — The  ileo-caecal  valve  is  situate  at  the  place 
of  junction  of  the  small  with  the  large  intestine,  and  guards 
against  any  reflex  of  the  contents  of  the  latter  into  the  ileum. 
It  is   composed    of  two    semilunar   folds    of  mucous   membrane 


chap,  viii.]  LARGE  INTESTINE.  327 

Each  fold  is  formed  by  a  doubling  inwards  of  the  mueous  mem- 
brane, and  is  strengthened  on  the  outside  by  some  of  the 
circular  muscular  fibres  of  the  intestine,  which  are  contained 
between  the  outer  surfaces  of  the  two  layers  of  which  each  fold 
is  composed.  While  the  circular  muscular  fibres,  however,  of  the 
bowel  at  the  junction  of  the  ileum  with  the  cajcum  are  contained 
between  the  outer  opposed  surfaces  of  the  folds  of  mucous  mem- 
brane which  form  the  valve,  the  longitudinal  muscular  fibres  and 
the  peritoneum  of  the  small  and  large  intestine  respectively  are 
continuous  with  each  other,  without  dipping  in  to  follow  the  circular 
fibres  and  the  mucous  membrane.  In  this  manner,  therefore, 
the  folding  inwards  of  these  two  last-named  structures  is  pre- 
served, while,  on  the  other  hand,  by  dividing  the  longitudinal 
muscular  fibres  and  the  peritoneum,  the  valve  can  be  made  to 
disappear,  just  as  the  constrictions  between  the  sacculi  of  the 
large  intestine  can  be  made  to  disappear  by  performing  a  similar 
operation.  The  inner  surface  of  the  folds  is  smooth  ;  the  mucous 
membrane  of  the  ileum  being  continuous  with  that  of  the 
caecum.  That  surface  of  each  fold  which  looks  towards  the  small 
intestine  is  covered  with  villi,  while  that  which  looks  to  the  caecum 
has  none.  When  the  caecum  is  distended,  the  margin  of  the  folds 
are  stretched,  and  thus  are  brought  into  firm  apposition  one  with 
the  other. 


Digestion  in  the  Intestines. 

After  the  food  has  been  duly  acted  upon  by  the  stomach,  such 
as  has  not  been  absorbed  passes  into  the  duodenum,  and  is  there 
subjected  to  the  action  of  the  secretions  of  the  pancreas  and  liver, 
which  enter  that  portion  of  the  small  intestine.  Before  consider- 
ing the  changes  which  the  food  undergoes  in  consequence, 
attention  should  be  directed  to  the  structure  and  secretion  of  these 
glands,  and  to  the  secretion  (succus  entericus)  which  is  poured  out 
into  the  intestines  from  the  glands  lining  them. 


328 


DIGESTION. 


[CHAI\  VIII. 


The  Pancreas,  and  its  Secretion. 

The  Pancreas  is  situated  within  the  curve  formed  by  the 
duodenum ;  and  its  main  duct  opens  into  that  part  of  the  small 
intestine,  through  a  small  opening,  or  through  a  duct  common 
to  it  and  to  the  liver,  about  two  and  a  half  inches  from  the 
pylorus. 

Structure. — In  structure  the  pancreas  bears  some  resemblance 
to  the  salivary  glands.  Its  capsule  and  septa,  as  well  as  the  blood- 
vessels and  lymphatics,  are  similarly  distributed.  It  is,  however, 
looser   and  softer,  the   lobes   and   lobules   being   less   compactly 

arranged.  The  main  duct 
divides  into  branches  (lobar 
ducts),  one  for  each  lobe,  and 
these  branches  subdivide  into 
intralobular  ducts,  and  these 
again  by  their  division  and 
branching  form  the  gland 
tissue  proper.  The  intralobular 
ducts  correspond  to  a  lobule, 
while  between  them  and  the 
secreting  tubes  or  alveoli  are 
longer  or  shorter  intermediarti 
ducts.  The  larger  ducts  pos- 
sess a  very  distinct  lumen  and 
a  membrana  propria  lined 
with  columnar  epithelium,  the 
cells  of  which  are  longitudin- 
ally striated,  but  are  shorter 
than  those  found  in  the  ducts 
of  the  salivary  glands.  In 
the  intralobular  ducts  the  epithelium  is  short  and  the  lumen  is 
smaller.  The  intermediary  ducts  opening  into  the  alveoli  possess 
a  distinct  lumen,  with  a  membrana  propria  lined  with  a  single 
layer  of  flattened  elongated  cells.  The  alveoli  are  branched  and 
convoluted  tubes,  with  a  membrana  propria  lined  with  a  single 
layer  of  columnar  cells.  They  have  no  distinct  lumen,  its  place 
being  taken  by  fusiform  or  branched  cells.  Heidenhain  has 
observed  that  the  alveolar  cells  in  the  pancreas  of  a  fasting  dog- 


Fig'.  195. — Section  of  tlie  pancreas  of  a  dog  during 
digestion,  a,  alveoli  lined  with  cells,  the 
outer  zone  of  which  is  well  stained  with 
hsematoxylin  ;  d,  intermediary  duet  lined 
with  squamous  epithelium.  X  350.  (Klein 
and  Noble  Smith.) 


.  hap.  viir.]  PANCREATIC  8ECBETI0N.  329 

consist  of  two  zones,  an  inner  or  central  zone,  which  is  finely  granu- 
lar, and  which  Btains  feebly,  and  a  Bmaller  parietal  zone  of  finely 
striated  protoplasm,  which  stains  easily.  The  nucleus  is  partly  in 
•  •no,  partly  in  the  other  zone.  During  digestion,  it  is  found  that 
the  outer  zone  increases  in  >i/e,  and  the  central  zone  dimini - 
the  cell  itself  becoming  smaller  from  the  discharge  of  the  secretion. 
At  the  end  of  digestion  the  first  condition  again  appears,  the  inner 
zone  enlarging  at  the  expense  of  the  outer.  It  appears  that  the 
granules  are  formed  by  the  protoplasm  of  the  cells,  from  material 
supplied  to  it  by  the  blood.  The  granules  are  thought  to  be  not 
the  ferment  itself,  but  material  from  which,  under  certain  condi- 
tions, the  ferments  of  the  gland  are  made,  and  therefore  called 
Zymogen, 

Pancreatic  Secretion. — The  secretion  of  the  pancreas  has 
been  obtained  for  purposes  of  experiment  from  the  lower  animals, 
especially  the  dog,  by  opening  the  abdomen  and  exposing  the  duct 
of  the  gland,  which  is  then  made  to  communicate  with  the  exterior. 
A  pancreatic  fistula  is  thus  established. 

An  extract  of  pancreas  made  from  the  gland,  which  has  been 
removed  from  an  animal  killed  during  digestion,  posa  3fi  -  the 
active  properties  of  pancreatic  secretion.  It  is  made  by  first  de- 
hydrating the  gland,  which  has  been  cut  up  into  small  pieces,  by 
keeping  it  for  some  days  in  absolute  alcohol,  and  then,  after  the 
entire  removal  of  the  alcohol,  placing  it  in   strong  glycerin.     A 

'    X  o  o 

glycerin  extract  is  thus  obtained.  It  is  a  remarkable  fact,  how- 
ever, that  the  amount  of  the  ferment  trypsin  greatly  in- 
creases if  the  gland  be  exposed  to  the  air  for  twenty-four  hours 
before  placing  in  alcohol ;  indeed,  a  glycerin  extract  made   from 

gland  immediately  upon  removal  from  the  body  often  appears 
to  contain  none  of  that  ferment.  This  seems  to  indicate  that 
the  conversion  of  zymogen  in  the  gland  into  the  ferment  only 
takes  place  during  the  act  of  secretion,  and  that  the  gland, 
although  it  always  contains  in  its  cells  the  materials  (trypsinogen) 
out  of  which  trypsin  is  formed,  yet  the  conversion  of  the  «>ne  into 
the  other  only  takes   place   by  degrees.     Dilute  acid   appears  to 

t  and  accelerate  the  conversion,  and  if  a  recent  pancreas  be 
rubbed  up  with  dilute  acid  before  dehydration,  a  glycerin  extract 
made  afterwards,  even  though  the  gland  may  have  been  only 
recently  removed  from  the  body,  is  very  active. 


330  DIGESTION.  [chap.  vm. 

Properties. — Pancreatic  juice  is  colourless,  transparent,  and 
slightly  viscid,  alkaline  in  reaction.  It  varies  in  specific  gravity 
from  ioioto  1015,  according  to  whether  it  is  obtained  from  a 
permanent  fistula — then  more  watery — or  from  a  newly-opened 
duct.  The  solids  vary  in  a  temporary  fistula  from  80  to  100  parts 
per  thousand,  and  in  a  permanent  one  from  16  to  50  per 
thousand. 

Chemical  Composition  of  the  Pancreatic  Secretion. 
From  a  permanent  fistula.    (Bernstein.) 

Water ■  .         .         .     975 

Solids — Ferments  : 

Proteids,  including  Serum — Albumin,  ) 
Casein,  Leucin  and  Tyrosin.  Fats  /      17 
and  Soaps        .         .         .         .         .  ) 
Inorganic  residue,  especially  Sodium  ~|        8 

Carbonate J  25 


1000 


Functions. — (1.)  It  converts  proteids  into  peptones,  the  interme- 
diate product  being  not  akin  to  syntonin  or  acid-albumin,  as  in 
gastric  digestion,  but  to  alkali-albumin.  Kiihne  believes  that 
the  intermediate  products,  both  in  the  peptic  and  pancreatic 
digestion  of  proteids,  are  two,  viz.,  antialbumose  and  hemialbu- 
mose,  and  that  the  peptones  formed  correspond  to  these,  viz., 
antipeptone  and  hemipeptone.  The  hemipeptone  is  capable  of 
being  converted  by  the  action  of  the  pancreatic  ferment — trypsin 
— into  leucin  and  tyrosin,  but  is  not  so  changed  by  pepsin  ; 
the  antipeptone  cannot  be  further  split  up.  The  products  of 
pancreatic  digestion  are  sometimes  further  complicated  by  the 
appearance  of  certain  fsecal  substances,  of  which  indol  and  naph- 
thilamine  are  the  most  important.   (Kiihne.) 

When  the  digestion  goes  on  for  a  long  time  the  indol  is  formed 
in  considerable  quantities,  and  emits  a  most  disagreeable  faecal 
odour,  which  was  attributed  to  putrefaction  till  Kiihne  showed  its 
true  nature.  All  the  albuminous  or  proteid  substances  which 
have  not  been  converted  into  peptone,  and  absorbed  in  the 
stomach,  and  the  partially  changed  substances,  i.e.,  the  para- 
peptones,  are  converted  into  peptone  by  the  pancreatic  juice,  and 
then  in  part  into  leucin  and  tyrosin. 


chap,  vin.]  PANCREATIC  SECRETION.  35I 

(2.)  Nitrogenous  bodies  other  than  /■  ■  1  <my  extent 

ottered.     Mucin   can,  however,   be  dissolved,  but  not  gelatin  or 
horny  tis8U< 

(3.)  Starch  is  converted  into  ahi<->>sr  in  mi  exactly  similar  manner 
to  that  which  happens  with  the  saliva.  As  mentioned  befoiv.  it 
seems  not  unlikely  that  glucose  is  not  formed  at  once  from  starch, 
but  that  certain  dextrinea  are  intermediate  products.  If  the 
BUgar  which  is  at  first  formed,  as  is  stated  by  some  chemists* 
be  not  glucose  but  maltose,  at  any  rate  the  pancreatic  juice 
after  a  time  completes  the  whole  change  of  starch  into  glucose. 
There  is  a  distinct  amylolytic  ferment  (Amylopsin)  in  the  pan- 
creatic juice  which  cannot  be  distinguished  from  ptyalin. 

(4.)  Oils  and  fats  are  both  emulsified  and  split  up  into  their  fatty 
acids  and  glycerin  by  pancreatic  secretion.  Even  if  part  of  this 
action  is  due  to  the  alkinity  of  the  medium,  it  is  probable  that 
there  is  a  third  distinct  ferment  (Steapsin)  which  facilitates  the 
change. 

Several  cases  have  been  recorded  in  which  the  pancreatic  duct 
being  obstructed,  so  that  its  secretion  could  not  be  discharged, 
fatty  or  oily  matter  was  abundantly  discharged  from  the  intes- 
tines. In  nearly  all  these  cases,  indeed,  the  liver  was  coincidently 
diseased,  and  the  change  or  absence  of  the  bile  might  appear  to 
contribute  to  the  result ;  }*et  the  frequency  of  extensive  disease 
of  the  liver,  unaccompanied  by  fatty  discharges  from  the  intes- 
tines, favours  the  view  that,  in  these  cases,  it  is  to  the  absence 
of  the  pancreatic  fluid  from  the  intestines  that  the  excretion  or 
non-absorption  of  fatty  matter  should  be  ascribed. 

(5.)  It  ])Ossesses  the  property  of  curdling  mUJc,  containing  a 
special  (rennet)  ferment  for  that  purpose.  The  ferment  is  dis- 
tinct from  trypsin,  and  will  act  in  the  presence  of  an  acid  ( W. 
Roberts). 

Conditions  favourable  to  the  Action  of  the  Pancreatic 
Juice. — These  are  similar  to  those  which  are  favourable  to  the 
action  of  the  saliva,  and  the  reverse  (p.  285). 


33^ 


DIGESTION. 


[chap.  VIII. 


The  Liver. 

The  Liver,  the  largest  gland  in  the  body,  situated  in  the 
abdomen,  chiefly  on  the  right  side,  is  an  extremely  vascular 
organ,  and  receives  its  supply  of  blood  from  two  distinct 
vessels,  the  portal  vein  and  hepatic  artery,  while  the  blood  is 
returned  from  it  into  the  vena  cava  inferior  by  the  hepatic 
veins.  Its  secretion,  the  bile,  is  conveyed  from  it  b}T  the  hepatic 
duct,  either  directly  into  the  intestine,  or,  when  digestion  is  not 


Fi°-.  196. — The  under  surface  of  tic  liver,  a.  b.,  gall-bladder ;  h.  d.,  common  bile-duct : 
*H.  a.,  hepatic  arteiy.  v.  p.,  portal  vein;  l.  q..  lobulus  quadratus  ;  l.  s.,  lobulus 
spigelii ;  l.  c,  lobulus  caudatus  ;  d.  v.,  ductus  venosus ;  u.  v.,imibilical  vein.  (Noble 
Smith.) 


going  on,  into  the  cystic  duct,  and  thence  into  the  gall-bladder, 
where  it  accumulates  until  required.  The  portal  vein,  hepatic 
artery,  and  hepatic  duct  branch  together  throughout  the  liver, 
while  the  hepatic  veins  and  their  tributaries  run  by  themselves. 

On  the  outside  the  liver  has  an  incomplete  covering  of  peri- 
toneum, and  beneath  this  is  a  very  fine  coat  of  areolar  tissue,  con- 
tinuous over  the  whole  surface  of  the  organ.  It  is  thickest 
where  the  peritoneum  is  absent,  and  is  continuous  on  the  general 
surface  of  the  liver  with  the  fine,  and,  in  the  human  subject, 
almost  imperceptible,  areolar  tissue  investing  the  lobules.  At 
the  transverse  fissure  it  is  merged  in  the  areolar  investment 
called   Glisson's   capsule,    which,    surrounding   the   portal    vein, 


I  1I.W.    VIII. J 


THE   LIVER. 


3->  *> 


hepatic  artery,  and  hepatic  duct,  aa  they  enter  at  thia  part,  ac- 
companies them  in  their  b  ran<  jhinga  through  the  substance  of 
the  liver. 

Structure. — The  liver  is  made  up  of  small  roundish  or  oval 
portions  called  lobules,  each  of 
which  is  aboul  ',,  of  an  inch  in 
diameter,  and  com]  osed  of  the 
minute  branches  of  the  portal 
vein,  hepatic  artery,  hepatic  duct, 
and  hepatic  vein  ;  while  the  intcr- 
stices  of  these  vessels  are  filled 
by  the  liver  cells.  The  hepatic 
cells  (fig.  197),  which  form  the 
glandular   or    secreting   part    of 

the  liver,    are   of    a    spheroidal  form,  somewhat    polygonal    from 
mutual  pressure  about  -^  to  T^o  inch  iu  diameter,  possessing 


Fi„  107.— A.  I       -  B.  Ditto,  con- 

taining various  .-bced  particles  of  fat. 


Fig   198  —I  "?'  canal,  containing  a  portal  vein,  hepatic  artery  and 

hepatic  duct,  from  the  pig.  p,'  branch  of  vena  port«>,  situate  in  a  portal  .anal  lormed 
amongst  the  lobules  of  the  liver,  I  1,  and  giving  off  vaginal  branches  ;  there  are  also 
seen  within  the  large  portal  vein  numerous  orihees  of  the  smallest  interlobular  veins 
arising  directly  from  it ;  a,  hepatic  artery ;  d,  hepatic  duct,     x  5.     (Kiernan.) 


one,  sometimes  two  nuclei.     The  cell-substance  contains  numerous 
fatty  molecules,  and  some  yellowish-brown  granules  of  bile-pigment. 


334 


DIGESTION. 


[CHAP.  VIII. 


The  cells  sometimes  exhibit  slow  amoeboid  movements.  They  are 
held  together  by  a  very  delicate  sustentacular  tissue,  continuous 
with  the  interlobular  connective  tissue. 

To  understand  the  distribution  of  the  blood-vessels  in  the 
liver,  it  will  be  well  to  trace,  first,  the  two  blood-vessels  and  the 
duct  which  enter  the  organ  on  the  under  surface  at  the  transverse 
fissure,  viz.,  the  portal  vein,  hepatic  artery,  and  hepatic  duct.  As 
before  remarked,  all  three  run  in  company,  and  their  appearance 
on  longitudinal  section  is  shown  in  fig.  198.  Running  together 
through  the  substance  of  the  liver,  they  are  contained  in  small 
channels  called  portal  canals,  their  immediate  investment  being 
a  sheath  of  areolar  tissue  (Glisson's  capsule). 

To  take  the  distribution  of  the  portal  vein  first : — In  its 
course  through   the   liver  this  vessel   gives    off  small   branches 


Fig.  109. — Cross  section  of  a  lobule  of  the  human  liver,  in  which  the  capillary  network  between 
the  portal  and  hepatic  veins  has  been  fully  injected,  i,  section  of  the  ;'/^/77-lobular 
vein;  2,  its  smaller  branches  collecting  blood  from  the  capillary  network;  3.  inter- 
lobular branches  of  the  vena  porta?  with  their  smaller  ramifications  passing  inwards 
towards  the  capillary  network  in  the  substance  of  the  lobule,     x  60.     (Sappey.) 


which  divide  and  subdivide  between  the  lobules  surrounding 
them  and  limiting  them,  and  from  this  circumstance  called 
inter-lobukur  veins.  From  these  small  vessels  a  dense  capillary 
network  is  prolonged  into  the  substance  of  the  lobule,  and  this 
network,  gradually  gathering  itself  up,  so  to  speak,  into  larger 


CHAl".  VIII.] 


THE    LIVER. 


335 


Is,  converges  finally  to  a  single  small  vein,  occupying  the 
centre  of  the  lobule,  and  hence  called  mtfra-lobular.    Tliis  arrange 
nient  is  well  Been  in  fig.  199,  which  represents  a  transverse  section 
of  a  lobule. 

The  small  inlro-lobular  veins  discharge  their  contents  into 
veins  called  ^-lobular  (hhh,  fig.  200) ;  while  these  again,  by  their 
union,  form  the  main  branches  of  the  hepatic  veins,  which  leave 


Fig.  200. — Section  of  a  portion  of  liver  passing  longitudinally  through  a  considerable  hepatic 
vein,  from  the  pig.  H,  hepatic  venous  trunk,  against  which  the  sides  of  the  lobules  (/) 
are  applied  ;  h,  h,  h,  sublobular  hepatic  veins,  on  which  the  bases  of  the  lobules  rest, 
and  through  the  coats  of  which  they  are  seen  as  polygonal  figures ;  ?',  mouth  of  the 
intralobular  veins,  opening  into  the  sublobular  veins ;  %'.  intralobular  veins  shown 
passing  up  the  centre  of  some  divided  lobules  ;  /,  /,  cut  sm-face  of  the  liver ;  c,  c,  wails 
of  the  hepatic  venous  canal,  formed  by  the  polygonal  bases  of  the  lobules,  x  5. 
(Kiernan.) 

the  posterior  border  of  the  liver  to  end  by  two  or  three  principal 
trunks  in  the  inferior  vena  cava,  just  before  its  passage  through 
the  diaphragm.  The  swMobular  and  hepatic  veins,  unlike  the 
portal  vein  and  its  companions,  have  little  or  no  areolar  tissue 
around  them,  and  their  coats  being  very  thin,  they  form  little 
more  than  mere  channels  in  the  liver  substance  which  closely 
surrounds  them. 

The   manner   in   which   the   lobules    are  connected    with   the 
nib4obular  veins  by  means  of  the  small  intralobular  veins  is  well- 


33$ 


DIGESTION. 


[CHAP.  VIII. 


seen  in  the  diagram  (fig.  200  and  in  fig.  201),  which  represent  the 
parts  as  seen  in  a  longitudinal  section.     The  appearance  has  been 

likened  to  a  twig  having  leaves  with- 
out footstalks — the  lobules  representing 
the  leaves,  and  the  sub-lobidar  vein  the 
small  branch  from  which  it  springs. 
On  a  transverse  section,  the  appearance 
of  the  intra-lobular  veins  is  that  of  1, 
ibui*.      ^S-  j99j  Avhil°   both  a  transverse   and 


Longitudinal    section    are    exhibited  in 
fig.  176. 

The  hepatic  artery,  the  function  of 
which  is  to  distribute  blood  for  nutri- 
tion to  Glisson's  capsule,  the  walls  of 
the  ducts  and  blood-vessels,  and  other 
parts  of  the  liver,  is  distributed  in  a 
very  similar  manner  to  the  portal  vein, 
its  blood  being  returned  b}T  small 
branches  either  into  the  ramifications 

of  the  portal   vein,    or  into  the  capillary  plexus  of  the   lobules 

which  connects  the  inter-  and  wrtra-lobular  veins. 


Lobule 


Fig.    201. — Diagram    showing    the 
manner  in  which  the  lobules  of  the 

■  •"  on  the  sublobular 
(After  Kiernan.) 


p  h 

Fig.  202.— Capillary  network  of  the  lobules  of  the  rabbit's  liver.  The  figure  is  taken  from  a 
very  successful  injection  of  the  hepatic  veins,  made  by  Halting  :  it  shows  nearly  the 
whole  of  two  lobules,  and  parts  of  three  others  ;  p,  portal  branches  running  in  the 
interlobular  spaces  ;  h,  hepatic  veins  penetrating  and  radiating  from  the  centre  of  the 
lobules,     x  45.     (Kolliker.) 

The  hepatic  duct  divides  and  subdivides  in  a  manner  very  like 
that  of  the  portal  vein  and  hepatic  artery,  the  larger  branches 


en  \i\   \  in.  | 


STRUCTURE    <>!•'    LIVER. 


337 


being  lined   by  cylindrical,  and   the  smaller  by  small  polygonal 
epithelium. 

The  bile-capillaries  commence  between  the  hepatic  cells,  and 
are  bounded  by  a  delicate  membranous 

wall  of  their  own.  They  appeal'  to  be 
always  bounded  by  hepatic  cells  on  all 
sides,  and  are  thus  separated  from  the 
nearest  blood-capillary  by  at  least  the 
breadth  of  one  cell  (figs.  203  and  204). 

The  Gall-bladder  .—The  ( !  all-bla.  1 
der  (g,  b,  fig.  196)  is  a  pyriform  bag, 
attached  to  the  under  surface  of  the 
liver,  and  supported  also  by  the  peri- 
toneum, which  passes  below  it.  The 
larger  end  or  fundus,  projects  beyond 
the  front  margin  of  the  liver;  while 
the  smaller  end  contracts  into  the 
cystic  duct. 

Structure. — The  walls  of  the  gall- 
bladder are  constructed  of  three  princi- 
pal coats.  (1)  Externally  (excepting  that 
part  which  is  in  contact  with  the  liver), 
is  the  serous  coat,  which  has  the  same 

structure  as  the  peritoneum  with  which  it  is  continuous.     Within 
this  is  (2)  the  fibrous  or  areolar  coat,  constructed  of  tough  fibrous 


Fig".  203. —  Portion  of  a  lobnlr  of 
liver,  a,  bile  capillaries  between 
liver-cells,  the  network  in 
which  is  well  seen  ;  b,  blood 
capillaries,  x  350.  (Klein  and 
Noble  Smith.) 


Fig.  204. — Hepatic  cells  and  bile  capillaries,  from  the  liver  of  a  child  three  months  old. 
Both  figures  represent  fragments  of  a  section  carried  through  the  periphery  of  a  lobule. 
The  red  corpuscles  of  the  blood  are  recognized  by  their  circular  contour:  vp,  corre- 
sponds to  an  interlobular  vein  in  immediate  proximity  with  which  are  the  epithelial 
cells  of  the  biliary  ducts,  to  which,  at  the  lower  part  of  the  figures,  the  much  larger 
hepatic  cells  suddenly  succeed.     (E.  Hering.) 


338  DIGESTION.  [chap.  viii. 

and  clastic  tissue,  with  which  is  mingled  a  considerable  number 
of  plain  muscular  fibres,  both  longitudinal  and  circular.  (3)  In- 
ternally the  gall-bladder  is  lined  by  mucous  membrane,  and  a 
layer  of  columnar  epithelium.  The  surface  of  the  mucous  mem- 
brane presents  to  the  naked  eye  a  minutely  honeycombed  ap- 
pearance from  a  number  of  tiny  polygonal  depressions  with 
intervening  ridges,  by  which  its  surface  is  mapped  out.  In  the 
cystic  duct  the  mucous  membrane  is  raised  up  in  the  form  of 
crescentic  folds,  which  together  appear  like  a  spiral  valve,  and 
which  minister  to  the  function  of  the  gall-bladder  in  retaining 
the  bile  during  the  intervals  of  digestion. 

The  gall-bladder  and  all  the  main  biliary  ducts  are  provided 
with  mucous  glands,  which  open  on  their  internal  surface. 

Functions  of  the  Liver. — The  functions  of  the  Liver  may  be 
classified  under  the  following  heads  : — 1.  The  Secretion  of  Bile. 
2.  The  Elaboration  of  Blood ;  under  this  head  ma}7  be  included 
the  Glycogenic  Function. 


I.  The  Secretion  of  Bile. 

Properties  of  the  Bile. — The  bile  is  a  somewhat  viscid  fluid, 
of  a  yellow  or  reddish-yellow  colour,  a  strongly  bitter  taste,  and, 
when  fresh,  with  a  scarcely  perceptible  odour  :  it  has  a  neutral  or 
slightly  alkaline  reaction,  and  its  specific  gravity  is  about  1020. 
Its  colour  and  degree  of  consistence  vary  much,  apparently  inde- 
pendent of  disease  ;  but,  as  a  rule,  it  becomes  gradually  more 
deeply  coloured  and  thicker  as  it  advances  along  its  ducts,  or 
when  it  remains  long  in  the  gall-bladder,  wherein,  at  the  same 
time,  it  becomes  more  viscid  and  ropy,  of  a  darker  colour,  and 
more  bitter  taste,  mainly  from  its  greater  degree  of  concentration, 
on  account  of  partial  absorption  of  its  water,  but  partly  also  from 
being  mixed  with  mucus. 

Chemical  Composition  of  Human  Bile.     (Frerichs.) 

Water 859-2 

Solids 140-8 

iooo-o 


oh  ip.  viii.]  Bl LE.  ^-?o 

Bile  salts  or  Bilin 91-5 

Fat 9-2 

Cholesterin     .........  26 

Mucus  and  colouring  matters    .        .        .        .        .     .  29^8 

Baits 7.7 


1408 


Bile  salts,  or  Bilin,  can  be  obtained  as  colourless,  exceedingly 
deliquescent  crystals,  soluble  in  water,  alcohol,  and  alkaline  solu- 
tions, giving  to  the  watery  solution  the  taste  and  general  characters 
of  bile.  Thc}r  consist  of  sodium  salts  of  glycocholic  and  tauro- 
cholic  acids.  The  former  salt  is  composed  of  cholic  acid  conjugated 
with  glycin  (see  Appendix),  the  latter  of  the  same  acid  conjugated 
with  taurin.  The  proportion  of  these  two  salts  in  the  bile  of 
■different  animals  varies,  e.g.,  'in  ox  bile  the  glycocholate  is  in 
great  excess,  whereas  the  bile  of  the  dog,  cat,  bear,  and  other  car- 
nivora  contains  taurocholate  alone  ;  inhuman  bile  both  are  present 
in  about  the  same  amount  (glycocholate  in  excess  }). 

Preparation  of  Bile  Salt. — Bile  salts  may  be  prepared  in  the 
following  manner  :  mix  bile  which  has  been  evaporated  to  a  quarter 
of  its  bulk  with  animal  charcoal,  and  evaporate  to  perfect  dryness 
in  a  water  bath.  Next  extract  the  mass  whilst  still  warm  with 
absolute  alcohol.  Separate  the  alcoholic  extract  by  filtration,  and 
to  it  add  perfectly  anhydrous  ether  as  long  as  a  precipitate  is 
thrown  down.  The  solution  and  precipitate  should  be  set  aside  in 
a  closely  stoppered  bottle  for  some  days,  when  ciystals  of  the  bile 
salts  or  bilin  will  have  separated  out.  The  glycocholate  may  be 
separated  from  the  taurocholate  by  dissolving  bilin  in  water,  and 
adding  to  it  a  solution  of  neutral  lead  acetate,  and  then  a  little 
basic  lead  acetate,  when  lead  glycocholate  separates  out.  Filter 
and  add  to  the  filtrate  lead  acetate  and  ammonia,  a  precipitate 
of  lead  taurocholate  will  be  formed,  which  may  be  filtered  off.  In 
both  cases,  the  lead  may  be  got  rid  of  by  suspending  or  dissolving 
in  hot  alcohol,  adding  hydrogen  sulphate,  filtering  and  allowing 
the  acids  to  separate  out  by  the  addition  of  water. 

The  test  for  bile  salts  is  known  as  Pettenkofer's.  If  to  an 
aqueous  solution  of  the  salts  strong  sulphuric  acid  be  added,  the 
bile  acids  are  first  of  all  precipitated,  but  on  the  further  addition 

z  2 


340  DIGESTION.  [chap.  vnr. 

of  the  acid  are  re-dissolved.     Tf  to  the  solution  a  drop  of  solu- 
tion of  cane  sugar  be  added,  a  fine  purple  colour  is  developed. 

The  re-action  will  also  occur  on  the  addition  of  grape  or  fruit  sugar  instead 
of  cane  sugar,  slowly  with  the  first,  quickly  with  the  last ;  and  a  colour  similar 
to  the  above  is  produced  by  the  action  of  sulphuric  acid  and  sugar  on  albu- 
men, the  crystalline  lens,  nerve  tissue,  oleic  ncid.  pure  ether,  cholestcrin. 
morphia,  codeia  and  amylic  alcohol. 

The  spectrum  of  Pettenkofer's  reaction,  when  the  fluid  is 
moderately  diluted,  shows  four  hands — the  most  marked  and 
largest  at  E,  and  a  little  to  the  left  ;  another  at  F.  ;  a  third 
between  D  and  E,  nearer  to  D  ;   and  the  fourth  near  D. 

The  yellow  colouring  matter  of  the  bile  of  man  and  the  Carnivora 
is  termed  Bilirubin  or  Bilifulvin  (cl6  hi8  x2  o,)  crystallizable  and 
insoluble  in  water,  soluble  in  chloroform  or  carbon  disulphate  ;  a 
green  colouring  matter,  Biliverdin  (cl6  h20  x2  o.),  which  always 
exists  in  large  amount  in  the  bile  of  Herbivora,  being  formed 
from  bilirubin  on  exposure  to  the  air,  or  by  subjecting  the  bile  to 
any  other  oxidizing  agency,  as  by  adding  nitric  acid.  When  the 
bile  has  been  long  in  the  gall-bladder,  a  third  pigment,  Biliprasin, 
may  be  also  found  in  small  amount. 

In  cases  of  biliary  obstruction,  the  colouring  matter  of  the  bile 
is  re-absorbed,  and  circulates  with  the  blood,  giving  to  the  tissues- 
the  yellow  tint  characteristic  of  jaundice. 

The  colouring  matters  of  human  bile  do  not  appear  to  give 
characteristic  absorption  spectra ;  but  the  bile  of  the  guinea  pig,, 
rabbit,  mouse,  sheep,  ox,  and  crow  do  so,  the  most  constant  of 
which  appears  to  be  a  band  at  F.  The  bile  of  the  sheep  and  ox. 
give  three  bands  in  a  thick  layer,  and  four  or  five  bands  with 
a  thinner  layer,  one  on  each  side  of  D,  one  near  E,  and  a  faint 
line  at  F.     (McMunn). 

There  seems  to  be  a  close  relationship  between  the  colour- 
matter  of  the  blood  and  of  the  bile,  and  it  may  be  added,  between 
these  and  that  of  the  urine  (urobilin),  and  of  the  faeces  (ster- 
cobilin)  also ;  it  is  probable  they  are,  all  of  them,  varieties  of  the 
same  pigment,  or  derived  from  the  same  source.  Indeed  it  is 
maintained  that  Urobilin  is  identical  with  JIt/drobitiri/hin,  a  sub- 
stance which  is  obtained  from  bilirubin  by  the  action  of  sodium 


CHAP.  VIII.  1 


BILE. 


341 


amalgam,  or  bj  the  action  of  sodium  amalgam  on  alkaline 
hsematin;  both  urobilin  and  hydrobilirubin giving  a  characteristic 
absorption  band  between  band  F.  They  are  also  identical  with 
stercobilin,  which  is  formed  in  the  alimentary  canal  from  l»ile 
pigments. 

A  common  test  (Gmelin's)  for  the  presence  of  Ul  pigment  con 
BiBts  <>f  the  addition  of  a  small  quantity  of  nitric  acid,  yellow  with 
nitrous  acid  ;  if  bile  be  present,  a  play  of  colours  is  produced, 
beginning  with  green  and  passing  through  blue  and  violet  to  red, 
and  lastly  to  yellow.  The  spectrum  of  Gmelin's  test  gives  a  black 
band  extending  from  near  b  to  beyond  F. 

Fatty  substances  are  found  in  variable  proportions  in  the  bile. 
Besides  the  ordinary  saponifiable  fats,  there  is  a  small  quantity  of 
Cholesterin,  a  so-called  non-saponi- 
tiable  fat,  which,  with  the  other 
live  fats,  is  probably  held  in  solu- 
tion by  the  bile  salts.  It  is  a 
body  belonging  to  the  class  of 
monatomic  alcohols  (c26  h44  o), 
and  ciystallizes  in  rhombic  plates 
{tig.  205).  It  is  insoluble  in  water 
and  cold  alcohol,  but  dissolves 
easily  in  boiling  alcohol  or  ether. 
It  gives  a  red  colour  with  strong 
Bulphuric  acid,  and  with  nitric 
acid  and  ammonia  ;  also  a  play 
of  colours  beginning  with  blood 

red  and  ending  with  green  on  the  addition  of  sulphuric  acid  and 
chloroform.  Lecithin  (c44  h90  xro9),  a  phosphorus-containing  body 
and  Neurin  (cs  hi5  no2),  are  also  found  in  bile,  the  latter  probably 
as  a  decomposition  product  of  the  former. 

The  Mucus  in  bile  is  derived  from  the  mucous  membrane  and 
glands  of  the  gall-bladder,  and  of  the  hepatic  ducts.  It  consti- 
tutes the  residue  after  bile  is  treated  with  alcohol.  The  epithe- 
lium with  which  it  is  mixed  may  be  detected  in  the  bile  with 
the  microscope  in  the  form  of  cylindrical  cells,  either  scattered 
or  still  held  together  in  layers.  To  the  presence  of  the  mucus  is 
probably  to  be  ascribed  the  rapid  decomposition  undergone  by  the 


Fi#\  205. — ( 'rystalline  scales  of  ciholesti  rin. 


342  DIGESTION.  [chap.  yiii. 

bilin ;  for,  according  to  Berzelius,  if  the  mucus  be  separated,  bile 
will  remain  unchanged  for  many  days. 

The  Saline  or  inorganic  constituents  of  the  bile  are  similar  to 
those  found  in  most  other  secreted  fluids.  It  is  possible  that  the 
carbonate  and  neutral  phosphate  of  sodium  and  potassium,  found 
in  the  ashes  of  bile,- are  formed  in  the  incineration,  and  do  not 
exist  as  such  in  the  fluid.  Oxide  of  iron  is  said  to  be  a  common 
constituent  of  the  ashes  of  bile,  and  copper  is  generally  found  in 
healthy  bile,  and  constantly  in  biliary  calculi. 

Gas — A  certain  small  amount  of  carbonic  acid,  oxygen,  and 
nitrogen,  may  be  extracted  from  bile. 

Mode  of  Secretion  and  Discharge. —  The  process  of  secreting 
bile  is  continually  going  on,  but  appears  to  be  retarded  during 
fisting,  and  accelerated  on  taking  food.  This  has  been  shown  by 
tying  the  common  bile-duct  of  a  dog,  and  establishing  a  fistulous 
opening  between  the  skin  and  gall-bladder,  Avhereby  all  the  bile 
secreted  was  discharged  at  the  surface.  It  was  noticed  that  when 
the  animal  was  fasting,  sometimes  not  a  drop  of  bile  was  dis- 
charged for  several  hours  ;  but  that,  in  about  ten  minutes  after 
the  introduction  of  food  into  the  stomach,  the  bile  began  to  flow 
abundantly,  and  continued  to  do  so  during  the  whole  period  of 
digestion.      (Blondlot,  Bidder  and  Schmidt.) 

The  bile  is  formed  in  the  hepatic  cells  ;  then,  being  discharged 
into  the  minute  hepatic  ducts,  it  passes  into  the  larger  trunks, 
and  from  the  main  hepatic  duct  may  be  carried  at  once  into  the 
duodenum.  But,  probably,  this  happens  only  while  digestion  is 
going  on  ;  during  fasting,  it  regurgitates  from  the  common  bile- 
duct  through  the  cystic  duct,  into  the  gall-bladder,  where  it  accu- 
mulates till,  in  the  next  period  of  digestion,  it  is  discharged  into 
the  intestine.  The  gall-bladder  thus  fulfils  what- appears  to  be  its 
chief  or  only  office,  that  of  a  reservoir  ;  for  its  presence  enables 
bile  to  be  constantly  secreted,  }-et  insures  its  employment  in  the 
service  of  digestion,  although  digestion  is  periodic,  and  the  secre- 
tion of  bile  constant. 

The  mechanism  by  which  the  bile  passes  into  the  gall-bladder 
is  simple.  The  orifice  through  which  the  common  bile-duct  com- 
municates with  the  duodenum  is  narrower  than  the  duct,  and 
appears  to  be  closed,  except  when    there  is    sufficient   pressure 


chap,  viii.]  SECRETION    OF    BILE.  343 

behind  to  force  the  bile  through  it.  The  pressure  exercised  upon 
the  bile  secreted  during  the  intervals  of  digestion  appears  insuffi- 
cient to  overcome  the  force  with  which  the  orifice  of  the  duct  is 

closed  ;  and  the  bile  in  the  common  duct,  finding  no  exit  in  the 
intestine,  traverses  the  cystic  duct,  and  so  passes  into  the  gall- 
bladder, being  probably  aided  in  this  retrograde  course  by  the 
peristaltic  action  of  the  ducts.  The  bile  is  discharged  from  the 
gall-bladder  and  enters  the  duodenum  on  the  introduction  of 
food  into  the  small  intestine  :  being  pressed  on  by  the  contrac- 
tion of  the  coats  of  the  gall-bladder,  and  of  the  common  bile- 
duct  also;  for  both  these  organs  contain  unstriped  muscular 
fibre-cells.  Their  contraction  is  excited  by  the  stimulus  of  the 
food  in  the  duodenum  acting  so  as  to  produce  a  reflex  movement, 
the  force  of  which  is  sufficient  to  open  the  orifice  of  the  common 
bile-duct. 

Bile,  as  such,  is  not  pre-formed  in  the  blood.  As  just  observed, 
it  is  formed  by  the  hepatic  cells,  although  some  of  the  material  may 
be  brought  to  them  almost  in  the  condition  for  immediate  secretion. 
When  it  is,  however,  prevented  by  an  obstruction  of  some  kind, 
from  escaping  into  the  intestine  (as  by  the  passage  of  a  f/all-stone 
along  the  hepatic  duct)  it  is  absorbed  in  great  excess  into  the 
blood,  and,  circulating  with  it,  gives  rise  to  the  well-known 
phenomena  of  jaundice.  This  is  explained  by  the  fact  that  the 
pressure  of  secretion  in  the  ducts  is  normally  very  low,  and  if  it 
exceeds  -?-  inch  of  mercury  (16  mm.)  the  secretion  ceases  to  be 
poured  out,  and  if  the  opposing  force  be  increased,  the  bile  finds 
its  way  into  the  blood. 

Quantity. — Various  estimates  have  been  made  of  the  quantity- 
of  bile  discharged  into  the  intestines  in  twenty-four  hours  :  the 
quantity  doubtless  varying,  like  that  of  the  gastric  fluid,  in  pro- 
portion to  the  amount  of  food  taken.  A  fair  average  of  several 
computations  would  give  20  to  40  oz.  (600  —  900  cc.)  as  the 
quantity  daily  secreted  by  man. 

Uses. — (1)  As  an  excre?nentitious  substance,  the  bile  may  serve 
especially  as  a  medium  for  the  separation  of  excess  of  carbon  and 
hydrogen  from  the  blood  ;  and  its  adaptation  to  this  purpose  is 
well-illustrated  by  the  peculiarities  attending  its  secretion  and 
disposal  iu  the  foetus.     During  intra-utcrine  life,  the  lungs  and 


344  DIGESTION.  [chap.  viij. 

the  intestinal  canal  are  almost  inactive  ;  there  is  no  respiration  of 
open  air  or  digestion  of  food  ;  these  are  unnecessary,  on  account 
of  the  supply  of  well  elaborated  nutriment  received  by  the  vessels 
of  the  foetus  at  the  placenta.  The  liver,  during  the  same  time,  is 
proportionately  larger  than  it  is  after  birth,  and  the  secretion  of 
bile  is  active,  although  there  is  no  food  in  the  intestinal  canal 
upon  which  it  can  exercise  any  digestive  property.  At  birth,  the 
intestinal  canal  is  full  of  thick  bile,  mixed  with  intestinal  secre- 
tion ;  the  meconium,  or  fa?ces  of  the  foetus,  containing  all  the 
essential  principles  of  bile. 

('•imposition  of  Meconium  (Frerichs)  : 

Biliary  resin 15 '6 

Common  fat  and  cholesterin  .         .         .         .     .  15  "4 

Epithelium,  mucus,  pigment,  and  salts        .         .  69/0 


lOO'O 


In  the  foetus,  therefore,  the  main  purpose  of  the  secretion  of  bile 
must  be  the  purification  of  blood  by  direct  excretion,  i.e.,  by 
separation  from  the  blood,  and  ejection  from  the  body  without 
further  change.  Probablv  all  the  bile  secreted  in  fcetal  life  is 
incorporated  in  the  meconium,  and  with  it  discharged,  and  thus 
the  liver  may  be  said  to  discharge  a  function  in  some  sense 
vicarious  of  that  of  the  lungs.  For,  in  the  foetus,  nearly  all  the 
blood  coming  from  the  placenta  passes  through  the  liver,  previous 
to  its  distribution  to  the  several  organs  of  the  body ;  and  the 
abstraction  of  carbem,  hydrogen,  and  other  elements  of  bile  will 
purify  it,  as  in  extra-uterine  life  it  is  purified  by  the  separation 
of  carbonic  acid  and  water  at  the  lungs. 

The  evident  disposal  of  the  foetal  bile  by  excretion,  makes  it 
highly  probable  that  the  bile  in  extra-uterine  life  is  also,  at  least 
in  part,  destined  to  lie  discharged  as  excrementitious.  The 
analysis  of  the  freces  of  both  children  and  adults  shows  that 
(except  when  rapidly  discharged  in  purgation)  they  contain  very 
little  of  the  bile  secreted,  probably  not  more  than  one-sixteenth 
part  of  its  weight,  and  that  this  portion  includes  chiefly  its 
colouring,  and  some  of  its  fatty  matters,  and  to  only  a  very 
slight  degree,  its  salts,  almost  all  of  which  have  been  re-absorbed 
from  the  intestines  into  the  blood. 


i   HAP.    \  111. 


USES    OF    BILE.  345 


The  elementary  composition  of  bile  salts  shows,  however,  Buch 
a   preponderance  of  carbon  and  hydrogen,  that  probably,   after 

absorption,  it  combines  with  oxygen,  and  is  excreted  in  the  form 
of  carbonic   acid  and  water.     The  change  after  birth,  from  the 

direct  to  the  indirect  mode  of  excretion  of  the  bile  may,  with 
much  probability,  be  connected  with  a  purpose  in  relation  to  the 
development  of  heat.  The  temperature  of  the  foetus  is  maintained 
by  that  of  the  parent,  and  needs  no  source  of  heat  within  itself; 
but,  in  extra-uterine  life,  there  is  (as  one  may  say)  a  waste  of 
material  for  heat  when  any  excretion  is  discharged  unoxidized  ; 
the  carbon  and  hydrogen  of  the  bilin,  therefore,  instead  of 
being  ejected  in  the  faeces,  are  re-absorbed,  in  order  that  they 
may  be  combined  with  oxygen,  and  that  in  the  combination  heat 
may  be  generated. 

A  substance,  which  has  been  discovered  in  the  fieces,  and  named 
stt  rcorin  is  closely  allied  to  cholesterin  ;  and  it  lias  been  suggested 
that  while  one  great  function  of  the  liver  is  to  excrete  cholesterin 
from  the  blood,  as  the  kidney  excretes  urea,  the  stercorin  of  faeces 
is  the  modified  form  in  which  cholesterin  finally  leaves  the 
body.  Ten  grains  and  a  half  of  stercorin  are  excreted  daily 
(A.  Flint). 

From  the  peculiar  manner  in  which  the  liver  is  supplied  with 
much  of  the  blood  that  flows  through  it,  it  is  probable  that  this 
organ  is  excretory,  not  only  for  such  hydro-carbonaceous  matters 
as  may  need  expulsion  from  any  portion  of  the  blood,  but  that  it 
serves  for  the  direct  purification  of  the  stream  which,  arriving  by 
the  portal  vein,  has  just  gathered  up  various  substances  in  its 
course  through  the  digestive  organs — substances  which  may  need 
to  be  expelled,  almost  immediately  after  their  absorption.  For  it 
is  easily  conceivable  that  many  things  may  be  taken  up  during 
digestion,  which  not  only  are  unfit  for  purposes  of  nutrition,  but 
which  would  be  positively  injurious  if  allowed  to  mingle  with  the 
general  mass  of  the  blood.  The  liver,  therefore,  may  be  supposed 
placed  in  the  only  road  by  which  such  matters  can  pas.-,  unchanged 
into  the  general  current,  jealously  to  guard  against  their  further 
progress,  and  turn  them  back  again  into  an  excretory  channel. 
The  frequency  with  which  metallic  poisons  are  either  excreted 
by  the  liver,  or  intercepted   and   retained,  often  for  a  considerable 


346  DIGESTION.  [chap.  vm. 

time,  in  its  own  substance,  may  be  adduced  as  evidence  for  the 
probable  truth  of  this  supposition. 

(2).  As  a  digestive  fluid. — Though  one  chief  purpose  of  the 
secretion  of  bile  may  thus  appear  to  be  the  purification  of 
the  blood  by  ultimate  excretion,  yet  there  are  many  reasons  for 
believing  that,  while  it  is  in  the  intestines  it  performs  an 
important  part  in  the  process  of  digestion.  In  nearly  all 
animals,  for  example,  the  bile  is  discharged,  not  through  an 
excretory  duct  communicating  with  the  external  surface  or 
with  a  simple  reservoir,  as  most  excretions  are,  but  is  made  to 
pass  into  the  intestinal  canal,  so  as  to  be  mingled  with  the 
chyme  directly  after  it  leaves  the  stomach ;  an  arrangement, 
the  constancy  of  which  clearly  indicates  that  the  bile  has  some 
important  relations  to  the  food  with  which  it  is  thus  ruixed- 
A  similar  indication  is  furnished  also  by  the  fact  that  the  secre- 
tion of  bile  is  most  active,  and  the  quantity  discharged  into  the 
intestines  much  greater,  during  digestion  than  at  any  other  time; 
although,  without  doubt,  this  activity  of  secretion  during  dieres- 
tion  may,  however,  be  in  part  ascribed  to  the  fact  that  a  greater 
quantity  of  blood  is  sent  through  the  portal  vein  to  the  liver  at 
this  time,  and  that  this  blood  contains  some  of  the  materials  of 
the  food  absorbed  from  the  stomach  and  intestines,  which  may 
need  to  be  excreted,  either  temporarily,  (to  be  afterwards  re- 
absorbed,) or  permanently. 

Respecting  the  functions  discharged  by  the  bile  in  digestion, 
there  is  little  doubt  that  it  (a.)  assists  in  emulsifying  the  fatty 
portions  of  the  food,  and  thus  rendering  them  capable  of  being 
absorbed  by  the  lacteals.  For  it  has  appeared  in  some  experiments 
in  which  the  common  bile-duct  was  tied,  that,  although  the  process 
of  digestion  in  the  stomach  was  unaffected,  chyle  was  no  longer 
well  formed ;  the  contents  of  the  lacteals  consisting  of  clear, 
colourless  fluid,  instead  of  being  opaque  and  white,  as  they 
ordinarily  are,  after  feeding. 

(6.)  It  is  probable,  also,  that  the  moistening  of  the  mucous  mem- 
brane of  the  intestines  by  bile  facilitates  absorption  of  fatty  matters 
through  it. 

(c.)  The  bile,  like  the  gastric  fluid,  has  a  considerable  anti- 
septic power,  and  may  serve  to  prevent  the  decomposition  of  food 


chap.  viu.  |  USES  OF  BILE.  •  347 

during  the  time  of  its  Bojourn   in   the   intestines.     Experiments 
show  that   the  contents  of  the  intestines  are   much  more  foetid 
after  the  common  bile-duct   lias  been  tied  than  at   other  tim< 
moreover,  it  is  found  that  the  mixture  of  bile  with  a   fermentine 
fluid  stops  or  spoils  the  process  of  fermentation. 

((/.)  The  bile  has  also  been  considered  to  act  as  a  natural 
purgative,  by  promoting  an  increased  secretion  of  the  intestinal 
glands,  and  by  stimulating  the  intestines  to  the  propulsion  of 
their  contents.  This  view  receives  support  from  the  constipation 
which  ordinarily  exists  in  jaundice,  from  the  diarrhoea  which 
accompanies  excessive  secretion  of  bile,  and  from  the  purgative 
properties  of  ox-gall. 

(e.)  The  bile  appears  to  have  the  power  of  precipitating  th< 
gastric  parapeptones  and  j>ej>tones,  tor/ether  with  the  pepsin  which 
is  mixed  up  with  them,  as  soon  as  the  contents  of  the  stomach 
meet  it  in  the  duodenum.  The  purpose  of  this  operation  is 
probably  both  to  delay  any  change  in  the  parapeptones  until  the 
pancreatic  juice  can  act  upon  them,  and  also  to  prevent  the  pepsin 
from  exercising  its  solvent  action  on  the  ferments  of  the  pancreatic 
juice. 


Nothing  is  known  with  certainty  respecting  the  changes  which 
the  re-absorbed  portions  of  the  bile  undergo.  That  they  are 
much  changed  appears  from  the  impossibility  of  detecting  them 
in  the  blood ;  and  that  part  of  this  change  is  effected  in  the  liver 
is  probable  from  an  experiment  of  Magendie,  who  found  that 
when  he  injected  bile  into  the  portal  vein,  a  dog  was  unharmed, 
but  was  killed  when  he  injected  the  bile  into  one  of  the  systemic 
vessels. 


II.  The  Liver  as  a  Blood-elaborating  Gland. 

The  secretion  of  bile,  as  already  observed,  is  only  one  of  the 
purposes  fulfilled  by  the  liver.  Another  very  important  function 
appears  to  be  that  of  so  acting  upon  certain  constituents  of  the 
blood  passing  through  it,  as  to  render  some  of  them  capable  of 
assimilation  with  the  blood  generally,  and  to  prepare  others  for 
being  duly  eliminated  in  the  process  of  respiration.      It  appears. 


348  DIGESTION,  [chap.  viii. 

that  the  peptones,  conveyed  from  the  alimentary  canal  by  the 
blood  of  the  portal  vein,  require  to  be  submitted  to  the  influence 

of  the  liver  before  they  can  he  assimilated  by  the  blood  ;  for  if 
.such  albuminous  matter  is  injected  into  the  jugular  vein,  it 
speedily  appears  in  the  urine  :  but  if  introduced  into  the  portal 

vein,  and  thus  allowed  to  traverse  the  liver,  it  is  no  longer 
ejected  as  a  foreign  substance,  but  is  incorporated  with  the  albu- 
minous part  of  the  blood.  Albuminous  matters  are  also  subject 
to  decomposition  by  the  liver  in  another  way  to  be  immediately 
noticed  (p.  349).  The  formation  of  urea  by  the  liver  will  he 
again  referred  to  (p.  457). 

Glycogenic  Function. — One  of  the  chief  uses  of  the  liver  in 
connection  with  elaboration  of  the  blood  is  comprised  in  what  is 
known  as  its  glycogenic  function.  The  important  fact  that  the  liver 
normally  forms  glucose  or  grape  sugar,  or  a  substance  readily  con- 
vertible into  it,  was  discovered  by  Claude  Bernard  in  the  course  of 
some  experiments  which  he  undertook  for  the  purpose  of  finding  out 
in  what  part  of  the  circulatory  system  the  saccharine  matter  dis- 
appeared, which  was  absorbed  from  the  alimentary  canal.  With 
this  purpose  he  fed  a  dog  for  seven  days  with  food  containing  a 
large  quantity  of  sugar  and  starch  ;  and,  as  might  be  expected,  found 
sugar  in  both  the  portal  and  hepatic  veins.  He  then  fed  a  dog 
with  meat  only,  and,  to  his  surprise,  still  found  sugar  in  the 
hepatic  veins.  Repeated  experiments  gave  invariably  the  same 
result  ;  no  sugar  being  found,  under  a  meat  diet,  in  the  portal 
.vein,  if  care  were  taken,  by  applying  a  ligature  on  it  at  the 
transverse  fissure,  to  prevent  reflux  of  blood  from  the  hepatic 
venous  system.  Bernard  found  sugar  also  in  the  substance  of  the 
liver.  It  thus  seemed  certain  that  the  liver  formed  sugar,  even 
when,  from  the  absence  of  saccharine  and  amyloid  matters  in  the 
food,  none  could  be  brought  directly  to  it  from  the  stomach  or 
intestines. 

Excepting  cases  in  which  large  quantities  of  starch  and  sugar 
were  taken  as  food,  no  sugar  was  found  in  the  blood  after  it  had 
passed  through  the  lungs  :  the  sugar  formed  by  the  liver,  having 
presumably  disappeared  by  combustion,  in  the  course  of  the 
pulmonary  circulation. 

Bernard  found,  subsequently  to  the  before-mentioned  experi- 
ments, that  a  liver,  removed  from  the  body,  and  from  which  all 


chap,  viu.]        GLYCOGENIC    FUNCTION    OF    LIVER.  349 

sugar  had  been  completely  washed  away  by  injecting      stream  of 

water  through  its  1.1 L-vessels,  will  be  found,  after  the  lapse  of 

r  few  hours,  to  contain  Bugar  in  abundance.  This  \ 
production  of  sugar  w;is  a  fact  which  could  only  !>■'  explained  in 
the  supposition  that  the  liver  contained  a  Bubstance,  readily  con- 
vertible into  sugar  in  the  course  merely  of  post-mortem  decom- 
position :  and  this  theory  was  proved  correct  by  the  3  ry  of  a 
substance  in  the  liver  allied  to  starch,  and  now  generally  termed 
glycogen.  We  may  believe,  therefore,  that  the  liver  does  ii"t  form 
Bugar  directly  from  the  materials  brought  to  it  by  the  blood,  but 
that  glycogen  is  first  formed  and  stored  in  its  substance:  and 
that  the  sugar,  when  present,  is  the  result  of  the  transformation 
of  the  latter. 

Quantity  of  Glycogen  formed. — Although,  as  before  mentioned,  glycogen 
is  produce  I  by  the  liverwheu  neither  starch  nor  sugar  is  present  in  the  E 

it>  amount  is  much  less  under  such  a  diet. 

.  1  rerage  amount  of  Glycogen  in  the  Um-  of  Dogs  under  various  Diets  (Pavy). 

Diet.  Amount  of  Glycogen  in  Liver. 

Animal  food 7-19  per  cent. 

Animal  food  with  sugar  (al»out  \  lb.  of  sugar  daily)     145         ,. 
v  getable  diet  (potatoes,  with  bread  or  barley-meal]     1723 

The  dependence  of  the  formation  of  glycogen  on  the  food  taken  is  also 
well  shown  by  the  following  results,  obtained  by  the  same  experimenter  : — 

J  verage  quantity  of  Glycogen  found  hi  the  Liter  of  Rabbits  after  Fasting 
anil  after  a  <■     t       Starch  ami  Sugar  respectively. 

Average  amount  of  Glycogen  in  I. 
After  fasting  for  three  days       ....     Practically  absent. 
.,     diet  of  starch  and  grape-sugar          .         .154  j>er  cent. 
..     cane-sugar 16-9 

Regarding  these  facts  there  is  no  dispute.  All  are  agreed  that 
glycogen  is  formed,  and  laid  up  in  store,  temporarily,  by  the  liver- 
cells  ;  and  that  it  is  not  formed  exclusively  from  saccharine  and 
amylaceous  foods,  but  from  albuminous  substances  also;  the 
albumen,  in  the  latter  case,  being  probably  split  up  into  glycogen, 
which  is  temporarily  stored  in  the  liver,  and  urea,  which  is  ex- 
creted by  the  kidney-. 

Destination  of  Glycogen. — There  are  two  chief  theories  on 


350  DIGESTION.  [chap.  viii. 

the  subject  of  the  destination  of  glycogen,  (i.)  That  the  conver- 
sion of  glycogen  into  sugar  takes  place  rapidly  during  life  by  the 
agency  of  a  ferment  also  formed  in  the  liver  :  and  the  sugar  is 
conveyed  away  by  the  blood  of  the  hepatic  veins,  and  soon  under- 
goes combustion.  (2.)  That  the  conversion  into  sugar  only 
occurs  after  death,  and  that  during  life  no  sugar  exists  in 
healthy  livers ;  glycogen  not  undergoing  this  transformation. 
The  chief  arguments  advanced  in  support  of  this  view  are,  (a) 
that  scarcely  a  trace  of  sugar  is  found  in  blood  drawn  during 
life  from  the  right  ventricle,  or  in  blood  collected  from  the  right 
side  of  the  heart  immediately  after  an  animal  has  been  killed  ; 
while  if  the  examination  be  delayed  for  a  very  short  time  after 
death,  sugar  in  abundance  ma}'  be  found  in  such  blood  ;  (b),  that 
the  liver,  like  the  venous  blood  in  the  heart,  is,  at  the  moment  of 
death,  completely  free  from  sugar,  although  afterwards  its  tissue 
speedily  becomes  saccharine,  unless  the  formation  of  sugar  be  pre- 
vented by  freezing,  boiling,  or  other  means  calculated  to  interfere 
with  the  action  of  a  ferment  on  the  amyloid  substance  of  the 
organ.  Instead  of  adopting  Bernard's  view,  that  normally,  during 
life,  glycogen  passes  as  sugar  into  the  hepatic  venous  blood,  and 
thereby  is  conveyed  to  the  lungs  to  be  further  disposed  of,  Pavy 
inclines  to  the  belief  that  it  may  represent  an  intermediate  stage  in 
the  formation  of  fat  from  materials  absorbed  from  the  alimentary 
canal. 

Liver-sugar  and  Glycogen. — To  demonstrate  the  presence 
of  sugar  in  the  liver,  a  portion  of  this  organ,  after  being  cut  into 
small  pieces,  is  bruised  in  a  mortar  to  a  pulp  with  a  small  quantity 
of  water,  and  the  pulp  is  boiled  with  sodium-sulphate  in  order  to 
precipitate  albuminous  and  colouring  matters.  The  decoction  is 
then  filtered  and  may  be  tested  for  glucose  (p.  284). 

Glycogen  (c6  hio  o5)  is  an  amorphous,  starch-like  substance, 
odourless  and  tasteless,  soluble  in  water,  insoluble  in  alcohol.  It 
is  converted  into  glucose  by  boiling  with  dilute  acids,  or  by  con- 
tact with  any  animal  ferment.  It  may  be  obtained  by  taking  a 
portion  of  liver  from  a  recently  killed  rabbit,  and,  after  cutting  it 
into  small  pieces,  placing  it  for  a  short  time  in  boiling  water.  It 
is  then  bruised  in  a  mortar,  until  it  forms  a  pulpy  mass,  and 
subsequently  boiled  in  distilled  water  for  about  a  quarter  of  an 
hour.     The  glycogen  is  precipitated  from  the  filtered  decoction  by 


i  hap.  vin.]  <.i.y i:.\. 

the  addition  of  alcohol.     Glycogen  has  been  found  in  many  other 
:h;ui  the  liver.      Si     Appendix,  | 

Glycosuria. — The  facility  with  which  the  glycogen  of  the  liver 
is  transformed  into  sugar  would  lead  to  the  expectation  that  this 
chemical  change,  under  many  circumstances,  would  occur  (  i  such 
an  extent  that  sugar  would  be  present  not  only  in  the  hepal 
veins,  but  in  the  blood  generally,  Such  is  frequently  the 
the  sugar  when  in  excess  in  the  blood  being  secreted  by  the 
kidneys,  and  thus  appearing  in  variable  quantities  in  the  urine 
(( rlycosuria). 

Influence  of  the  Nervous  System  in  producing  Glyco- 
suria.— Glycosuria  may  be  experimentally  produced  by  puncture 
of  the  medulla  oblongata  in  the  region  of  the  vaso-motor  centre. 
The  better  fed  the  animal  the  larger  is  the  amount  of  sugar  found 
in  the  urine  ;  whereas  in  the  case  of  a  starving  animal  no  sugar 
appears.  It  is,  therefore,  highly  probable  that  the  sugar  comes 
from  the  hepatic  glycogen,  since  in  the  one  case  glycogen  is  in 
excess,  and  in  the  other  it  is  almost  absent.  The  nature  of  the 
influence  is  uncertain.  It  may  be  exercised  in  dilating  the  hepatic 
vessels,  or  possibly  on  the  liver  cells  themselves.  The  whole 
course  of  the  nervous  stimulus  cannot  be  traced  to  the  liver,  but 
at  first  it  passes  from  the  medulla  down  the  spinal  cord  as  far  as 
— in  rabbits — the  fourth  dorsal  vertebra,  and  thence  to  the  1 
thoracic  ganglion. 

Many  other  circumstances  will  cause  glycosuria.  1:  has  been 
observed  after  the  administration  of  various  drugs,  after  the  in- 
jection of  urari,  poisoning  with  carbonic  oxide  gas,  the  inhalation 
pf  ether,  chloroform,  etc.,  the  injection  of  oxygenated  bl< 
into  the  portal  venous  system.  It  has  been  observed  in  man  after 
injuries  to  the  head,  and  in  the  course  of  various  disease  3. 

The    well-known  disease,   diabetus   m  in    which    a    large 

quantity  of  sugar  is  persistently  secreted   daily  with    the    urine, 
has.    doubtless,    -  Ioe      relation    to    the    normal    glycogenic 

function  of  the  liver;  but   the  nature  of  the  relationship   is   at 
present  quite  unknown. 

The  Intestinal  Secretion,  or  Suecus  Entericus. — On 
account  of  the  difficulty  in  isolating  the  secretion  of  the  glands 
in  the  wall  of  the  intestine  (Brunner's  and  Lieberkuhn's)  from 
other  secretions  poured   into  the  canal  (gastric  juice,   bile,   and 


352  DIGESTION.  [cHAr.  yiil 

pancreatic  secretion),  but  little  is  known  regarding  the  composi- 
tion of  the  former  fluid  (intestinal  jnice,  succus  entericus). 

It  is  said  to  be  a  yellowish  alkaline  fluid  with  a  specific  gravity 
of  ion,  and  to  contain  about  2*5  per  cent,  of  solid  matters 
(Thiry). 

Functions. — The  secretion  of  Brnnner's  glands  is  said  to  be  able 
to  convert  proteids  into  peptones,  and  that  of  Lieberkiihn's  is  be- 
lieved to  convert  starch  into  sugar.  To  these  functions  of  the 
succus  entericus  the  powers  of  converting  cane  into  grape  sugar, 
and  of  turning  cane  sugar  into  lactic,  and  afterwards  into  butyric 
acid,  are  added  by  some  physiologists.  It  also  probably  contains 
a  milk-curdling  ferment  (W.  Roberts). 

The  reaction  which  represents  the  conversion  of  cane  sugar  into, 
grape  sugar  may  be  represented  thus  : — 

2  G12  H22  01X       +       2  H2  0       =       C12  H2t  012       +       C13  H24  012 

Saccharose  Water  Dextrose  Lfevulose 

The  conversion  is  probably  effected  by  means  of  a  hydrolytic 
ferment.     (Inversive  ferment,  Bernard.) 

The  length  and  complexity  of  the  digestive  tract  seem  to  be  closely  con- 
nected with  the  character  of  the  food  on  which  an  animal  lives.  Thus,  in 
all  carnivorous  animals,  such  as  the  cat  and  dog,  and  pre-eminently  in  car- 
nivorous birds,  as  hawks  and  herons,  it  is  exceedingly  short.  The  seals, 
which,  though  carnivorous,  possess  a  very  long  intestine,  appear  to  furnish 
an  exception  ;  but  this  is  doubtless  to  be  explained  as  an  adaptation  to 
their  aquatic  habits  :  their  constant  exposure  to  cold  requiring  that  they 
should  absorb  as  much  as  possible  from  their  intestines. 

Herbivorous  animals,  on  the  other  hand,  and  the  ruminants  especially. 
have  very  long  intestines  (in  the  sheep  30  times  the  length  of  the  body)- 
which  is  no  doxibt  to  be  connected  with  their  lowly  nutritious  diet.  In, 
others,  such  as  the  rabbit,  though  the  intestines  are  not  excessively  long, 
this  is  compensated  by  the  great  length  and  capacity  of  the  caecum.  In 
man.  the  length  of  the  intestines  is  intermediate  between  the  extremes  of 
the  carnivora  and  herbivora.  and  his  diet  also  is  intermediate. 


Summary  of  the    Digestive    Changes  in  the  Small 

Intestine. 

In  order  to  understand  the  changes  in  the  food  which  occur 
during  its  passage  through  the  small  intestine,  it  will  be  well  to 
refer  briefly  to  the  state  in  which  it  leaves  the  stomach  through 
the  pylorus.  It  has  been  said  before,  that  the  chief  office  of  the 
stomach  is  not  only  to  mix  into  an  uniform  mass  all  the  varieties 


<  hap.  vin.]  stmmakv    OF    DIGESTION.  353 

of  food  that  reach  it  through  the  oesophagus,  but  especially  t<» 
dissolve  the  nitrogenous  portion  by  means  of  the  gastric  juice. 
The  fatty  matters,  during  their  sojourn  in  the  stomach,  become 
more  thoroughly  mingled  with  the  other  constituents  of  the   food 

taken,  but  are  not  yet  in  a  state  fit  for  absorption.  The  con- 
version of  starch  into  sugar,  which  began  in  the  mouth,  lias 
been  interfered  with,  if  not  altogether  stopped.  The  soluble 
matters — both  those  which  were  so  from  the  first,  as  sugar  and 

saline  matter,  and  the  gastric  peptones — have  begun  to  dis- 
appear by  absorption  into  the  blood-vessels,  and  the  same  thing 
has  befallen  such  fluids  as  may  have  been  swallowed, — wine, 
water,  etc. 

The  thin  pultaceous  chyme,  therefore,  which  during  the  whole 
period  of  gastric  digestion,  is  being  constantly  squeezed  or  strained 
through  the  pyloric  orifice  into  the  duodenum,  consists  of  albu- 
minous matter,  broken  down,  dissolving  and  half  dissolved;  fatty 
matter  broken  down  and  melted,  but  not  dissolved  at  all;  starch 
very  slowly  in  process  of  conversion  into  sugar,  and  as  it  becomes 
sugar,  also  dissolving  in  the  fluids  with  which  it  is  mixed  ;  while, 
with  these  are  mingled  gastric  fluid,  and  fluid  that  has  been 
swallowed,  together  with  such  portions  of  the  food  as  are  not 
digestible,  and  will  be  finally  expelled  as  part  of  the  faeces. 

On  the  entrance  of  the  chyme  into  the  duodenum,  it  is  sub- 
jected to  the  influence  of  the  bile  and  pancreatic  juice,  which  are 
then  poured  out,  and  also  to  that  of  the  succus  entericus.  All 
these  secretions  have  a  more  or  less  alkaline  reaction,  and  hy  their 
.id mixture  with  the  gastric  chyme,  its  acidity  becomes  less  and 
less  until  at  length,  at  about  the  middle  of  the  small  intestine, 
the  reaction  becomes  alkaline  and  continues  so  as  far  as  the  ileo- 
cecal valve. 

The  special  digestive  functions  of  the  small  intestine  may  be 
taken  in  the  following  order  : — 

(i.)  One  important  duty  of  the  small  intestine  is  the  alteration 
of  the  fat  in  such  a  manner  as  to  make  it  fit  for  absorption ;  and 
there  is  no  doubt  that  this  change  is  chiefly  effected  in  the  upper 
part  of  the  small  intestine.  What  is  the  exact  share  of  the  pro- 
cess, however,  allotted  respectively  to  the  bile,  to  the  pancreatic 
secretion,  and  to  the  intestinal  juice,  is  still  uncertain, — probably 
the  pancreatic  juice  is  the  most  important.     The  fat  is  changed 

A    A 


354  DIGESTION.  [chap.  vin. 

in  two  ways.  (a).  To  a  slight  extent  it  is  chemically  decomposed 
by  the  alkaline  secretions  with  which  it  is  mingled,  and  a  soap  is 
the  result.  (6).  It  is  emulsionised,  i.e.,  its  particles  are  minutely 
subdivided  and  diffused,  so  that  the  mixture  assumes  the  condition 
of  a  milky  fluid,  or  emulsion.  As  will  be  seen  in  the  next 
Chapter,  most  of  the  fat  is  absorbed  by  the  lacteals  of  the  intes- 
tine, but  a  small  part,  which  is  saponified,  is  also  absorbed  by  the 
blood-vessels. 

(2.)  The  albuminous  substances  which  have  been  partly  dis- 
solved in  the  stomach,  and  have  not  been  absorbed,  are  subjected 
to  the  action  of  the  pancreatic  and  intestinal  secretions.  The  pepsin 
is  rendered  inert  by  being  precipitated  together  writh  the  gastric 
peptones  and  parapeptones,  as  soon  as  the  chyme  meets  with  bile. 
By  these  means  the  pancreatic  ferment  trypsin  is  enabled  to  pro- 
ceed with  the  further  conversion  of  the  parapeptones  into  peptones,, 
and  of  part  of  the  peptones  (hemipeptone,  Kiihne)  into  leucin 
and  ty rosin.  Albuminous  substances,  which  are  chemically  altered 
in  the  process  of  digestion  (peptones),  and  gelatinous  matters 
similarly  changed,  are  absorbed  by  both  the  blood-vessels  and 
lymphatics  of  the  intestinal  mucous  membrane.  Albuminous 
matters,  in  a  state  of  solution,  which  have  not  undergone  the 
peptonic  change,  are  probably,  from  the  difficulty  with  which  they 
diffuse,  absorbed,  if  at  all,  almost  solely  by  the  lymphatics. 

(3.)  The  starchy,  or  amyloid  portions  of  the  food,  the  conver- 
sion of  which  into  dextrin  and  sugar  was  more  or  less  interrupted 
during  its  stay  in  the  stomach,  is  now  acted  on  briskly  by  the 
pancreatic  juice  and  the  succus  entericus ;  and  the  sugar,  as  it  is 
formed,  is  dissolved  in  the  intestinal  fluids,  and  is  absorbed  chiefly 
by  the  blood-vessels. 

(4.)  Saline  and  saccharine  matters,  as  common  salt,  or  cane 
sugar,  if  not  in  a  state  of  solution  beforehand  in  the  saliva  or 
other  fluids  which  may  have  been  swallowed  with  them,  are  at 
once  dissolved  in  the  stomach,  and  if  not  here  absorbed,  are  soon 
taken  up  in  the  small  intestine  ;  the  blood-vessels,  as  in  the  last 
case,  being  chiefly  concerned  in  the  absorption.  Cane  sugar  is  in 
part  or  wholly  converted  into  grape-sugar  before  its  absorption. 
This  is  accomplished  partially  in  the  stomach,  but  also  by  a 
ferment  in  the  succus  entericus. 

(5.)  The   liquids,  including  in  this  term  the  ordinary  drinks. 


chap,  vin.]  8UMMABY    OF    DIGE8TION.  355 

rater,  wine,  ale,  0.,  which  mayhavi  rption 

in   the   Btomach,    are    absorbed    probably   r<  their 

entrance  into  the  intestine  ;  the  fluidity  of  the  contents  of  the 
latter  being  preserved  more  by  the  constant  secretion  of  fluid  I 
the   intestinal   glands,   pancreas,  and    liver,  than   by  any  given 
portion   of  fluid,  whether  swallowed  or  secreted,  remaining  l<-ng 
unabsorbed.     From  this  fact,  th.  it  may  be  gathered  that 

there  is  a  kind  of  circulation  constantly  proceeding  from  th< 
intestines  into  the  blood,  and  from  the  blood  into  the  intestines 
again  ;  for  as  all  the  fluid — a  very  large  amount — secreted  by 
the  intestinal  glands,  must  come  from  the  blood,  the  latter  would 
be  too  much  drained,  were  it  not  that  the  same  fluid  after  .secre- 
tion is  again  re-absorbed  into  the  current  of  blood — going  into 
the  blood  charged  with  nutrient  products  of  digestion — coming 
out  again  by  secretion  through  the  glands  in  a  comparatively 
uncharged  condition. 

At  the  lower  end  of  the  small  intestine,  the  chyme,  still  thin 
and  pultaceous,  is  of  a  light  yellow  colour,  and  has  a  distinctly 
fecal  odour.  This  odour  depends  upon  the  formation  of  indol. 
In  this  state  it  passes  through  the  ileo-caecal  opening  into  the 
large  intestine. 

Summary  of  the  Digestive  Changes  in  the  Large 

Intestine. 
The  changes  which  take  place  in  the   chyme  in  the  large  in- 
line are  probably  only  the  continuation  of  the  same   changes 
that  occur  in  the  course  of  the  food'-       a£  ige  through  the  upper 
part  of  the  intestinal  canal.      From  the  absence  of  villi,  however, 
we    may    conclude    that    absorption,    especially    of   fatty    matter, 
in   great   part   completed   in   the   small   intestine  ;  while,   from 
the  still  half-liquid,  pultaceous  eonsistence  of  the  chyme  when  it 
first  enters  the  caecum,  there  can  be  no  doubt  that  the  absorp- 
tion of  liquid  is    not    by  any  means    concluded.      The    peculiar 
odour,   moreover,    which  is    acquired  after  a   short    time  by  the 
contents   >>t'  the   Luge   bowel,   would   seem  to  indicate  a   further 
chemical  change  in  the  alimentary  matters  or  in  the  digestive 
fluids,   or   both.      The    acid   reaction,    which   had  disappeared  in 
the   .-mall  bowel,  again   becomes  very  manifest   in  the    caecum — 
probably  from  acid  fermentation-processes  in  ><-meof  the  materials 
the  food. 

A    A    2 


35^ 


DIGESTION. 


[CHAP.  VIII. 


There  seems  no  reason  to  conclude  that  any  special  *  secon- 
dary digestive'  process  occurs  in  the  caecum  or  in  any  other 
part  of  the  large  intestine.  Probably  any  constituent  of  the  food 
which  has  escaped  digestion  and  absorption  in  the  small  bowel 
may  be  digested  in  the  large  intestine;  and  the  power  of  this 
part  of  the  intestinal  canal  to  digest  fatty,  albuminous,  or  other 
matters,  may  be  gathered  from  the  good  effects  of  nutrient 
enemata,  so  frequently  given  when  from  any  cause  there  is 
difficulty  in  introducing  food  into  the  stomach.  In  ordinary 
healthy  digestion,  however,  the  changes  which  ensue  in  the 
chyme  after  its  passage  into  the  large  intestine,  are  mainly  the 
absorption  of  the  more  liquid  parts,  and  the  completion  of  the 
changes  which  were  proceeding  in  the  small  intestine, — the 
process  being  assisted  by  the  secretion  of  the  numerous  tubular 
glands  therein  present. 

Fgeces. — By  these  means  the  contents  of  the  large  intestine,  as 
they  proceed  towards  the  rectum,  become  more  and  more  solid,  and 
losing  their  more  liquid  and  nutrient  parts,  gradually  acquire  the 
odour  and  consistence  characteristic  of  faxes.  After  a  sojourn  of 
uncertain  duration  in  the  sigmoid  flexure  of  the  colon,  or  in  the 
rectum,  they  are  finally  expelled  by  the  act  of  defaecation. 

The  average  quantity  of  solid  faecal  matter  evacuated  by  the 
human  adult  in  twenty-four  hours  is  about  six  or  eight  ounces. 


Composition  of  Faeces. 

Water 733"°o 

.Solids 267-00 

Special  excrementitious  constituents  : — Excretin.  excre-  x 
toleic  acid  (Marcet),  and  stercorin  (Austin  Flint). 

Salts  : — Chiefly  phosphate  of  magnesium  and  phosphate 
of  calcium,  with  small  quantities  of  iron,  soda.  lime, 
and  silica. 

Insoluble  residue  of  the  food  (chiefly  starch  grains,  woody- 
tissue,  particles  of  cartilage  and  fibrous  tissue,  un-         267-00 
digested  muscular  fibres   or  fat,  and  the  like,  with 
insoluble   substances  accidentally  introduced  with 
the  food. 

Mucus,  epithelium,  altered  colouring  matter  of  bile,  fatty 
acids,  etc. 

Varying  quantities  of  other  constituents  of  bile,  and  de- 
rivatives from  them. 


chap,  viii.]  DEFECATION.  357 

Length  of  Intestinal  Digestive  Period. — The  time  occu- 
pied by  the  journey  of  a  given  portion  of  food  from  the  Btomach 

bo   the    anus,   varies    considerably  even    in  health,  and  on   this 
account,   probably,   it   is  that  such  different   opinions  have  been 
expressed   in   regard  to   the   subject.      About   twelve   hours   ari 
occupied   by  the  journey  of  an  ordinary  meal  through  the  small 
intestine,    and    twenty-four   to    thirty-six    hours   by    the    pass;. 
through  the  large  bowel.     (Brinton.) 

Defsecation. —  Immediately  before  the  act  of  voluntary  expul- 
sion of  faeces  (defalcation)  there  is  usually,  first  an  inspiration,  as 
in  the  case  of  coughing,  sneezing,  and  vomiting;  the  glottis  is  then 
closed,  and  the  diaphragm  fixed.  The  abdominal  muscles  are  con- 
tracted as  in  expiration  ;  but  as  the  glottis  is  closed,  the  whole  of 
their  pressure  is  exercised  on  the  abdominal  contents.  The 
sphincter  of  the  rectum  being  relaxed,  the  evacuation  of  its  con- 
tents takes  place  accordingly  ;  the  effect  being,  of  course,  increased 
by  the  peristaltic  action  of  the  intestine.  As  in  the  other  actions 
just  referred  to,  there  is  as  much  tendency  to  the  escape  of  the 
contents  of  the  lungs  or  stomach  as  of  the  rectum ;  but  the  pres- 
sure is  relieved  only  at  the  orifice,  the  sphincter  of  which  instinc- 
tively or  involuntarily  yields  (see  fig.  144). 

Nervous  Mechanism  of  Defsecation. — The  anal  sphincter 
muscle  is  normally  in  a  state  of  tonic  contraction.  The  nervous 
centre  which  governs  this  contraction  is  probably  situated  in  the 
lumbar  region  of  the  spinal  cord,  inasmuch  as  in  cases  of  division 
of  the  cord  above  this  region  the  sphincter  regains,  after  a  time,  to 
some  extent  the  tonicity  which  is  lost  immediately  after  the  opera- 
tion. By  an  effort  of  the  will,  acting  through  the  centre,  the  con- 
traction may  be  relaxed  or  increased.  In  ordinary  cases  the 
apparatus  is  set  in  action  by  the  gradual  accumulation  of  faaces  in 
the  sigmoid  flexure  and  rectum  pressing  against  the  sphincter  and 
causing  its  relaxation;  this  sensory  impulse  acting  through  the 
brain  and  reflexly  through  the  spinal  centre.  Peristaltic  action, 
especially  of  the  sigmoid  flexure  in  pressing  onwards  the  fax-es 
against  the  sphincter,  is  a  very  important  part  of  the  act. 

The  Gases  contained  in  the  Stomach  and  Intestines. — 
Under  ordinary  circumstances,  the  alimentary  canal  contains  a 
considerable  quantity  of  gaseous  matter.     Any  one  who  has  had 


353 


DIGESTION. 


[CHAP.  VIII. 


occasion,  in  a  post-mortem  examination,  either  to  lay  open  the 
intestines,  or  to  let  out  the  gas  which  they  contain,  must  have 
been  struck  by  the  small  space  afterwards  occupied  by  the  bowels, 
and  by  the  large  degree,  therefore,  in  which  the  gas,  which 
naturally  distends  them,  contributes  to  fill  the  cavity  of  the 
abdomen.  Indeed,  the  presence  of  air  in  the  intestines  is  so 
constant,  and,  within  certain  limits,  the  amount  in  health  so 
uniform,  that  there  can  be  no  doubt  that  its  existence  here  is  not 
a  mere  accident,  but  intended  to  serve  a  definite  and  important 
purpose,  although,  probably,  a  mechanical  one. 

Sources. — The  sources  of  the  gas  contained  in  the  stomach 
and  bowels  may  be  thus  enumerated  : — 

i.  Air  introduced  in  the  act  of  swallowing  either  food  or  saliva  ;  2.  Gases 
developed  by  the  decomposition  of  alimentary  matter  or  of  the  secretions 
and  excretions  mingled  with  it  in  the  stomach  and  intestines  ;  3.  It  is 
probable  that  a  certain  mutual  interchange  occurs  between  the  gases  con- 
tained in  the  alimentary  canal,  and  those  present  in  the  blood  of  these 
gastric  and  intestinal  blood-vessels  ;  but  the  conditions  of  the  exchange  are 
not  known,  and  it  is  very  doubtful  whether  anything  like  a  true  and  definite 
secretion  of  gas  from  the  blood  into  the  intestines  or  stomach  ever  takes 
place.  There  can  be  no  doubt,  however,  that  the  intestines  may  be  the 
proper  excretory  organs  for  many  odorous  and  other  substances,  either 
absorbed  from  the  air  taken  into  the  lungs  in  inspiration,  or  absorbed  in  the 
upper  part  of  the  alimentary  canal,  again  to  be  excreted  at  a  portion  of  the 
same  tract  lower  down — in  either  case  assuming  rapidly  a  gaseous  form  after 
their  excretion,  and  in  this  way.  perhaps,  obtaining  a  more  ready  egress  from 
the  body.  It  is  probable  that,  under  ordinary  circumstances,  the  gases  of 
the  stomach  and  intestines  are  derived  chiefly  from  the  second  of  the  sources 
which  have  been  enumerated  (Brinton). 


Composition  of  Gases  contained  in  trie  Alimentary  Canal. 

(Tabulated  from  various  authorities  by  Brixton.) 


Whence  obtained. 


Stomach    .     .     .     . 
Small  Intestines 
Csecum      .     .     .     . 

Colon 

Rectum     .     .     .     . 
Expelled  per  anvm 


Composition  by  Volume. 

Oxygen. 

Xitrog. 

Carbon. 
Acid. 

Hydrog. 

Carburet. 
Hydrogen. 

Sulphuret. 
Hydrogen,  j 

II 

71 

14 

4 

— 

— 

— 

32 

30 

3« 

— 

I 

-  trace. 

66 

35 

12 

57 

8 
6 

13 

8 

— 

46 

43 

— 

11 

22 

4i 

.9 

19 

i 

hap.  viii.]        MOVEMENTS    OF    THE    l.YJ  Kstixks.  3^ 

Movements  of  the  Intestines. —  It  remains  only  to  consider 
the  manner  in  which  the  food  and  the  several  secretions  mingled 
with  it  arc  moved  through  the  intestinal  canal,  so  as  to  be  slowly 
subjected  to  the  influence  of  fresh  portions  of  intestinal  secretion, 
and  as  slowly  exposed  to  the  absorbent  power  of  all  the  villi 
and  blood  vessels  of  the  mucous  membrane.  The  movement  of 
the  intestines  is  peristaltic  or  vermicular,  and  is  effected  by  the 
alternate  contractions  and  dilatations  of  successive  portions  of  the 
intestinal  coats.  The  contractions,  which  may  commence  at  any 
point  of  the  intestine,  extend  in  a  wave-like  manner  along  the 
tube.  In  any  given  portion,  the  longitudinal  muscular  fibres 
contract  first,  or  more  than  the  circular;  they  draw  a  portion  of 
the  intestine  upwards,  or,  as  it  were,  backwards,  over  the  sub- 
stance to  be  propelled,  and  then  the  circular  fibres  of  the  same 
portion  contracting  in  succession  from  above  downwards,  or,  as  it 
were,  from  behind  forwards,  press  on  the  substance  into  the 
portion  next  below,  in  which  at  once  the  same  succession  of  action 
next  ensues.  These  movements  take  place  slowly  and,  in 
health,  are  commonly  unperceived  by  the  mind  ;  but  they  are 
perceptible  when  they  are  accelerated  under  the  influence  of  any 
irritant. 

The  movements  of  the  intestines  are  sometimes  retrograde ;  and 
there  is  no  hindrance  to  the  backward  movement  of  the  contents 
of  the  small  intestine.  But  almost  complete  security  is  afforded 
against  the  passage  of  the  contents  of  the  large  into  the  small  in- 
testine by  the  ileo-crecal  valve.  Besides, — the  orifice  of  communi- 
cation between  the  ileum  and  caecum  (at  the  borders  of  which 
orifice  are  the  folds  of  mucous  membrane  which  form  the  valve)  is 
encircled  with  muscular  fibres,  the  contraction  of  which  prevents 
the  undue  dilatation  of  the  orifice. 

Proceeding  from  above  downwards,  the  muscular  fibres  of  the 
large  intestine  become,  on  the  whole,  stronger  in  direct  propor- 
tion to  the  greater  strength  required  for  the  onward  moving  of 
the  faces,  which  are  gradually  becoming  firmer.  The  greatest 
strength  is  in  the  rectum,  at  the  termination  of  which  the  circular 
unstriped  muscular  fibres  form  a  strong  band  called  the  internal 
sphincter  ;  while  an  external  sphincter  muscle  with  striped  fibres 
is  placed   rather  lower   down,   and   more  externally,    and   as    we 


360  DIGESTION.  [chap,  vnu 

have  seen  above,  holds  the  orifice  close  by  a  constant  slight  tonic 
contraction. 

Experimental  irritation  of  the  brain  or  cord  produces  no 
evident  or  constant  effect  on  the  movements  of  the  intestines, 
during  life ;  yet  in  consequence  of  certain  conditions  of  the  mind 
the  movements  are  accelerated  or  retarded;  and  in  paraplegia 
the  intestines  appear  after  a  time  much  weakened  in  their  power, 
and  costiveness,  with  a  tympanitic  condition,  ensues.  Immediately 
after  death,  irritation  of  both  the  sympathetic  and  pneumo-gastric 
nerves,  if  not  too  strong,  induces  genuine  peristaltic  movements 
of  the  intestines.  Violent  irritation  stops  the  movements.  These 
stimuli  act,  no  doubt,  not  directly  on  the  muscular  tissue  of  the 
intestine,  but  on  the  ganglionic  plexus  before  referred  to. 

Influence  of  the  Nervous  System  on  Intestinal  Digestion. 
— As  in  the  case  of  the  oesophagus  and  stomach,  the  peristaltic 
movements  of  the  intestines  are  directly  due  to  reflex  action 
through  the  ganglia  and  nerve  fibres  distributed  so  abundantly 
in  their  walls  (p.  315);  the  presence  of  chyme  acting  as  the 
stimulus,  and  few  or  no  movements  occurring  when  the  intes- 
tines are  empty.  The  intestines  are,  moreover,  connected  with 
the  higher  nerve-centres  by  the  splanchnic  nerves,  as  well  as 
other  branches  of  the  sympathetic  which  come  to  them  from 
the  coeliac  and  other  abdominal  plexuses. 

The  splanchnic  nerves  are  in  relation  to  the  intestinal  move- 
ments, inhibitory — these  movements  being  retarded  or  stopped 
when  the  splanclmics  are  irritated.  As  the  vasomotor  nerves  of 
the  intestines,  the  splanclmics  are  also  much  concerned  in  intes- 
tinal digestion. 


chap.ix.]  LYMPHATICS    AND    LACTEALS  -f,i 

CHAPTEE   IX. 

ABSORPTION. 

The  process  of  Absorption  has,  for  one  of  its  objects,  the  intro- 
duction into  the  blood  of  fresh  materials  from  the  food  and  air 
and  of  whatever  comes  into  contact  with  the  external  or  internal 
surfaces  of  the  body ;  and,  for  another,  the  gradual  removal  of 
parts  of  the  body  itself,  when  they  need  to  be  renewed.  In  both 
these  offices,  i.e.,  in  both  absorption  from  without  and  absorption 
from  within,  the  process  manifests  some  variety,  and  a  very  wide 
range  of  action  ;  and  in  both  two  sets  of  vessels  are,  or  may  be, 
concerned,  namely,  the  Blood-vessels,  and  the  Lymph-vessels  or 
Lymphatics  to  which  the  term  Absorbents  has  been  also  applied. 

The  Lymphatic  Vessels  and  Glands. 

Distribution. — The  principal  vessels  of  the  lymphatic  system 
are,  in  structure  and  general  appearance,  like  very  small  and  thin- 
walled  veins,  and  like  them  are  provided  with  valves.  By  one 
extremity  they  commence  by  fine  microscopic  branches,  the 
lymphatic  capillaries  or  lymph-capillaries,  in  the  organs  and  tissues 
of  the  body,  and  by  their  other  extremities  they  end  directly  or 
indirectly  in  two  trunks  which  open  into  the  large  veins  near  the 
heart  (fig.  206).  Their  contents,  the  lymph  and  chyle,  unlike  the 
blood,  pass  only  in  one  direction,  namely,  from  the  fine  branches 
to  the  trunk  and  so  to  the  large  veins,  on  entering  which  they  arc 
mingled  with  the  stream  of  blood,  and  form  part  of  its  consti- 
tuents. Remembering  the  course  of  the  fluid  in  the  lymphatic 
vessels,  viz.,  its  passage  in  the  direction  only  towards  the  large 
veins  in  the  neighbourhood  of  the  heart,  it  will  readily  be  seen 
from  fig.  206  that  the  greater  part  of  the  contents  of  the  lymphatic 
system  of  vessels  passes  through  a  comparatively  large  trunk 
called  the  thoracic  duct,  which  finally  empties  its  contents  into  the 
blood-stream,  at  the  junction  of  the  internal  jugular  and  sub- 
clavian veins  of  the  left  side.  There  is  a  smaller  duct  on  the 
right  side.     The  lymphatic   vessels  of  the  intestinal    canal    arc 


362 


ABSORPTION. 


[chap.  IX. 


called  lacteal*,  because,  during  digestion,   the  fluid   contained  in 
them  resembles  milk  in  appearance;  and  the  lymph  in  the  lacteals 


Lymphatics    of    head 
and  neck,  right. 

Eight  internal  jugular 

vein. 

Right  subclavian  vein. 

Lymphatics    of    right 
arm. 


Eeceptaculum  chyli. 


Lymphatics    of    lower 
extremities. 


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Lymphatics    of    head 
and  neck,  left. 

Thoracic  duct. 

Left  subclavian  vein. 


Thoracic  duct. 


Lacteals. 


Lymphatics   of   lower 
extremities. 


Fig.  206.— Diagram  of  the  principal  groups  of  lymphatic  vessels  (from  Quain). 


during  the  period  of  digestion  is  called  chyle.  There  is  no  essen- 
tial distinction,  however,  between  lacteals  and  lymphatics.  Iu  some 
parts  of  their  course  all  lymphatic  vessels  pass  through  certain 
bodies  called  lymphatic  glands. 

Lymphatic  vessels  are  distributed  in  nearly  all  parts  of  the  body. 
Their  existence,  however,  has  not  yet  been  determined  in  the 
placenta,  the  umbilical  cord,  the  membranes  of  the  ovum,  or 
in  any  of  the  non-vascular  parts,  as  the  nails,  cuticle,  hair  and 
the  like. 


•   HAP.    IX.  | 


ORIGIN    OF    LYMPH    CAPILLAEIES. 


03 


Origin  of  Lymph  Capillaries.  -The  lymphatic  capillariet 
commence  most  commonly  either  in  closely-meshed  networks,  or 
m  irregular  lacunar  spaces  between  the  various  structur< 
which  the  different  organs  are  composed.  Such  irregular  spaces, 
forming  what  is  now  termed  the  lymph-canalicular  system,  have 
been  shown  to  exist  in  many  tissues.      In  serous  membranes  such 


Fig.  207.— Lymphatics  of  central  tendon  of  rabbit's  diaphragm,  stained  with  silver  nitrate 
The  ground  substance  has  been  shaded  diagrammatic-ally  to  bring  out  the  lympha- 
tics clearly.  I.  Lymphatics  lined  by  long  narrow  endothelial  cells,  and  showing  v 
valves  at  frequent  intervals  (Schofield) .  °    ' 

as  the  omentum  and  mesentery  they  occur  as  a  connected  system 
of  very  irregular  branched  spaces  partly  occupied  by  connective 
tissue-corpuscles,  and  both  in  these  and  in  many  other  tissues  arc 
found  to  communicate  freely  with  regular  lymphatic  vessels.  In 
many  eases,  though  they  are  formed  mostly  by  the  chinks  and 
crannies  between  the  blood-vessels,  secreting  ducts,  and  other 
parts  which  may  happen  to  form  the  framework  of  the  organ 
in  which  they  exist,  they  are  lined  by  a  distinct  layer  of  endo- 
thelium. 

The  lacteals  offer   an  illustration  of  another   mode    of  origin 
namely,  in  blind  dilated  extremities  (figs.  192  and  193);   but  there 
is  no  essential  difference    in    structure    between   these  and    the 
lymphatic  capillaries  of  other  parts. 


;64 


ABSORPTION, 


[CHAP.  IX. 


Structure  of  Lymph  Capillaries. — The  structure  of  lym- 
phatic capillaries  is  very  similar  to  that  of  blood-capillaries  :  their 
walls  consist  of  a  single  layer  of  endothelial  cells  of  an  elongated 


Fig.  208. — Lymphatic  v of    the    head    and  neck   and    the    upper    port  of  the  trunk 

(Mascagm).  &■ — The  chest  and  pericardium  have  been  opened  on  the  left  side,  and 
the  left  mamma  detached  and  thrown  outwards  over  the  left  arm,  so  as  to  expose  a 
great  part  of  its  deep  surface.  The  principal  lymphatic  vessels  and  glands  are  shown 
on  the  side  of  the  head  and  face,  and  in  the  neck,  axilla,  and  mediastinum.  Between 
the  left  internal  jugular  vein  and  the  common  carotid  artery,  the  upper  ascending 
part  of  the  thoracic  duct  marked  1,  and  above  this,  and  descending  to  2,  the  arch  and 
last  part  of  the  duct.  The  termination  of  the  upper  lymphatics  of  the  diaphragm 
in  the  mediastinal  glands,  as  well  as  the  cardiac  and  the  deep  mammary  lymphatics, 
is  also  shown. 


form  and  sinuous  outline,  which  cohere  along  their  edges  to  form 
a  delicate  membrane.  They  differ  from  blood  capillaries  mainly 
in  their  larger  and  very  variable  calibre,  and  in  their  numerous 
communications  with  the  spaces  of  the  lymph-canalicular  system. 

Communications  of  the  Lymphatics. — The  fluid   part  of 
the  blood   constantly  exudes  or  is  strained   through  the  walls  of 


hap.  ix.]         STEUCTUEE    OP    LTMPfl    CAPILLAEIES. 


3^5 


the  blood-capillaries,  so  as  to  u  rarrounding 

and  occupies  the  interspaces   which  exist  among  their  different 


:   »/  the  ha    '.         z-  Two  small 
glands  at  the  bend,  of  the  arm.    6.  Radial  lymphatic  vessels.     7.  Ulnar  lymphatic 
Palmar  arch  of  lymphatics.     9,  9'.    Outer  and  inner   - 
1  t^phalic  vein.     ■'..  Eadial  vein.     e.  Median  vein.    /'.  Ulnar  vein.     The  lymp':. 
are  represented  as  lying  on  the  deep  :   b  Mascagni.) 

Fig.  210. — Sup€  ncial  lymphatics  of  right  groin  and  upper  part  of  thigh,  ±.     I.  Upper  inguinal 
glands.     2.  2'.  Lower  inguin-.il  or  femoral  glands.    5,  3'.  Plexus  of  lymphatics  in  the 
:rse  of  the  long  saphenous  vein.      Mu    ..mi.) 

elements.    These  same  interspaces  have  been  shown,  as  just  stated, 

i-m  the  beginnings  of  the  lymph-capillaries  ;  and  the  latter, 

therefore,  are  the  means  of  collecting  the  exuded  blood  plasma, 


-66  ABSORPTION.  [chap.  ix. 

and  returning  that  part  which  is  not  directly  absorbed  by  the 
tissues  into  the  blood-stream.  For  many  years,  the  notion  of 
the  existence  of  any  such  channels  between  the  blood  -  vessels 
and  lymph-vessels  as  would  admit  blood-corpuscles,  has  been 
given  up  ;  observations  having  proved  that,  for  the  passage  of 
such  corpuscles,  it  is  not  necessary  to  assume  the  presence  of 
any  special  channels  at  all,  inasmuch  as  blood-corpuscles  can 
pass  bodily,  without  much  difficulty,  through  the  walls  of  the 
blood-capillaries  and  small  veins  (p.  199),  and  could  pass  with 
still  less  trouble,  probably,  through  the  comparatively  ill-defined 
walls  of  the  capillaries  which  contain  lymph. 

It  is  worthy  of  note  that,  in  many  animals,  both  arteries  and  veins,  espe- 
cially the  latter,  are  often  found  to  be  more  or  less  completely  ensheathed 
in  large  lymphatic  channels.  In  turtles,  crocodiles,  and  many  other 
animals,  the  abdominal  aorta  is  enclosed  in  a  large  lymphatic  vessel. 

Stomata. — In  certain  parts  of  the  body  openings  exist  by  which 
lymphatic  capillaries  directly  communicate  with  parts  hitherto  sup- 
posed to  be  closed  cavities.  If  the  peritoneal  cavity  be  injected 
with  milk,  an  injection  is  obtained  of  the  plexus  of  lymphatic  vessels 
of  the  central  tendon  of  the  diaphragm  (fig.  207) ;  and  on  remov- 
ing a  small  portion  of  the  central  tendon,  with  its  peritoneal 
surface  uninjured,  and  examining  the  process  of  absorption  under 
the  microscope,  the  milk-globules  run  towards  small  natural 
openings  or  stomata  between  the  epithelial  cells,  and  disappear  by 
passing  vortex-like  through  them.  The  stomata,  which  have  a 
roundish  outline,  are  only  wide  enough  to  admit  two  or  three  milk- 
globules  abreast,  and  never  exceed  the  size  of  an  epithelial  cell. 

Pseudostomata. — When  absorption  into  the  lymphatic  system 
takes  place  in  membranes  covered  by  epithelium  or  endothelium 
through  the  interstitial  or  intercellular  cement-substauce,  it  is 
said  to  take  place  through  pseudostomata. 

Demonstration  of  Lyvqrfiatic*  if  Diaphragm. — The  stomata  on  the  peri- 
toneal surface  of  the  diaphragm  are  the  openings  of  -hort  vertical  canals 
which  lead  up  into  the  lymphatics,  and  are  lined  by  cells  like  those  of 
germinating  endothelium  (p.  27).  By  introducing  a  solution  of  Berlin 
blue  into  the  peritoneal  cavity  of  an  animal  shortly  after  death,  and  sus- 
pending it.  head  downwards,  an  injection  of  the  lymphatic  vessels  of  the 
diaphragm,  through  the  stomata  on  its  peritoneal  surface,  may  readily  be 
obtained,  if  artificial  respiration  be  carried  on  for  about  half  an  hour.  In 
this  wav  it  has  been  found  that  in  the  rabbit  the  Lymphatics  are  arranged 


LP.  ix. |  STOMATA    AND      PSEUDOSTOMATA.  367 

between  the  tendon  bundles  of  the  centrum  tendineum ;  and  they  are 
hence  termed  interfascicular.  The  centrum  tendineum  Is  coated  by  endo- 
thelium on  its  pleural  and  peritoneal  surfaces,  and  its  substance  consif 


Fig.  211. — Peritoneal  surface  of  septum  eisterna  lymphatica  magna  of  frog.  The  stomata, 
some  of  which  are  open,  some  collapsed,  are  surrounded  by  germinating  endothelium. 
X  160.    (Klein. 

tendon  bundles  arranged  in  concentric  rings  towards   the  pleural  side  and 
in  radiating  bundles  towards  the  peritoneal  side. 

The  lymphatics  of  the  anterior  half  of  the  diaphragm  open  into  those  of 
the  anterior  mediastinum,  while  those  of  the  posterior  half  pass  into  a 
lymphatic  vessel  in  the  posterior  mediastinum,  which  soon  enters  the  thoracic 
duct.  Both  these  sets  of  vessels,  and  the  glands  into  which  they  pass,  are 
readily  injected  by  the  method  above  described  ;  and  there  can  be  little 
doubt  that  during  life  the  flow  of  lymph  along  these  channels  is  chiefly 
caused  by  the  action  of  the  diaphragm  during  respiration.  As  it  descends 
in  inspiration,  the  spaces  between  the  radiating  tendon  bundles  dilate, 
and  lymph  is  sucked  from  the  peritoneal  cavit}-.  through  the  widely  open 
stomata,  into  the  interfascicular  lymphatics.  During  expiration,  the  spaces 
between  the  concentric  tendon  bundles  dilate,  and  the  lymph  is  squeezed  into 
the  lymphatic-  towards  the  pleural  surface.  (Klein.)  It  thus  appears  probable 
that  during  health  there  is  a  continued  sucking  in  of  lymph  from  the  perito- 
neum into  the  lymphatics  by  the  ';  pumping"  action  of  the  diaphragm  :  and 
there  is  doubtless  an  equally  continuous  exudation  of  fluid  from  the  general 
serous  surface  of  the  peritoneum.  When  this  balance  of  transudation  and 
absorption  is  disturbed,  either  by  increased  transudation  or  some  impedi- 
ment to  absorption,  an  accumulation  of  fluid  necessarily  takes  place 
(ascites). 

Stomata  have  been  found  in  the  pleura;  and   as  they  may  be 

uned  to  exist  in  other  serous  membranes,  it  would  seem  as  if 
the  serous  cavities,  hitherto  supposed  closed,  form  but  a  large 
lymph-sinus  or  widening  out,  so  to  speak,  of  the  lymph-capillary 
Bystem  with  which  they  directly  communicate. 


^65  ABSORPTION.  ['hap.  ix. 

Structure  of  Lymphatic  Vessels. — The  larger  vessels  are 
very  like  veins,  having  an  external  coat  of  fibre-cellular  tissue, 
with  elastic  filaments  ;  within  this,  a  thin  layer  of  fibre-cellular 
tissue,  with  plain  muscular  fibres,  which  have,  principally,  a  cir- 
cular direction,  and  are  much  more  abundant  in  the  small  than  in 
the  larger  vessels  ;  and  again,  within  this,  an  inner  elastic  layer 
of  longitudinal  fibres,  and  a  lining  of  epithelium  ;  and  numerous 
valves.  The  valves,  constructed  like  those  of  veins,  and  with  the 
free  edges  turned  towards  the  heart,  are  usually  arranged  in  pairs, 
and,  in  the  small  vessels,  are  so  closely  placed,  that  when  the 
ressels  are  full,  the  valves  constricting  them  where  their  edges 
are  attached,  give  them  a  peculiar  beaded  or  knotted  ap- 
pearance. 

Current  of  the  Lymph. — With  the  help  of  the  valvular 
mechanism  (i)  all  occasional  pressure  on  the  exterior  of  the  lym- 
phatic and  lacteal  vessels  propels  the  lymph  towards  the  heart  : 
thus  muscular  and  other  external  pressure  accelerates  the  flow  of 
the  lymph  as  it  does  that  of  the  blood  in  the  veins.  The  actions 
of  (2)  the  muscular  fibres  of  the  small  intestine,  and  probably  the 
laver  of  organic  muscle  present  in  each  intestinal  villus,  seem  to 

ssist  in  propelling  the  chyle  :  for,  in  the  small  intestine  of  a 
mouse,  the  chyle  has  been  seen  moving  with  intermittent  propul- 
sions that  appeared  to  correspond  with  the  peristaltic  movements 
of  the  intestine.  But  for  the  general  propulsion  of  the  lymph 
and  chyle,  it  is  probable  that,  together  with  (3)  the  vis  a  forgo 
resulting  from  absorption  (as  in  the  ascent  of  sap  in  a  tree),  and 
from  external  pressure,  some  of  the  force  may  be  derived  (4) 
from  the  contractility  of  the  vessel's  own  walls.  The  respiratory 
movements,  also,  (5)  favour  the  current  of  lymph  through  the 
thoracic  duct  as  they  do  the  current  of  blood  in  the  thoracic  veins 

(P-  253)- 

Lymphatic   Glands  are  small  round  or  oval  compact  bodies 

varying  in  size  from  a  hempseed  to  a  bean,  interposed  in  the 
course  of  the  lymphatic  vessels,  and  through  which  the  chief 
part  of  the  lymph  passes  in  its  course  to  be  discharged  into  the 
blood  vessels.  They  are  found  in  great  mmibers  in  the  mesen- 
tery, and  along  the  great  vessels  of  the  abdomen,  thorax,  anc\ 
neck ;  in  the  axilla  and  groin  ;  a  few  in  the  popliteal  space,  but 
not  further  down  the  lesr,  and  in  the  arm  as  far  as  the  elbow. 


«ii.\p.  IX.]  LYMPHATIC    GLANDS.  369 

Some  lymphatics  do   not,  however,   pass  through   glands   before 
entering  the  thoracic  duet. 

Structure. — A  lymphatic  gland  is  covered  externally  by  a 
capsule  of  connective  tissue,  generally  containing  some  unstriped 
muscle.  At  the  inner  side  of  the  gland,  which  is  somewhat  con- 
cave (hilus)  ( fig.  2  1  2,  a),  the  capsule  scuds  processes  inwards  in  which 


Fig.  212. — Section  of  a  mesenteric  gland  from  the  ox,  slightly  magnified,  a,  Hilus;  b  (in 
the  central  part  of  the  figure),  medullary  substance  ;  <•,  cortical  substance  with  indis- 
tinct alveoli ;  d,  capsule  (Kulliker). 

the  blood  vessels  are  contained,  and  these  join  with  other  processes 
called  trabecules  (fig,  215,  t.r.)  prolonged  from  the  inner  surface  of 
the  part  of  the  capsule  covering  the  convex  or  outer  part  of  the 
gland  :  they  have  a  structure  similar  to  that  of  the  capsule,  and 
entering  the  gland  from  all  sides,  and  freely  communicating,  form 
a  fibrous  supporting  stroma.  The  interior  of  the  gland  is  seen 
on  section,  even  when  examined  with  the  naked  eye,  to  be  made 
up  of  two  parts,  an  outer  or  cortical  (fig.  212,  c}  c),  which  is 
light  coloured,  and  an  inner  of  redder  appearance,  the  medullary 
portion  (fig.  212).  In  the  outer  or  cortical  part  of  the  gland 
(fig.  215,  c)  the  intervals  between  the  trabecular  are  comparatively 
large  and  more  or  less  triangular,  the  intercommunicating  spaces 
being  termed  alveoli ;  whilst  in  the  more  central  or  medullary  part 
a  finer  meshwork  is  formed  by  the  more  free  anastomosis  of  the 
trabecular  processes.  In  the  alveoli  of  the  cortex  and  in  the 
meshwork  formed  by  the  trabecular  in  the  medulla,  is  contained 
the  proper  gland  structure.  In  the  former  it  is  arranged  as  follows 
(fig.  215) :  occupying  the  central  and  chief  part  of  each  alveolus,  is 
a  more  or  less  wedge-shaped  mass  (l.h.)  of  adenoid  tissue,  densely 
packed  with  lymph  corpuscles ;  but  at  the  periphery  surrounding 
the  central  portion  and  immediately  next  the  capsule  and  trabe 
cular,  is  a  more  open  meshwork  of  adenoid  tissue'  constituting  the 

b  1; 


37o 


ABSORPTION. 


[CHAP.  IX. 


lymph  sinus  or  channel  (l.s.),  and  containing  fewer  lymph  corpuscles; 
The  central  mass  is  enclosed  in  endothelium,  the  cells  of  which 


J 


? 


v. 


< 


. 


Fig.  213. — Front  a  vertical  section  through  the  capsule,  cortical  sinus  and  peripheral  portion  of 
follicle  of  a  human  compound  lymphatic  gland.  The  section  had  been  shaken,  so  as  to 
get  rid  of  most  of  the  lymph  corpuscles.  A.  Outer  stratum  of  capsule,  consisting  of 
bundles  of  fibrous  tissue  cut  at  various  angles.  B.  Inner  stratum,  showing  fibres  of 
connective  tissue  with  nuclei  of  flattened  connective-tissue  corpuscles.  Beneath  this 
(between  B  and  C)  is  the  lymph-sinus  or  lymph-path,  containing  a  reticulum  coated 
by  flat  nucleated  endothelial  cells.  C.  Fine  nucleated  endothelial  membrane,  marking 
boundary  of  the  lymph-follicle.  The  rest  of  the  section  from  C  to  E  is  the  adenoid 
tissue  of  the  lymph-follicle,  which  consists  of  a  fine  reticulum,  E,  with  numerous 
lymph  corpusles,  D.  They  are  so  closely  packed  that  the  adenoid  reticulum  is  invisible 
till  the  section  has  been  shaken  so  as  to  dislodge  a  number  of  the  lymph-corpuscles 
x  350  (Klein  and  Noble  Smith) . 


join  by  tHeir  processes,  the  processes  of  the  adenoid  framework  of 
the  lymph  sinus.  The  trabecule  are  also  covered  with  endothe- 
lium. The  lining  of  the  central  mass  does  not  prevent  the 
passage  of  fluids  and  even  of  corpuscles  into  the  lymph  sinus.  The 
framework  of  the  adenoid  tissue  of  the  lymph  sinus  is  nucleated, 
that  of  the  central  mass  is  non-nucleated.  At  the  inner  part  of 
the  alveolus,  the  wedge-shaped  central  mass  bifurcates  (fig.  215) 
or  divides  into  two  or  more  smaller  rounded  or  cord-like  masses 
and  here  joining  with  those  from  the  other  alveoli,  form  a  much 
closer  arrangement  of  the  gland  tissue  (fig.  214,  a)  than  in  the 
cortex;  spaces  (fig.  214,  b),  are  left  within  those  anastomosing 
cords,  in  which  are  found  portions  of  the  trabecular  meshwork 
and  the  continuation  of  the  lymph  sinus  (6,  c). 


CHAP.   ix.  J 


LYMPHATIC    <iI..\XDS. 


371 


The    essentia]    structure    of    lymphatic-gland     substance    re- 
sembles   that   which    was    described    as   existing,    in    a    simple 


Fig.  214. — Section  of  medullary  substance  of  an  inguinal  gland  of  an  ox];  a,  a,  glandular 
substance  or  pulp  forming  rounded  cords  joining  in  a  continuous  net  (dark  in  the 
figure)  ;  c.  c,  trabecule  ;  the  space,  b,  b,  between  these  and  the  glandular  substance  is 
the  lymph-sinus,  washed  clear  of  corpuscles  and  traversed  by  filaments  of  retiform 
connective-tissue  X  90  (Kolliker). 


Fig.  215.— Diagrammatic  section  of  Lymphatic  gland,  a.  /.,  Afferent ;  e.  T.  efferent  lympha- 
tics; (7,  cortical  substance;  l.h.,  reticulating  cords  of  medullary  .substance  ;  I.  ?., 
lymph-sinus ;  c,  fibrous  coat  sending  in  trabecular  ;  t.  r.,  into  the  substance  of  the 
gland  (Sharpey). 

B   B   2 


372 


ABSORPTION. 


[chap.  IX. 


form,  in  the  interior  of  the  solitary  and  agminated  intestinal 
follicles. 

The  lymph  enters  the  gland  by  several  afferent  vessels  (fig. 
215,  a.l.)  which  open  beneath  the  capsule  into  the  lymph-channel 
or  lymph-path ;  at  the  same  time  they  lay  aside  all  their  coats 
except  the  endothelial  lining,  which  is  continuous  with  the  lining 
of  the  lymph-path.  The  efferent  vessels  (fig.  215,  e.l.)  begin  in  the 
medullary  part  of  the  gland,  and  are  continuous  with  the  lymph- 
path  here  as  the  afferent  vessels  were  with  the  cortical  portion  ; 
the  endothelium  of  one  is  continuous  with  that  of  the  other. 

The  efferent  vessels  leave  the  gland  at  the  hilus,  the  more  or 
less  concave  inner  side  of  the  gland,  and  generally  either  at  once 
or  very  soon  after  join  together  to  form  a  single  vessel. 

Blood-vessels  which  enter  and  leave  the  gland  at  the  hilus  are 


Fig.  216. — A  small  portion  of  medullary  substance  from  a  mesenteric  gland  of  the  ox,  d,  d, 
trabecule©  ;  a,  part  of  a  cord  of  glandular  substances  from  which  all  but  a  few  of  the 

lymph-corpuscles  have  been  washed  out  to  show  its  supporting  meshwork  of  retiform 
tissue  and  its  capillary  blood-vessels  (which  have  been  injected,  and  are  dark  in  the 
figure)  ;  b,  b,  lymph-sinus,  of  which  the  retiform  tissue  is  represented  only  at  c,  c. 

X  300  (Kolliker). 

freely  distributed  to  the  trabecular  tissue  and  to  the  gland-pulp 
(fig.  216). 


CHAP,  ix.]  LYMPH    AND    CHYLE.  -y - 

The  tonsils,  in  part,  and  Payer's  glands   of  the  intestine, 
really  lymphatic  glands,  and  doubtless  discharge  similar  functions. 

The  Lymph  and  Chyle. 

The  lymph,  contained  in  the  lymphatic  vessels,  is,  under  ordi- 
nary circumstances,  a  clear,  transparent,  and  yellowish  fluid.  It 
is  devoid  of  smell,  is  slightly  alkaline,  and  has  a  saline  taste.  As 
seen  with  the  microscope  in  the  small  transparent  vessels  of  the 

tail  of  the  tadpole,  it  usually  contains  no  corpuscles  or  particles 
of  any  kind  ;  and  it  is  only  in  the  larger  trunks  in  which  any 
corpuscles  are  to  be  found.  These  corpuscles  are  similar  to 
colourless  blood-corpuscles.  The  fluid  in  which  the  corpuscles 
float  is  albuminous,  and  contains  no  fatty  particles  or  molecular 

s  :  but  is  liable  to  variations  according  to  the  general  state  of 
the  blood,  and  to  that  of  the  organ  from  which  the  lymph  is 
derived.  As  it  advances  towards  the  thoracic  duct,  and 
after  passing  through  the  lymphatic  glands,  it  becomes  spon- 
taneously coagulable  and  the  number  of  corpuscles  is  much 
increased.  The  fluid  contained  in  the  lacteals  is  clear  and 
transparent  during  fasting,  and  differs  in  no  respect  from  ordi- 
nary lymph ;  but,  during  digestion,  it  becomes  milky,  and  is 
termed  chyle. 

Chyle  is  an  opaque,  whitish,  milky  fluid,  neutral  or  slightly 
alkaline  in  reaction.  Its  whiteness  and  opacity  are  due  to  the 
presence  of  innumerable  particles  of  oily  or  fatty  matter,  of 
exceedingly  minute  though  nearly  uniform  size,  measuring  on  the 
average  about  30*00  of  an  inch.  These  constitute  what  is 
termed  the  molecular  base  of  chyle.  Their  number,  and  conse- 
quently the  opacity  of  the  chyle,  are  dependent  upon  the  quantity 
of  fatty  matter  contained  in  the  food.  The  fatty  nature  of  the 
molecules  is  made  manifest  by  their  solubility  in  ether,  and,  when 
the  ether  evaporates,  by  their  being  deposited  in  various-sized 
drops  of  oil.  Each  molecule  probably  consists  of  oil  coated  over 
with  albumen,  in  the  manner  in  which  oil  always  becomes  covered 
when  set  free  in  minute  drops  in  an  albuminous  solution.  This 
is  proved  when  water  or  dilute  acetic  acid  is  added  to  chyle,  many 
of  the  molecules  are  lost  sight  of,  and  oil-drops  appear  in  their 
place,  as  the  investments  of  the  molecules  have  beeu  dissolved,  and 
their  oily  contents  have  run  together. 


374  ABSOEPTION.  [chap.  ix. 

Except  these  molecules,  the  chyle  taken  from  the  villi  or  from 
lacteals  near  them,  contains  no  other  solid  or  organised  bodies. 
The  fluid  in  which  the  molecules  float  is  albuminous,  and  does  not 
spontaneously  coagulate.  But  as  the  chyle  passes  on  towards  the 
thoracic  duct,  and  especially  while  it  traverses  one  or  more  of  the 
mesenteric  glands,  it  is  elaborated.  The  quantity  of  molecules 
and  oily  particles  gradually  diminishes ;  cells,  to  which  the  name 
of  chyle-corpuscles  is  given,  are  developed  in  it ;  and  it  acquires 
the  property  of  coagulating  spontaneously.  The  higher  in  the 
thoracic  duct  the  chyle  advances,  the  more  is  it,  in  all  these 
respects,  developed  ;  the  greater  is  the  number  of  chyle-corpuscles, 
and  the  larger  and  firmer  is  the  clot  which  forms  in  it  when 
withdrawn  and  left  at  rest.  Such  a  clot  is  like  one  of  blood 
without  the  red  corpuscles,  having  the  chyle  corpuscles  entangled 
in  it,  and  the  fatty  matter  forming  a  white  creamy  film  on  the 
surface  of  the  serum.  But  the  clot  of  chyle  is  softer  and  moister 
than  that  of  blood.  Like  blood,  also,  the  chyle  often  remains  for  a 
long  time  in  its  vessels  without  coagulating,  but  coagulates  rapidly 
on  being  removed  from  them.  The  existence  of  the  materials 
which,  by  their  union  form  fibrin,  is,  therefore,  certain  •  and  their 
increase  appears  to  be  commensurate  with  that  of  the  corpuscles. 

The  structure  of  the  chyle-corpuscles  was  described  when  speak- 
ing of  the  white  corpuscles  of  the  blood,  with  which  they  are 
identical. 

Chemical  Composition  of  Lymph  and  Chyle. — From  what 
has  been  said,  it  will  appear  that  perfect  chyle  and  lymph  are,  in 
essential  characters,  nearly  similar,  and  scarcely  differ,  except  in 
the  preponderance  of  fatty  and  proteid  matter  in  the  chyle. 

Chemical  Composition  of  Lymph  and  Chyle    (Owen  Eees). 

i.  ii.  in. 

Lymph            ( Ihyle  Mixed  Lvmph  & 

(Donkey).  (Donkey).  Chyle  (Human). 

Water 96*536  90237  90-48 

Solids 3-454        9763  9'52 


Solids — 

P  rote  ids.   including    Serum-  Albu-    )  i--2o             "-886            vo8 

min.  Fibrin,  and  Globulin.          .    /  J 

Extractives,  including  in  (1  and  1)  1  6              .iog 

Sugar,  Urea,  Leucin  k  Cholesterin  /  -°                 ->  -) 

Fatty  matter a  trace           3'6oi               '92 

Salts -585               711              -44 


chap.  EC]  ABSOBPTION    l:V    LACTEAIA  37c 

From  the  above  analyses  of  lymph  and  chyle,  it  app 
that  they  contain  essentially  the  Banie  constituents  thai  are 
found  in  the  blood.  Their  composition,  indeed,  differs  from  thai 
of  the  blood  in  degree  rather  than  in  kind.  They  do  not,  how- 
by  accident,  contahi  coloured  corpuscles, 
entity. — The  quantity  which  would  pass  into  a  cat's  blood  in 
twenty-four  hours  has  been  estimated  to  be  equal  to  about  one-sixth 
ofthe  weight  of  the  whole  body.  And,  since  the  estimated  weight 
of  the  blood  in  rats  is  to  the  weight  of  their  bodies  as  17,  the 
quantity  of  lymph  daily  traversing  the  thoracic  duct  would 
appear  to  be  about  equal  to  the  quantity  of  blood  at  any  time 
contained  in  the  animals.  By  another  scries  of  experiments,  the 
quantity  of  lymph  traversing  the  thoracic  duct  of  a  dog  in  twenty- 
four  hours  was  found  t<>  be  about  equal  t<>  two-thirds  of  the  blood 
in  the  body.     (Bidder  and  Schmidt) 

Absorption  by  the  Lacteals. — During  the  passage  of  the 
chyme  along  the  whole  tract  of  the  intestinal  canal,  its  com- 
pletely digested  parts  are  absorbed  by  the  blood-vessels  and  lac- 
teals distributed  in  the  mucous  membrane.  The  blood-vessels 
appear  to  absorb  chiefly  the  dissolved  portions  of  the  food,  and 
these,  including  especially  the  albuminous  and  saccharine,  they 
imbibe  without  choice  :  whatever  can  mix  with  the  blood  passes 
into  the  vessels,  as  will  be  presently  described.  But  the  lacteals 
appear  to  absorb  only  certain  constituents  of  the  food,  including 
particularly  the  fatty  portions.  The  absorption  by  both  sets  of 
vessels  is  carried  on  most  actively  but  not  exclusively,  in  the  villi 
of  the  small  intestine  ;  for  in  these  minute  processes,  both  the 
capillary  blood-vessels  and  the  lacteals  are  brought  almost  into 
contact  with  the  intestinal  contents.  There  seems  to  be  no  doubt 
that  absorption  of  fatty  matters  during  digestion,  from  the 
contents  of  the  intestines,  is  effected  chiefly  between  the  epithelial 
cells  which  line  the  intestinal  tract  (Watney),  and  especially 
those  which  clothe  the  surface  of  the  villi.  Thence,  the  fatty 
particles  are  passed  on  into  the  interior  of  the  lacteal  vessels  (fig. 
216,  a),  but  how  they  pass,  and  what  laws  govern  their  so  doing, 
are  not  at  present  exactly  known. 

The  process  of  absorption  is  assisted  by  the  pressure  exercised 
on  the  contents  of  the  intestines  by  their  contractile  walls;  and 
the  absorption  of  fatty  particles  is  also  facilitated  by  the  presence 


376  ABSORPTION,  [chap.  ix. 

of  the  bile,  and  the  pancreatic  and  intestinal  secretions,  which 
moisten  the  absorbing  surface.  For  it  has  been  found  by  experi- 
ment, that  the  passage-  of  oil  through  an  animal  membrane  is 
made  much  easier  when  the  latter  is  impregnated  with  an  alkaline 
fluid. 

Absorption  by  the  Lymphatics. — The  real  source  of  the 
lymph,  and  the  mode  in  which  its  absorption  is  effected  by  the 
lymphatic  vessels,  were  long  matters  of  discussion.  But  the 
problem  has  been  much  simplified  by  more  accurate  knowledge  of 
the  anatomical  relations  of  the  lymphatic  capillaries.  The  lymph 
is,  without  doubt,  identical  in  great  part,  with  the  liquor  sanguinis, 
which,  as  before  remarked,  is  always  exuding  from  the  blood- 
capillaries  into  the  interstices  of  the  tissues  in  which  they  lie ;  and 
as  these  interstices  form  in  most  parts  of  the  body  the  beginnings 
of  the  lymphatics,  the  source  of  the  lymph  is  sufficiently  obvious. 
In  connection  with  this  may  be  mentioned  the  fact  that 
changes  in  the  character  of  the  lymph  correspond  very  closely 
with  changes  in  the  character  of  either  the  whole  mass  of  blood, 
or  of  that  in  the  vessels  of  the  part  from  which  the  lymph  is 
exuded.  Thus  it  appears  that  the  coagulability  of  the  lymph  is 
directly  proportionate  to  that  of  the  blood ;  and  that  when  fluids 
are  injected  into  the  blood-vessels  in  sufficient  quantity  to  distend 
them,  the  injected  substance  may  be  almost  directly  afterwards 
found  in  the  lymphatics. 

Some  other  matters  than  those  originally  contained  in  the 
exuded  liquor  sanguinis  may,  however,  find  their  way  with  it 
into  the  lymphatic  vessels.  Parts  which  having  entered  into 
the  composition  of  a  tissue,  and,  having  fulfilled  their  purpose, 
require  to  be  removed,  may  not  be  altogether  excrementitious, 
but  may  admit  of  being  re-organised  and  adapted  again  for 
nutrition ;  and  these  may  be  absorbed  by  the  lymphatics,  and 
elaborated  with  the  other  contents  of  the  lymph  in  passing 
through  the  glands. 

Lymph-Hearts. — In  reptiles  and  some  birds,  an  important  auxiliary  to 
the  movement  of  the  lymph  and  chyle  is  supplied  in  certain  muscular  sacs, 
named  lymph-hearts  (fig.  217),  and  it  has  been  shown  that  the  caudal  heart  of 
the  eel  is  a  lymph-heart  also.  The  number  and  position  of  these  organs  vary. 
In  frogs  and  toads  there  are  usually  four,  two  anterior  and  two  posterior  ;  in 
the  frog,  the  posterior  lymph-heart  on  each  side  is  situated  in  the  ischiatic  re- 
gion, just  beneath  the  skin  ;  the  anterior  lies  deeper,  just  over  the  transverse 


CHAP.  IX. J 


ABSORPTION    BY    BLOODS 


:  :  the  third  vesxi 

,  the  orifices  of  tl  tg  guard  t  the 

mph.   Pi 

conveys  t he  lymph  directly  into  the  :i.     In  the  f:  ferior 

lymphatic  heart,  on  each  n  lymph  into  a  branch  of  the  ischiatic 

by  the  -  ■  the  lymph  is  forced  into  a  branch  of   the   jugular 

vein,  which  isfi  rior  surface,  and  which  becomes  turgid 

time  that  the  sac  contra  its,     Bl     d    -  ted  from  passing  from  th 

he  lymphatic  heart  by  a  valve  atite 

muscular  coat  of  these  hearts  is  of  variable  thick  some  cases  it 

can  only  I        -      ered  by  means  of  the  microscope  ;  but  in  every  case  it  is 
cunij  jtripedfil  _  contractions  of  the  hearts  are  rhythmical, 


Fig.  217. — Lgmj  -  Python 

bi>  The  external  cellular  coat.    5.  The  thick  muscular  coat.    Four  muscular 

columns  run  across  its  cavity,  which  communicates  with  three  lymphatics    1 — only  one 

^nd  with  two  veins   2.  2  .     6.  The  smooth  lining  membrane  of  the  1 
-    A  small  appendage,  or  auricle,  the  cavity  of  which  is  continuous  with  that  of  the 
rest  of  the  organ  (after  B.  Weber  . 

occurring  about  sixty  times  in  a  minute,  slowly,  and.  in  comparison  with 
of  the  blood-hearts,  feebly.      The  pulsations   of  the  cervical  pair  are  not 
always  synchronous  with  those  of  the  pair  in  the  ischiatic  region,  and  even 
the  corresponding  sacs  of  opposite  sides  are  not  always  synchronous  in  their 
action. 

Unlike  the  contractions  of  the  blood-heart,  those  of  the  lymph-heart 
appear  to  be  directly  dependent  upon  a  certain  limited  portion  of  the  spinal 
cord.  For  Yolkniann  found  that  so  long  as  the  portion  of  spinal  cord 
corresponding  to  the  third  vertebra  of  the  frog  was  uninjured,  the  cervical 
pair  of  lymphatic  hearts  continued  pulsating  after  all  the  rest  of  the  spinal 
cord  and  the  brain  were  desl  while  destruction  of  this  portion, 

though  all  other  pans  of  the  nervous  centres  were  uninjured,  instantly 
•-•d  the  heart's  movements.  The  posterior,  or  ischiatic,  pair  of  lymph- 
hearts  were  found  to  be  governed,  in  like  manner,  by  the  portion  of  spinal 
cord  corresponding  to  the  eighth  vertebra.  Division  of  the  posterior  spinal 
roots  did  not  arrest  the  movements  ;  but  division  of  the  anterior  roots 
caused  them  to  cease  at  once. 


Absorption  by  Blood-vessels. — In    the    absorption   by   the 


3/8 


ABSORPTION. 


[CHAP.   IX. 


lymphatic  or  lacteal  vessels  just  described,  there  appears  some- 
thing like  the  exercise  of  choice  in  the  materials  admitted  into 
them.  But  the  absorption  by  blood-vessels  presents  no  such 
appearance  of  selection  of  materials;  rather,  it  appears,  that  every 
substance,  whether  gaseous,  liquid,  or  a  soluble,  or  minutely 
divided  solid,  may  he  absorbed  by  the  blood-vessels,  provided  it  is 
capable  of  permeating  their  walls,  and  of  mixing  with  the  blood ; 
and  that  of  all  such  substances,  the  mode  and  measure  of  absorp- 
tion are  determined  solely  by  their  physical  or  chemical  properties 
and  conditions,  and  by  those  of  the  blood  and  the  walls  of  the 
blood-vessels. 

Osmosis. — The  phenomena  are,  indeed,  to  a  great  extent,  com- 
parable to  that  passage  of  fluids  through  membrane,  which  occurs 
quite  independently  of  vital  conditio  >ns,  and  the  earliest 
_  and  best  scientific  investigation  of  which  was  made 

by  Dutrochet.  The  instrument  which  he  employed 
in  his  experiments  was  named  an  endosmometer.  It 
may  consist  of  a  graduated  tube  expanded  into  an 
open-mouthed  bell  at  one  end,  over  which  a  portion 
of  membrane  is  tied  (fig.  218).  If  now  the  bell  be 
filled  with  a  solution  of  a  salt — say  sodium  chloride, 
and  be  immersed  in  water,  the  water  will  pass  into 
the  solution,  and  part  of  the  salt  will  pass  out  into 
the  water  ;  the  water,  however,  will  pass  into  the 
solution  much  more  rapidly  than  the  salt  will  pass 
out  into  the  water,  and  the  diluted  solution  will  rise 
in  the  tube.  To  this  passage  of  fluids  through 
membrane  the  term  Osmosis  is  applied. 

The  nature  of  the  membrane  used  as  a  septum, 
and  its  affinity  for  the  fluids  subjected  to  experiment 
have  an  important  influence,  as  might  be  anticipated, 
on  the  rapidity  and  duration  of  the  osmotic  current. 
Thus,  if  a  piece  of  ordinary  bladder  be  used  as 
the  septum  between  water  and  alcohol,  the  current  is  almost 
solely  from  the  water  to  the  alcohol,  on  account  of  the  much 
greater  afnnitv  of  water  for  this  kind  of  membrane ;  while,  on  the 
other  hand,  in  the  case  of  a  membrane  of  caoutchouc,  the  alcohol, 
from  its  greater  affinity  for  this  substance,  would  pass  freely  into 
the  water. 


Fig.  218.— End 
osmometer. 


<  hat.  ix.]  0SM08IS.  3-9 

Osmosis  by  Blood-vessels.  —  Absorption    by    blood  -  vessels 
is   the  consequence  of  Iheir  walls  being,  like  tin-  membranous 

I'tiini  <>t*  the  endosmometer,  porous  and  capable  of  imbibing 
iiuMs,  ami  of  the  blood  being  bo  composed  that  most  fluids  will 
mingle  with  it.  The  process  of  absorption,  in  an  instructive, 
though  very  imperfect  degree,  may  l>c  observed  in  any  portion  of 
vascular  tissue  removed  from  the  body,  [f  such  a  one  be  placed 
in  a  vessel  of  water,  it  will  shortly  swell,  and  become  heavier  and 
moister,  through  the  quantity  of  water  imbibed  or  soaked  into  it  ; 
and  if  now,  the  blood  contained  in  any  of  its  vessels  be  let  out, 
it  will  be  found  diluted  with  water,  which  lias  been  absorbed  by 
the  blood-vessels  and  mingled  with  the  blood.  The  water  round 
the  piece  of  tissue  also  will  become  blood-stained  ;  and  if  all  be 
kept  at  perfect  rest,  the  stain  derived  from  the  solution  of  the 
colouring  matter  of  the  blood  (together  with  which  chemistry 
would  detect  some  of  the  albumen  and  other  parts  of  the  liquor 
sanguinis)  will  spread  more  widely  every  day.  The  same  will 
happen  if  the  piece  of  tissue  be  placed  in  a  saline  solution  instead 
of  water,  or  in  a  solution  of  colouring  or  odorous  matter,  either  of 
which  will  give  their  tinge  or  smell  to  the  blood,  and  receive,  in 
exehange,  the  colour  of  the  blood. 

Colloids  and  Crystalloids. — Various  substances  have  been 
classified  according  to  the  degree  in  which  they  possess  the  pro- 
perty of  passing,  when  in  a  state  of  solution  in  water,  through 
membrane  ;  those  which  pass  freely,  inasmuch  as  they  are  usually 
capable  of  crystallization,  being  termed  crystalloids,  and  those 
which  pass  with  difficulty,  on  account  of  their,  physically,  glue- 
like characters,  colloids.     (Graham.) 

This  distinction,  however,  between  colloids  and  crystalloids 
which  is  made  the  basis  of  their  classification,  is  by  no  means 
the  only  difference  between  them.  The  colloids,  besides  the 
absence  of  power  to  assume  a  crystalline  form,  are  characterised 
by  their  inertness  as  acids  or  bases,  and  feebleness  in  all  ordinary 
chemical  relations.  Examples  of  them  are  found  in  albumin, 
gelatin,  starch,  hydrated  alumina,  hydrated  silicic  acid,  etc. ; 
while  the  crystalloids  are  characterised  by  qualities  the  reverse 
of  those  just  mentioned  as  belonging  to  colloids.  Alcohol,  sugar, 
and  ordinary  saline  substances  are  exanrples  of  crystalloids. 

Rapidity  of  Absorption. — The  rapidity  with  which  matters 


3 So  ABSORFTIOX.  [chap.  ix. 

may  be  absorbed  from  the  stomach,  probably  by  the  blood-vessels 
chiefly,  and  diffused  through  the  textures  of  the  body,  may  be 
gathered  from  the  history  of  some  experiments.  From  these  it 
appears  that  even  in  a  quarter  of  an  hour  after  being  given  on  an 
empty  stomach,  lithium  chloride  may  be  diffused  into  all  the 
vascular  textures  of  the  body,  and  into  some  of  the  non-vascular, 
as  the  cartilage  of  the  hip-joint,  as  well  as  into  the  aqueous 
humour  of  the  eye.  Into  the  outer  part  of  the  crystalline  lens 
it  may  pass  after  a  time,  varying  from  half  an  hour  to  an  hour 
and  a  half.  Lithium  carbonate,  when  taken  in  five  or  ten-grain 
doses  on  an  empty  stomach,  may  be  detected  in  the  urine  in  5  or 
1  o  minutes  ;  or,  if  the  stomach  be  full  at  the  time  of  taking  the 
dose,  in  20  minutes.  It  may  sometimes  be  detected  in  the  urine, 
moreover,  for  six,  seven,  or  eight  days.     (Bence  Jones.) 

Some  experiments  on  the  absorption  of  various  mineral  and 
vegetable  poisons,  have  brought  to  light  the  singular  fact,  that,  in 
some  cases,  absorption  takes  place  more  rapidly  from  the  rectum 
than  from  the  stomach.  Strychnia,  for  example,  when  in  solution, 
produces  its  poisonous  effects  much  more  speedily  when  introduced 
into  the  rectum  than  into  the  stomach.  When  introduced  in  the 
solid  form,  however,  it  is  absorbed  more  rapidly  from  the  stomach 
than  from  the  rectum,  doubtless  because  of  the  greater  solvent 
property  of  the  secretion  of  the  former  than  of  that  of  the  latter. 
(Savory.) 

With  regard  to  the  degree  of  absorption  by  living  blood-vessels, 
much  depends  on  the  facility  with  which  the  substance  to  be 
absorbed  can  penetrate  the  membrane  or  tissue  which  lies 
between  it  and  the  blood-vessels.  Thus,  absorption  will  hardly 
take  place  through  the  epidermis,  but  is  quick  when  the  epidermis 
is  removed,  and  the  same  vessels  are  covered  with  only  the  surface 
of  the  cutis,  or  with  granulations.  In  general,  the  absorption 
through  membranes  is  in  an  inverse  proportion  to  the  thickness 
of  their  epithelia ;  so  that  the  urinary  bladder  of  a  frog  is 
traversed  in  less  than  a  second  ;  and  the  absorption  of  poisons  by 
the  stomach  or  lungs  appears  sometimes  accomplished  in  an 
immeasurably  small  time. 

Conditions  for  Absorption.— 1.  The  substance  to  be  ab- 
sorbed must,  as  a  general  rule,  be  in  the  liquid  or  gaseous  state, 
or,  if  a  solid,  must  be  soluble  in  the  fluids  with  which  it  is  brought 


chap,  rx.]  CONDITIONS    FOB    AB80RPTTON.  3S1 

utact.     II- :.      the  marks  of  *  _.  and  the  discoloration 

produced  by  diver  nitrate  taken  internally,  remain.      Mercury 
may  rbed  even  in  the  metal]  ;  and  in  tli  may 

into  and  remain   in  the  blood  from 

them;  and  such  subetai  edingly  finely-divided  char 

when  taken  into  the  alimentary  canal,  have  been  found  in  the 

nteric  veins;  the  insoluble  materials  of  ointments  may  also 

ibbed  into  the  blood-vest  U  ;  but  there  are  no  facte  to  d 
mine  how  these    various   substances   effect    their   passage.      Oil, 
minutely   divided,    as    in    an    emulsion,    will    p  ly    into 

blood- ve—  Is,  -  it  will  through  a  filter  moistened  with  water: 
and.  without  doubt,  fatty  matters  find  their  way  into  the 
blood-w—  Lb  -  well  as  the  lymph -v..—  Lb  f  the  intestinal 
canal,  although  the  latter  seem  to  be  specially  intended  for  their 
■ 

2.  The  less  dense  the  fluid  to  be      -       sd,  the  more  speedy,    - 
eral  rule,  is  its  absorption  by  the  living  blood-vessels.     Hence 

the  rapid   absorption  <:>f  water  from  the  stomach  :  also  of  weak 
saline  solutions:  but   with  strong  solutions,  there    appears   less 
rption  into,  than  effusion  from,  the  blood-       • 

3.  The  absorption  is  the  less  rapid  the  fuller  and  tenser  the 
blood-vessels  are  :  and  the  tension  may  be  so  great  as  to  hinder 
altogether  the  entrance  of  more  fluid.  Thus,  if  water  is  injc  I 
into  a  dog's  veins  to  repletion,  poison  is  absorbed  very  slowly; 
but  when  the  tension  of  the  -  Is  is  diminished  by  bleeding,  the 
poison  acts  quickly.  So,  when  cupping-g]  -  3  laced  over  a 
poisoned  wound,  they  retard  the  absorption  of  the  poison  not  only 
by  diminishing  the  velocity  of  the  circulation  in  the  part,  but  by 
filling  all  its  vessels  too  full  to  admit  more. 

On  the  same  ground,  absorption  is  the  quicker  the  more  rapid 
the  circulation  of  the  blood  :  n<  »t  because  the  fluid  to  be  absorbed 
is  more  quickly  imbibed  into  the  tissue-,  or  mingled  with  the 
blood,  but  because  as  East  as  it  enters  the  blood,  it  is  earned  away 
from  the  part,  and  the  blood  being  constantly  renewed,  is  con- 
stantly as  fit  as  at  the  first  for  the  reception  of  the  substance  to 
be  absorbed. 


o  52  AJTEMAL   HEAT.  [chap.  x. 


CHAPTEE   X. 

ANIMAL   HEAT. 

The  Average  Temperature  of  the  human  body  in  those  internal 
parts  which  are  most  easily  accessible,  as  the  mouth  and  rectum, 
is  from  98-5°  to  99-5°  F.  (36-9°— 37-4°  C).  In  different  parts  of 
the  external  surface  of  the  human  body  the  temperature  varies 
only  to  the  extent  of  two  or  three  degrees  (F.),  when  all  are  alike 
protected  from  cooling  influences ;  and  the  difference  which  under 
these  circumstances  exists,  depends  chiefly  upon  the  different 
degrees  of  blood-supply.  In  the  arm-pit — the  most  convenient 
situation,  under  ordinary  circumstances,  for  examination  by  the 
thermometer — the  average  temperature  is  98-6°  F.  (36*9°  C).  In 
different  internal  parts,  the  variation  is  one  or  two  degrees  ;  those 
parts  and  organs  being  warmest  which  contain  most  blood,  and  in 
which  there  occurs  the  greatest  amount  of  chemical  change,  e.g., 
the  glands  and  the  muscles ;  and  the  temperature  is  highest,  of 
course,  when  they  are  most  actively  working :  while  those  tissues 
which,  subserving  only  a  mechanical  function,  are  the  seat  of 
least  active  circulation  and  chemical  change,  are  the  coolest. 
These  differences  of  temperature,  however,  are  actually  but  slight, 
on  account  of  the  provisions  which  exist  for  maintaining  uniformity 
of  temperature  in  different  parts. 

Circumstances  causing  Variations  in  Temperature.— 
The  chief  circumstances  by  which  the  temperature  of  the  healthy 
body  is  influenced  are  the  following  : — Age  ;  Sex  :  Period  of  the 
day  ;  Exercise  ;  Climate  and  Season  ;  Food  and  Drink. 

Age. — The  average  temperature  of  the  new-born  child  is  only 
about  ic  F.  (*54c  C.)  above  that  proper  to  the  adult ;  and  the 
difference  becomes  still  more  trifling  during  infancy  and  early 
childhood.  The  temperature  falls  to  the  extent  of  about  "2° — *5°  F. 
from  early  infancy  to  puberty,  and  b}T  about  the  same  amount 
from  puberty  to  fifty  or  sixty  years  of  age.  In  old  age  the  tem- 
perature again  rises,  and  approaches  that  of  infancy  ;  but  although 
this  is  the  case,  yet  the  power  of  resisting  cold  is  less  in  them — 


ciim'.  x.|  VABIATI0N8    IN    TJSMPEBATTTRE.  383 

exposure  to  a  low  temperature  causing  a  greater  reduction  of  heat 
than  in  young  persons. 

The  same  rapid  diminution  of  temperature  has  been  observed  to  occur  in 
the  new-born  young  of  most  carnivorous  and  rodent  animals  when  th< 
removed  from  the  parent,  the  temperature  of  the  atmosphere  beii 
5oJ  and  53-5'  P.   (io°-i2°  ('.)  ;  whereas  while  Lying  close  to  the  b 
the.  mother,  their  temperature  is  only  2  or 3 degrees  I',  lower  than  b 
same  law  applies  to  the  young  of  birds. 

. — The  average  temperature  of  the  female  would  appear  to 
be  very  slightly  higher  than  that  of  the  male. 

Period  of  the   Day,  —  The  temperature   undergoes   a    gradual 

alteration,  to  the  extent  of  about  i°  to  1-5°  F.  (-54 — -8°  C.)  in 
the  course  of  the  day  and  night  ;  the  minimum  being  at  night 
or  in  the  early  morning,  the  maaimum  late  in  the  afternoon. 

Exercise. — Active  exercise  raises  the  temperature  of  the  body 
fn»m  i°  to  2°  F.  (-54° — ro8°C).  This  may  be  partly  ascribed 
to  generally  increased  combustion-processes,  and  partly  to  the  fact, 
that  every  muscular  contraction  is  attended  by  the  development 
of  one  or  two  degrees  of  heat  in  the  acting  muscle ;  and  that  the 
heat  is  increased  according  to  the  number  and  rapidity  of  these 
contractions,  and  is  quickly  diffused  by  the  blood  circulating  from 
the  heated  muscles.  Possibly,  also,  some  heat  may  lie  generated 
in  the  various  movements,  stretchings,  and  recoilings  <»f  the  other 
tissues,  as  the  arteries,  whose  elastic  walls,  alternately  dilated  and 
contracted,  may  give  out  some  heat,  just  as  caoutchouc  alternately 
stretched  and  recoiling  becomes  hot.  But  the  heat  thus  developed 
cannot  be  great.  The  great  apparent  increase  of  heat  during 
exercise  depends,  in  a  great  measure,  on  the  increased  circulation 
and  quantity  of  blood,  and,  therefore,  greater  heat,  in  parts  of 
the  body  (as  the  skin,  and  especially  the  skin  of  the  extremities), 
which,  at  the  same  time  that  they  feel  more  acutely  than  others 
any  changes  of  temperature,  are,  under  ordinary  conditions,  by 
some  degrees  colder  than  organs  more  centrally  situated. 

Climate  cend  Season. — The  temperature  of  the  human  body  is 
the  same  in  temperate  and  tropical  climates.  (Johnson,  Boileau, 
Purnell.)  In  summer  the  temperature  of  the  body  is  a  little 
higher  than  in  winter;  the  difference  amounting  to  about  a  third 
of  a  degree  F.     (Wunderlich.) 

Food  and  Drink. — The  effect  of  a  meal  upon  the  temperature 


384  ANIMAL    HEAT.  [chap.  x. 

of  a  body  is  but  small.  A  very  Blight  rise  usually  occurs.  Cold 
alcoholic  drinks  depress  the  temperature  somewhat  ("5°  to  i°  F.). 
AVarm  alcoholic  drinks,  as  well  as  warm  tea  and  coffee,  raise  the 
temperature  (about  -5°  F.). 

In  disease  the  temperature  of  the  body  deviates  from  the  normal 
standard  to  a  greater  extent  than  would  be  anticipated  from  the 
Blight  effect  of  external  conditions  during  health.  Thus,  in  some 
diseases,  as  pneumonia  and  typhus,  it  occasionally  rises  as  high  us 
106"  or  ic;:  F.  (410 — 4i'6°  < '.".  i  :  and  considerably  higher  tempe- 
ratures have  been  noted.  In  Asiatic  cholera,  on  the  other  hand, 
a  thermometer  placed  in  the  mouth  may  sometimes  rise  only  to 
77"-  or  79/  F.  (25"-— 26-2"  C.  . 

The  temperature  maintained  by  Mammalia  in  an  active  state  of  life, 
according  to  the  tables  of  Tiedemann  and  Rudolphi,  average-  ioi°  (38.3°  C.) 
The  extremes  recorded  by  them  were  96'  and  106°.  the  former  in  the  nar- 
whal, the  latter  in  a  bat  (Vespertilio  pipistrella).  In  Birds,  the  average 
is  as  high  as  I07D  (41  "2"  C.  :  the  highest  temperature,  111*25°  (4-6'2'  C.)  ; 
being  in  the  small  species,  the  linnets.  &c.  Among  Eeptiles.  while  the 
medium  they  were  in  was  75 :  (23-9''  C.)  their  average  temperature,  was 
82*5°  (3 1  '2°  C).  As  a  general  rule,  their  temperature,  though  it  falls  with 
that  of  the  surrounding  medium,  is.  in  temperate  media,  two  or  more  degrees 
higher  ;  and  though  it  rises  also  with  that  of  the  medium,  yet  at  very  high 
degrees  it  ceases  to  do  so.  and  remains  even  lower  than  that  of  the  medium. 
Fish  and  invertebrata  present,  as  a  general  rule,  the  same  temperature  as 
the  medium  in  which  they  live,  whether  that  be  high  or  low  ;  only  among 
fish,  the  tunny  tribe,  with  strong  hearts  and  red  meat-like  muscles,  and 
more  blood  than  the  average  of  fish  have,  are  generally  7"  (3*8'  C.)  warmer 
than  the  water  around  them. 

The  difference,  therefore,  between  what  are  commonly  called  the  warm 
and  the  cold-blooded  animals,  is  not  one  of  absolutely  higher  or  lower  tem- 
perature ;  for  the  animals  which  to  us  in  a  temperate  climate,  feel  cold 
(being  like  the  air  or  water,  colder  than  the  surface  of  our  bodies),  would 
in  an  external  temperature  of  ioo°  (37*8°  C.)  have  nearly  the  same  tempera- 
ture and  feel  hot  to  us.  The  real  difference  is  that  what  we  call  warm- 
blooded animals  (Birds  and  Mammalia),  have  a  certain  "  permanent  heat 
in  all  atmospheres, '"  while  the  temperature  of  the  others,  which  we  call 
cold-blooded,  is  ,:  variable  with  every  atmosphere."    (Hunter.) 

The  power  of  maintaining  a  uniform  temperature,  which  Mammalia  and 
Birds  possess,  is  combined  with  the  want  of  power  to  endure  such  changes 
of  body  temperature  as  are  harmless  to  the  other  classes :  and  when  their 
power  of  resisting  change  of  temperature  ceases,  they  suffer  serious  dis- 
turbance or  die. 

Sources  and  Mode  of  Production  of  Heat  in  the  Body. 
— The  heat  which  is  produced  in  the  body  arises  from  com- 
bustion, and  is  due  to  the  fact  that  the  oxygen  of  the  atmosphere 


thai'.  x.|  PBODUCTIOH    OP    HEAT. 

taken  into  th<  is  comb  ith  the  carbon  and  h j 

Any  changes  which  occur  in  the  protoplasm  of  tl 
suiting  in  an  exhibition  of  their  function,  is  attended  by 
tin-  evolution  of  heat  and  also  by  the  production  "f  carbonic  tu 
and  water  ;  and  the  more  active  the  changes,  the  greater  the  b  at 
produced  and  the  greater  the  amount  of  the  carbonic  acid  and  water 
formed.  But  in  order  that  the  protoplasm  may  perform  its  func- 
tion, the  waste  of  its  own-  »  structive  metabolism),  must  be 
repaired  by  the  supply  of  food  material,  and  therefore  for  the  produc- 
i  of  heat  it  is  necessary  to  supply  food.  In  the  tissues,  therefore, 
tw«>  pr  lessee  1  continually  going  on:  the  building  up  of  the 
protoplasm  from  the  t  nstructive  metabolism),  which  is  not 
accompanied  by  the  evolution  of  heat  but  possibly  by  the  ?•  -  , 
and  the  oxidation  of  the  protoplastic  materials,  resulting  in 
the  productioi  rgy,  by  which  heat  is  produced  and  carbonic 
acid  and  water  are  evolved.  Some  heat  will  also  he  generated 
in  the  combination  of  sulphur  and  phosphorus  with  oxygen,  but 
the  amount  thus  produced  is  but  small. 

It  is  not  necessary  to  assume  that  the  combustion  pro- 
se 3,  which  ultimately  issue  in  the  production  of  carbonic 
acid  and  water,  are  as  simple  as  the  bare  statement  «»f  the  fact 
might  seem  to  indicate.  But  complicated  as  the  vari<  3  stages 
of  combustion  may  be,  the  ultimate  result  is  as  simple  as  in 
ordinary  combustion  outside  the  body,  and  the  products  ..  the 
same.  .'  -  ime  amount  of  heat  will  be  evolved  in  the  union  of 
any  friven  quantities  of  carbon  and  oxygen,  and  of  hydrogen  and 
oxygen,  whether  the  combination  be  rapid  and  direct,  as  in 
ordinary  combustion,  or  slow  and  almost  imperceptible,  as  in  the 
chair.'-  which  occur  in  the  living  body.  And  *ince  the  heat  thus 
arising  will  be  distributed  wherever  the  blood  is  earned,  every  j 
of  the  body  will  be  heated  equally,  or  nearly  a 

This  the  ry.  that  the  maintenance  of  the   temperature  of  the 
living    body  depends  on  continual    chemical    change,   chiefly  by 
oxi.lnri-.il,   of  combustible   materials   existing   in  the  tissu 
long  stablished  by  the  demonstration  that  the  quantity  of 

and  hydrogen  which,  in  a  given  time,  unites  in  the  bt 
wit  _  sufficient    :  ant   for  the    amount   of  heat 

lerated  in  the  animal  within  the  same  time  :  an  amount  capable 
maintaining  the  temperature  of  the  body  at  from  98° — icoc  F. 

c  c 


386  ANIMAL    HEAT.  [<  hap.  x. 

(36-S° — 37*S:  C),   notwithstanding  a  large  loss  by  radiation1  and 

evaporation. 

It  should  be  remembered  that  heat  may  be  introduced  into 
the  body  by  means  of  warm  drinks  and  foods,  and,  again,  that 
it  is  possible  for  the  preliminary  digestive  changes  to  be  accom- 
panied by  the  evolution  of  heat. 

Chief  Heat-producing  Tissues.  —  The  chemical  changes 
which  produce  the  body-heat  appear  to  be  especially  active  in 
certain  tissues  : — (i),  In  the  Muscles,  which  form  so  large  a 
part  of  the  organism.  The  fact  that  the  manifestation  of 
muscular  energy  is  always  attended  by  the  evolution  of  heat 
and  the  production  of  carbonic  acid  has  been  demonstrated 
by  actual  experiment  :  and  when  not  actually  in  a  condition  of 
active  contraction,  a  metabolism,  not  so  active  but  still  actual, 
goes  on.  which  is  accompanied  by  the  manifestation  of  heat.  The 
total  amount  set  free  by  the  muscles,  therefore,  must  be  very 
great ;  and  it  has  been  calculated  that  even  neglecting  the  heat 
pr<  duced  by  the  quiet  metabolism  of  muscular  tissue,  the  amount 
of  heat  generated  by  muscular  activity  supplies  the  principal  part 
of  the  t"tal  heat  produced  within  the  body.  (2),  In  the 
Secreting  glands,  and  principally  in  the  liver  as  being  the  larg  si 
and  most  active.  It  lias  been  found  by  experiment  that  the 
blood  leaving  the  glands  is  &  nsiderably  warmer  than  that 
entering  them.  The  metabolism  in  the  glands  is  very  active  and, 
as  we  have  seen,  the  more  active  the  metabolism  the  greater 
the  heat  produced.  131.  In  tlve  Brain;  the  venous  blood 
having  a  higher  temperature  than  the  arterial.  It  must  lie 
remembered,  however,  that  although  the  organs  above  mentioned 
are  the  chief  heat-producing  parts  of  the  body,  all  living  tissues 
contribute  their  quota,  and  this  in  direct  proportion  t.>  their 
activity.  The  blood  itself  is  also  the  seat  of  metabolism,  and, 
therefore,  of  the  production  of  heat  :  but  the  share  which  it  takes 
in  this  respect,  apart  from  the  tissues  in  which  it  circulates,  is 
very  inconsideral  ile. 

Regulation  of  trie  Temperature  of  the  Human  Body.— 
The  average  temperature  of  the  body  is  maintained  under 
different  conditions  of  external  circumstances  by  mechanisms 
which  permit  of  (1)  variation  in  the  amount  of  heat  got  rid  of. 
and  (2)  variations  in  the  amount  of  heat  produced  or  introduced 


chap,  x.]  LOSS    OF    BEAT,  387 

into  the  body.     In  healthy  warm-blooded  animals  the  loss  and 
g   in  of  heat  are  so  nearly  balanced  one  by  the  other  that,  under 

all  ordinary  circui     "         5,  an   uniform   temperature,   within   * 
or  three      _      s,  is  preserve  1. 

I.  Methods  of  Variation  in  the  amount  of  Heat  got  rid 
of. — The   loss  of  heat  from  the  human  body  is  principally  regu- 
lated by  the   amount   lost  by  radiation  and   conduction  fi 
surface,  and  by  means  of  the  constant  evaporation  of  water  from 
the  same   part,   and    (2)   to  a    much    less       -_         from  the    air- 

38  _  -  :  iii  each  act  I  spiration,  heat  is  lost  to  a  greater  or 
stent  according  to  the  temperature  of  the  atmosphei 
unless  indeed  the  temperature  of  the  surrounding  air  exceed  that 
of  the  blood.  We  must  remember  too  that  all  food  and  drink 
which  enter  the  body  at  a  lower  temperature  than  itself  abstract 
a  small  measure  of  heat  :  while  the  mine  and  feces  which  leave 
the  body  at  about  its  own  temperature  are  also  means  by  which 
a  small  amount  is  I  st 

//  U  from  +'■■  >  vftfo  Body:  (lie Skin. — By  far 

the  nmst  important  loss  of  heat  from  the  body, — probably  70  or 
So  per  cent,  of  the  whole  amount,  is  that  which  takes  place  by 

liation,  conduction,  and  evaporation  from  the  skin.  The 
means  by  which  the  skin  is  able  to  act  as  one  of  the  m<  st 
important  organs  for  regulating  the  temperature  of  the  blood, 
are — 1 1  .  that  it  offers  a  large  surface  for  radiation,  conduction, 
and  evaporation  :  (2),  that  it  contains  a  larg       m     int     i  blood; 

.  that  the  quantity  of  blood  contained  in  it  is  the  greater 
under  those  circumstances  which  demand  a  loss  of  heat  from  the 
body,    and  For    the    circumstance    which    directly 

termines  the  quantity  of  blood  in  the  skin,  is  that  which 
_  rerns  the  supply  of  blood  to  all  the  tissues  and  organs  of  the 
body,  namely,  the  power  of  the  vaso-motor  nerves  to  cause  a 
ss  tension  of  the  muscular  element  in  the  walls  of 
the  arteries,  and.  in  correspondence  with  this,  a  lessening 
increase  1  >f  the  calibre  of  the  vessel,  accompanied  by  a  less  or 
greater  current  of  blood.  A  warm  or  hot  atmosphere-  its  on 
the  nerve  fibres  of  the  skin,  as  to  lead  them  to  cause  in  turn  a 
relaxation  of  the  muscular  fibre  of  the  blo<  -  ssels;  and,  as  a 
result,  the  skin  becomes  full-blooded,  hot,  and  sweating  :  and 
much  heat  is  lost.     With  a  low  temperature,  on  the  other  hand. 

c  c  2 


7g8  ANIMAL    HEAT.  [chap.  x. 

the  blood-vessels  shrink,  and  in  accordance  with  the  consequently 

diminished  blood-supply,  the  skin  becomes  pale.,  and  cold,  and 
dry  ;  and  no  doubt  a  similar  effect  may  be  produced  through  the 
vasomotor  centre  in  the  medulla  and  spinal  cord.  Thus,  by 
means  of  a  Belf-regulating  apparatus,  the  skin  becomes  the  most 
important  of  the  means  by  which  the  temperature  of  the  body  is 
regulated. 

In  connection  with  loss  of  heat  by  the  skin,  reference  has  been 
made  to  that  which  occurs  both  by  radiation  and  conduction, 
and  by  evaporation:  and  the  subject  of  animal  heat  lias  been 
considered  almost  solely  with  regard  to  the  ordinary  case  of  man 
living  in  a  medium  older  than  his  body,  and  therefore  losing- 
heat  in  all  the  ways  mentioned.  The  importance  of  the  means 
however,  adopted,  so  to  speak,  by  the  skin  for  regulating  the 
temperature  of  the  body,  will  depend  on  the  conditions  by  which 
it  is  surrounded;  an  inverse  proportion  existing  in  most  cases 
between  the  loss  by  radiation  and  conduction  on  the  one  hand, 
and  by  evaporation  on  the  other.  Indeed,  the  small  loss  of  heat 
bv  evaporation  in  cold  climates  may  go  far  to  compensate  for  the 
irreater  loss  bv  radiation:  as,  on  the  other  hand,  the  great 
amount  of  fluid  evaporated  in  hot  air  may  remove  nearly  as  much 
heat  as  is  commonly  lost  by  both  radiation  and  evaporation  in 
ordinary  temperatures;  and  thus,  it  is  possible  that  the  quantities 
of  heat  required  for  the  maintenance  of  an  uniform  proper  tempera- 
ture  in  various  climates  and  seasons  are  not  so  different  as  they, 
at  first  thought,  seem. 


Many  example  may  be  given  of  the  power  which  the  body  possesses  of 
resisting  tie  effects  af  a  l>><ih  temperature,  in  virtue  of  evaporation  from 
the  skin.  Blagden  and  others  supported  a  temperature  varying  between 
198"' — 2110  F.  (92"' — iooJ  C.)  in  dry  air  for  several  minutes;  and  in  a 
subsequent  experiment  he  remained  eight  minutes  in  a  temperature  of 
260"'  F.  (i26-5°  C).  "The  workmen  of  Sir  F.  Chantrey  were  accustomed  to 
enter  a  furnace,  in  which  his  moulds  were  dried,  whilst  the  floor  was  red-hot. 
and  a  thermometer  in  the  air  stood  at  3500  F.  (1778"  C.)  and  Chabert,  the 
fire-king,  was  in  the  habit  of  entering  an  oven  the  temperature  of  which  was 
from  400 3  to  6oo7:  F.  (2050— 3 15°  C.)    (Carpenter.) 

But  such  heats  are  not  tolerable  when  the  air  is  moist  as  well  as  hot, 
so  as  to  prevent  evaporation  from  the  body.  C.  James  states,  that  in 
the  vapour  baths  of  Nero  he  was  almost  suffocated  in  a  temperature  of 
1120  F.  (44*5D  C.  ),  while  in  the  caves  of  Testaccio,  in  which  the  air  is  dry,  he 
was   but   little  incommoded  by  a  temperature  of   1760  F.  (8o°  C).     In  the 


chap.  \.|  !  088    OP    HEAT.  jgg 

former,  evaporation  from  the  skin  was  impossible;  in  the  latter  it  waa 
abundant,  ami  the  layer oi  vapour  which  would  rise  from  all  the  surface  of 
the  body  would,  by  it-  very  slowly  conducting  |  fend  it  for  a 

a  the  full  action  .,t"  the  externa]  heat. 

(The  glandular  apparatus,   by   which   secretion   of*  fluid   from 
the  skin  is  effected,   will   be  considered    in  the  Section    on  the 

Skin.) 

The  ways  by  which  the  skin  may  lie  rendered    more  efficient   as 

oling-apparatus  by  exposure,  by  baths,  and  by  other  means 

which    man    instinctively   adopts   for   lowering   his    temperature 

when    uecessary,  are    too    well    known   to    need    more   than    to    be 

mentioned. 

Although  under  any  ordinary  circumstances,  the  external  application  of 
cold  only  temporarily  depresses  the  temperature  to  a  slight  extent,  it  is 
otherwise  in  cases  of  high  temperature  in  fever.  In  these  -  -  tepid 
hath  may  reduce  the  temperature  several  degrees,  and  the  effect  so  pro- 
duced lasts  in  some  cases  for  many  hours. 

Loss  of  Heat  from  tlu  Lungs. — As  a  means  for  lowering  the 
temperature,  the  lungs  and  air-passages  are  very  inferior  to  the 
skin:  although,  by  giving  heat  to  the  air  we  breathe,  they  stand 
next   to  the    skin    in   importance.      As    a    regulating  power,   the 

inferiority  is  still  more  marked.  The  air  which  is  expelled  from 
the  lungs  leaves  the  body  at  about  the  temperature  of  the  blood, 
and  is  always  saturated  with  moisture.  No  inverse  proportion, 
therefore,  exists  between  the  loss  of  heat  by  radiation  and  conduc- 
tion on  the  one  hand,  and  by  evaporation  on  the  other.  The 
colder  the  air.  for  example,  the  greater  will  be  the  loss  in  all  way* 
Neither  is  the  quantity  of  blood  which  is  exposed  to  the  cooling 
influence  of  the  air  diminished  or  increased,  s<>  far  as  is  known,  iu 
accordance  with  any  need  in  relation  to  temperature.  It  is  true 
that  by  varying  the  number  and  depth  of  the  respirations,  the 
quantity  of  heat  given  off  by  the  lungs  may  be  made,  to  some 
extent,  to  vary  also.  But  the  respiratory  passages,  while  they 
must  be  considered  important  means  by  which  heat  is  lest,  are 
altogether  subordinate,  in  the  power  of  regulating  the  temperature, 
to  the  skin. 

By  Clothing. — The  influence  of  external  coverings  for  the 
body  must  not  be  unnoticed.     In  warm-blooded  animals,  they  are 


3ro  ANIMAL    HEAT.  [chap.  x. 

always  adapted,  among  other  purposes,  to  the  maintenance  of 
uniform  temperature  ;  and  man  adapts  for  himself  such  as  are, 
for  the  same  purpose,  fitted  to  the  various  climates  to  which  he  is 
exposed.  By  their  means,  and  by  his  command  over  food  and 
fire,  he  maintains  his  temperature  on  all  accessible  parts  of  the 
surface  of  the  earth. 

II.  Methods  of  Variation  in  the  Amount  of  Heat  Pro- 
duced.— It  may  seem  to  have  been  assumed,  in  the  foreg<  dug 
pages,  that  the  only  regulating  apparatus  for  temperature 
required  by  the  human  body  is  one  that  shall,  more  or  less, 
produce  a  cooling  effect  ;  and  as  if  the  amount  of  heat  produced 
were  always,  therefore,  in  excess  of  that  which  is  required.  Such 
an  assumption  would  be  incorrect.  We  have  the  power  of  regu- 
lating the  production  of  heat,  as  well  as  its  loss. 

(a)  By  Regulating  the  Quantity  and  Quality  of  the  Food  taken. 

In  food   we   have   a  means  for  elevating  our  temperature.      It 

is  the  fuel,  indeed,  on  which  animal  heat  ultimately  depends 
altogether.  Thus,  when  more  heat  is  wanted,  we  instinctively 
take  more  food,  and  take  such  kinds  of  it  as  are  good  for  com- 
bustion :  while  every-day  experience  shows  the  different  power  of 
resisting  cold  possessed,  respectively,  by  the  well-fed  and  by  the 
starved.  In  northern  regions,  again,  and  in  the  colder  seasons  of 
more  southern  climes,  the  quantity  of  food  consumed  is  (speaking 
very  generally)  greater  than  that  consumed  by  the  same  men  or 
animals  in  opposite  conditions  of  climate  and  season.  And  the 
food  which  appears  naturally  adapted  to  the  inhabitants  of  the 
coldest  climates,  such  as  the  several  fatty  and  oily  substances, 
abounds  in  carbon  and  hydrogen,  and  is  fitted  to  combine  with 
the  large  quantities  of  oxygen  which,  breathing  cold  dense  air,  they 
absorb  from  their  lungs. 

(b.)  By  Exercise. — In  exercise,  we  have  an  important  means 
of  raising  the  temperature  of  our  bodies  (p.  383). 

(c.)  By  Influence  of  the  Kercous  System. — The  influence  of  the 
nervous  svstem  in  modifying  the  production  of  heat  must  be  very 
important,  as  upon  nervous  influence  depends  the  amount  of  the 
metabolism  of  the  tissues.  The  experiments  and  observations 
which  best  illustrate  it  are  those  showing,  first,  that  when  the 
supply  of  nervous  influence  to  a  part  is  cut  off,  the  temperature 
of  that  part  falls  below  its  ordinary  degree  ;  and,  secondly,  that 


<  hap.  x.l      REGULATION  OF  TEMPERATURE. 


391 


when  death  is  caused  bj  severe  injury  to,  or  removal  of,  the 
nervous  centres,  the  temperature  <>f  the  body  rapidh  falls,  even 
though  artificial  respiration  be  performed,  the  circulation  main- 
tained, and  to  all  appearance  the  ordinary  chemical  changes  of 
the  body  be  completely  effected.  It  has  been  repeatedly 
noticed,  that  after  division  of  the  nerves  of  a  limb  its  tempe- 
rature lulls  ;  and  this  diminution  of  beat  has  been  remarked 
still  more  plainly  in  Limbs  deprived  of  nervous  influence  by 
paralysis. 

With  equal  certainty,  though  less  definitely,  the  influence  of 
the  nervous  system  on  the  production  of  heat,  is  shown  in  the 
rapid  and  momentary  increase  of  temperature,  sometimes  general, 
at  other  times  quite  local,  which  is  observed  in  states  of  nervous 
excitement;  in  the  general  increase  of  warmth  of  the  body, 
sometimes  amounting  to  perspiration,  which  is  excited  by  passions 
of  the  mind  ;  in  the  sudden  rush  of  heat  to  the  face,  which  is 
not  a  mere  sensation;  and  in  the  equally  rapid  diminution  of 
temperature  in  the  depressing  passions.  But  none  of  these 
instances  suffice  to  prove  that  heat  is  generated  by  mere  nervous 
action,  independent  of  any  chemical  change;  all  are  explicable, 
on  the  supposition  that  the  nervous  system  alters,  by  its  power 
of  controlling  the  calibre  of  the  blood-vessels,  the  quantity 
of  blood  supplied  to  a  part  ;  while  any  influence  which  the 
nervous  system  may  have  in  the  production  of  heat,  apart  from 
this  influence  on  the  blood-vessels,  is  an  indirect  one,  and  is 
derived  from  its  power  of  causing  such  nutritive  change  in  the 
tissues  as  may,  by  involving  the  necessity  of  chemical  action, 
involve  the  production  of  heat. 

Inhibitory  heat-centre. — Whether  a  centre  exists  which  regulates 
the  production  of  heat  in  warm-blooded  animals,  is  still  unde- 
cided. Experiments  have  shown  that  exposure  to  cold  at  once 
increases  the  oxygen  taken  in,  and  the  carbonic  acid  given  out, 
indicating  an  increase  in  the  activity  of  the  metabolism  of  the 
tissues,  but  that  in  animals  poisoned  by  urari,  exposure  to  cold 
diminishes  both  the  metabolism  and  the  temperature,  and  warm- 
blooded animals  then  re-act  to  variations  of  the  external  tempe- 
rature just  in  the  same  way  as  cold-blooded.  These  experiments 
seem  to  suggest  that  there  is  a  centre,  to  which,  under  normal 
circumstances,  the  impression  of  cold  is  conveyed,  and  from  which 


392  ANIMAL    HEAT.  [chap.  X. 

by  efferent  nerves  impulses  pass  to  the  muscles,  whereby  an 
increased  metabolism  is  induced,  and  so  an  increased  amount  of 
heat  is  generated.  The  centre  is  probably  situated  above  the 
medulla.  Thus  in  urarised  animals,  as  the  nerves  to  the  muscles, 
the  metabolism  of  which  is  so  important  in  the  production  of 
heat,  are  paralyzed,  efferent  impulses  from  the  centre  cannot 
induce  the  necessary  metabolism  for  the  production  of  heat,  even 
though  afferent  impulses  from  the  skin,  stimulated  by  the  altera- 
tion of  temperature,  have  conveyed  to  it  the  necessity  of  altering 
the  amount  of  heat  to  be  produced.  The  same  effect  is  produced 
when  the  medulla  is  cut. 

Influence  of  Extreme  Heat  and  Cold. — In  connection  with 
the  regulation  of  animal  temperature,  and  its  maintenance  in 
health  at  the  normal  height,  may  be  noted  the  result  of  circum- 
stances too  powerful,  either  in  raising  or  lowering  the  heat  of 
the  body,  to  be  controlled  by  the  proper  regulating  apparatus. 
Walther  found  that  rabbits  and  dogs,  when  tied  to  a  board  and 
exposed  to  a  hot  sun.  reached  a  temperature  of  114*8°  F.,  and 
then  died.  Cases  of  sunstroke  furnish  us  with  several  examples 
in  the  case  of  man  :  for  it  would  seem  that  here  death  ensues 
chiefly  or  solely  from  elevation  of  the  temperature.  In  many 
febrile  diseases  the  immediate  cause  of  death  appears  to  be  the 
elevation  of  the  temperature  to  a  point  inconsistent  with  the 
continuance  of  life. 

The  effect  <»f  mere  loss  of  bodih-  temperature  in  man  is  less  well 
known  than  the  effect  of  heat.  From  experiments  by  Walther,  it 
appears  that  rabbits  can  lie  cooled  down  to  48°  F.  (8"o/  C),  before 
they  die,  if  artificial  respiration  be  kept  up.  Cooled  down  to 
640  F.  ( 1 7'S"  C),  they  cannot  recover  unless  external  warmth  be 
applied  together  with  the  employment  of  artificial  respiration. 
Babbits  net  cooled  below  77°  F.  (250  C.)  recover  by  external 
warmth  alone. 


<  hap.  xi.  1  SECRETION.  303 


rilAlTEK    XI. 

SECRETION. 

Secretion    is  the   process   by    which   materials   arc   separated 
from  the  blood,  and  from  the  organs  in  which  they  are  formed, 
for   the    purpose   either   <>f  serving   Borne    ulterior   office  in   the 
economy,  or  of  being  discharged   from  the  body  as   useless 
injurious.      In  the  former  case,  the  separated  materials  are  termed 

•etions  ;  in  the  latter,  they  arc  termed  excretions. 

Most  of  the  secretions  consist  of  Bubstances  which,  probably,  do 
DOt  pre-exist  in  the  same  form  in  the  blood,  but  require  special 
organs  and  a  process  of  elaboration  for  their  formation,  e.g.,  the 
liver  for  the  formation  of  bile,  the  mammary  gland  for  the  forma- 
tion of  milk.  The  excretions,  on  the  other  hand,  commonly  or 
chiefly  consist  of  substances  which  exist  ready-formed  in  the 
blood,  and  are  merely  abstracted  therefrom.  If  from  any  cause. 
such  as  extensive  disease  or  extirpation  of  an  excretory  organ, 
the  separation  of  an  excretion  is  prevented,  and  an  accumulation 
of  it  in  the  blood  ensues,  it  frequently  escapes  through  other 
organs,  and  may  be  detected  in  various  fluids  of  the  body.  But 
this  is  never  the  case  with  secretions:  at  least  with  those  that 
are  most  elaborated;  for  after  the  removal  of  the  special  orpins 
by  which  any  of  them  is  elaborated,  it  is  no  longer  formed. 
-  sometimes  occur  in  which  the  secretion  continues  to  be 
formed  by  the  natural  organ,  but  not  being  able  to  escape  to- 
wards the  exterior,  on  account  of  some  obstruction,  is  re-absorbed 
into  the  blood,  and  afterwards  discharged  from  it  by  exudation  in 
other  ways;  but  these  arc  not  instances  of  true  vicarious  secre- 
tion, and  must  not  be  thus  regarded. 

These  circumstances,  and  their  final  destination,  are.  however, 
the  only  particulars  in  which  secretions  and  excretions  can  be 
distinguished  ;  for,  in  general,  the  structure  of  the  parts  engaged 
in  eliminating  excretions  is  as  complex  as  that  of  the  parts  con- 
cerned in  the  formation  of  secretions.  And  since  the  differences  of 
the  two  proa  8S<  -  of  separation,  corresponding  with  those  in  the 
several   purposes  and   destinations  of  the  fluids,  are  not  yet  ascer- 


394 


SECRETION. 


[CHAP.  XI. 


tained,  it  will  be  sufficient  to  speak  in  general  terms  of  the  process 
of  separation  or  secretion. 

Every  secreting  apparatus  possesses,  as  essential  parts  of  its 
structure,  a  simple  and  almost  textureless  membrane,  named 
the  primary  or  basement-membrane  ;  certain  cells  ;  and  blood-vessels. 
These  three  structural  elements  are  arranged  together  in  various 
wavs:  but  all  the  varieties  may  be  classed  under  one  or  other  of 
two  principal  divisions,  namely,  membranes  and  glands. 


Organs  and  Tissues  of  Secretion. 

The  principal  secreting  membranes  are  (i)  the  Serous  and 
Synovial  membranes;  (2)  the  Mucous  membranes ;  (3)  the  Mam- 
mary gland  ;  (4)  the  Lachrymal  gland  ;  and  (5)  the  Skin. 

(1)  Serous  Membranes. — The  serous  membranes  are  espe- 
cially- distinguished  by  the  characters  of  the  endothelium  covering 

their  free  surface  :  it 
always  consists  of  a 
single  layer  of  polygonal 
cells.  The  ground  sub- 
stance of  most  serous 
membranes  consists  of 
connective  -  tissue  cor- 
puscles of  various  forms 
lying  in  the  branching 
spaces  which  constitute 
the  "  lymph  canalicular 
system"  (p.  363),  and 
interwoven  with  bundles 
of  white  fibrous  tissue, 
and  numerous  delicate 
elastic  fibrillse,  together 
with  blood-  vessels, 
nerves,  and  lymphatics. 
In  relation  to  the  pro- 
cess of  secretion,  the 
layer  of  connective 
tissue  serves  as  a  ground-work  for  the  ramification  of  blood-vessels, 
lymphatics,  and  nerves.  But  in  its  usual  form  it  is  absent  in 
some  instances,    as   in   the  arachnoid   covering  the    dura  mater, 


Fig.  210. — Section  of  synovial  membrane,  a,  endothelial 
covering  of  elevations  of  the  membrane  :  b,  sub- 
serous tissue  containing  fat  and  blood-vessels ;  <■, 
Ligament  covered  bv  the  synovial  membrane. 

(Cadiat.; 


chap.  xi.  |  SEBOUS    FLUID.  395 

and  in  the  Interior  of  the  ventricles  of  the  brain.  The  primary 
membrane  and  epithelium  are  always  present,  an  1  are  concerned 
in  the  formation  of  the  fluid  by  which  tin-  free  surface  of  the 
membrane  is  moistened. 

Scnms  membranes  are  of  two  principal  kinds  ;  [*/.  'rim-,' wind, 
line  visceral  cavities,  —-the  arachnoid,  pericardium,  pleural,  perito- 
neum9  and  tunica  vaginaies.  2nd.  The  synovial  membranes  lining  tin- 
joints,  and  the  sheaths  of  tendons  and  ligaments,  with  which,  also, 
arc  usually  included  the. synovial  bursi e,  or  bursasmuco9cey  whetherthese 
be  subcutaneous,  or  situated  beneath  tendons  that  glide  over  bones. 

The  serous  membranes  form  closed  sacs,  and  exist  wherever 
the  tree  surfaces  of  viscera  come  into  contact  with  each  other  or 
lie  in  cavities  unattached  to  surrounding  parts.  The  viscera 
invested  by  a  serous  membrane  are,  as  it  were,  pressed  into  the 
shut  sac  which  it  forms,  carrying  before  them  a  portion  of  the 
membrane,  which  serves  as  their  investment.  To  the  law  that 
serous  membranes  form  shut  sacs,  there  is,  in  the  human  subject, 
one  exception,  viz. :  the  opening  of  the  Fallopian  tubes  into  the 
abdominal  cavity, — an  arrangement  which  exists  in  man  and  all 
Vertebrata,  with  the  exception  of  a  few  fishes. 

Functions. — The  principal  purpose  of  the  serous  and  synovial 
membranes  is  to  furnish  a  smooth,  moist  surface,  to  facilitate  the 
movements  of  the  invested  organ,  and  to  prevent  the  injurious 
effects  of  friction.  This  purpose  is  especially  manifested  in  joints, 
in  which  free  and  extensive  movements  take  place  ;  and  in  the 
stomach  and  intestines,  which,  from  the  varying  quantity  and 
movements  of  their  contents,  are  in  almost  constant  motion  upon 
one  another  and  the  walls  of  the  abdomen. 

Serous  Fluid. — The  fluid  secreted  from  the  free  surface  of  the 
serous  membranes  is,  in  health,  rarely  more  than  sufficient  to  ensure 
the  maintenance  of  their  moisture.  The  opposed  surfaces  of  each 
serous  sac  are  at  every  point  in  contact  with  each  other.  After  death, 
a  larger  quantity  of  fluid  is  usually  found  in  each  serous  sac  ;  but 
this,  if  not  the  product  of  manifest  disease,  is  probably  such  as 
has  transuded  after  death,  or  in  the  last  hours  of  life.  An  excess 
of  such  fluid  in  any  of  the  serous  sacs  constitutes  dropsy  of  the  sac. 

The  fluid  naturally  secreted  by  the  serous  membranes  appears 
to  be  identical,  in  general  and  chemical  characters,  with  the 
serum   of  the  blood,  or  with    very  dilute  liquor  sanguinis.      It   is 


396       '  SECRETION.  [chap.  xi. 

of  a  pale  yellow  or  straw-colour,  slightly  viscid,  alkaline,  mid,  on 
account  of  the  presence  of  albumen,  eoagulable  by  heat.  This 
similarity  of  the  serous  fluid  to  the  liquid  part  of  blood,  and  to 
the  fluid  with  which  most  animal  tissues  are  moistened,  renders  it 
probable  that  it  is,  in  great  measure,  separated  by  simple  transu- 
dation, through  the  walls  of  the  blood-vessels.  The  probability  is 
increased  by  the  fact  that,  in  jaundice,  the  fluid  in  the  serous 
sacs  is,  equally  with  the  serum  of  the  blood,  coloured  with  the 
bile.  But  there  is  reason  for  supposing  that  the  fluid  of  the 
cerebral  ventricles  and  of  the  arachnoid  sac  are  exceptions  to 
this  rule  :  for  they  differ  from  the  fluids  of  the  other  serous  sacs 
not  only  in  being  pellucid,  colourless,  and  of  much  less  specific 
gravity,  but  in  that  they  seldom  receive  the  tinge  of  bile  when 
present  in  the  blood,  and  are  not  coloured  by  madder,  or  other 
similar  substances  introduced  abundantly  into  the  blood. 

Synovial  Fluid  :  Synovia. — It  is  also  probable  that  the 
formation  of  synovial  fluid  is  a  process  of  more  genuine  and  elabo- 
rate secretion,  by  means  of  the  epithelial  cells  on  the  surface  of 
the  membrane,  and  especially  of  those  which  are  accumulated  on  the 
edges  and  processes  of  the  synovial  fringes;  for,  in  its  peculiar  density, 
viscidity,  and  abundance  of  albumin,  synovia  differs  alike  from  the 
serum  of  blood  and  from  the  fluid  of  any  of  the  serous  cavities. 

(2)  Mucous  Membranes.  —  The  mucous  membranes  line  all 
those  passages  by  which  internal  parts  communicate  with  the 
exterior,  and  by  which  either  matters  are  eliminated  from  the 
body  or  foreign  substances  taken  into  it.  They  are  soft  and 
velvety,  and  extremely  vascular.  The  external  surfaces  of  mucous 
membranes  are  attached  to  various  other  tissues ;  in  the  tongue, 
for  example,  to  muscle  ;  on  cartilaginous  parts,  to  perichondrium; 
in  the  cells  of  the  ethmoid  bone,  in  the  frontal  and  sphenoidal 
sinuses,  as  well  as  in  the  tympanum,  to  periosteum  ;  in  the 
intestinal  canal,  it  is  connected  with  a  firm  submucous  mem- 
brane, which  on  its  exterior  gives  attachment  to  the  fibres  of 
the  muscular  coat.  The  mucous  membranes  line  certain  prin- 
cipal tracts — Gastro-Pulmonaiy  and  Genito-Urinary  ;  the  former 
being  subdivided  into  the  Digestive  and  Respiratory  tracts. 
1.  The  Digestive  tract  commences  in  the  cavity  of  the  mouth. 
from  which  prolongations  pass  into  the  ducts  of  the  salivary 
glands.     From  the  mouth  it  passes  through  the  fauces,  pharynx, 


i  ii  u\  si.]  MUCOUS    MEMBB  V.NES  307 

and  oesophagus,  to  the  stomach,  and  is  thenco  continued  along 
the  whole  tract  of  the  intestinal  canal  to  the  termination  of  the 
rectum,  being  in  its  course  arranged  in  the  various  folds  and 
depressions  already  described,  and  prolonged  into  the  ducts  of  the 
intestinal  glands,  the  pancreas  and  liver,  and  into  the  gall-bladder. 
2.  The  Respiratory  tract  includes  the  mucous  membrane  lining 
the  cavity  of  the  nose,  and  the  various  sinuses  communicating 
with  it,  the  Lachrymal  canal  and  sac,  the  conjunctiva  of  the  eye 
and  eyelids,  and  the  prolongation  which  passes  along  the  Eusta- 
chian tubes  and  lines  the  tympanum  and  the  inner  surface  of  the 
membrana  tympani.  Crossing  the  pharynx,  and  lining  that  part 
of  it  which  is  above  the  soft  palate,  the  respiratory  tract  leads 
into  tin1  glottis,  whence  it  is  continued,  through  the  larynx  and 
trachea,  t<>  the  bronchi  and  their  divisions,  which  it  lines  as  far  as 
the  branches  of  about  gL  of  an  inch  in  diameter,  and  continuous 
with  it  is  a  layer  of  delicate  epithelial  membrane  which  extends 
into  the  pulmonary  cells.  3.  The  Genito-urinary  tract,  which 
lines  the  whole  of  the  urinary  passages,  from  their  external  orifice 
to  the  termination  of  the  fcubuli  uriniferi  of  the  kidneys,  extends 
also  into  the  organs  of  generation  in  both  sexes,  and  into  the 
ducts  of  the  glands  connected  with  them;  and  in  the  female 
becomes  continuous  with  the  serous  membrane  of  the  abdomen  at 
the  fimbriae  of  the  Fallopian  tubes. 

Structure. — Along  each  of  the  above  tracts,  and  in  different 
portions  of  each  of  them,  the  mucous  membrane  presents  certain 
structural  peculiarities  adapted  to  the  functions  which  each  part 
has  to  discharge;  yet  in  some  essential  characters  mucous  mem- 
brane is  the  same,  from  whatever  part  it  is  obtained.  In  all  the 
principal  and  larger  parts  of  the  several  tracts,  it  presents,  as  just 
remarked,  an  external  layer  of  epithelium,  situated  upon  basement 
membrane,  and  beneath  this,  a  stratum  of  vascular  tissue  of  vari- 
able thickness,  containing  lymphatic  vessels  and  nerves  which  in 
different  cases  presents  either  out-growths  in  the  form  of  papillae 
and  villi,  or  depressions  or  involutions  in  the  form  of  glands.  But 
in  the  prolongations  of  the  tracts,  where  they  pass  into  gland- 
ducts,  these  constituents  are  reduced  in  the  finest  branches  of  the 
ducts  to  the  epithelium,  the  primary  or  basement-membrane,  and 
the  capillary  blood-vessels  spread  over  the  outer  surface  of  the 
latter  in  a  single  layer. 


398  SECRETION.  [chap.  xr. 

The  primary  or  basement-membrane  is  a  thin  transparent  layer, 
simple,  homogeneous,  or  composed  of  endothelial  cells.  In  the 
minuter  divisions  of  the  mucous  membranes,  and  in  the  ducts  of 
glands,  it  is  the  layer  continuous  and  correspondent  with  this 
basement-membrane  that  forms  the  proper  walls  of  the  tubes. 
The  cells  also  which,  lining  the  larger  and  coarser  mucous  mem- 
branes, constitute  their  epithelium,  are  continuous  with,  and  often 
similar  to  those  which,  lining  the  gland-ducts,  are  called  gland- 
cells.  No  certain  distinction  can  be  drawn  between  the  epithelium- 
cells  of  mucous  membranes  and  gland-cells.  It  thus  appears,  that 
the  tissues  essential  to  the  production  of  a  secretion  are,  in  their 
simplest  form,  a  membrane,  having  on  one  surface  blood-vessels, 
and  on  the  other  a  layer  of  cells,  which  may  be  called  either 
epithelium-cells  or  gland-cells. 

Mucous  Fluid :  Mucus. — From  all  mucous  membranes  there 
is  secreted  either  from  the  surface  or  from  certain  special  glands, 
or  from  both,  a  more  or  less  viscid,  greyish,  or  semi-transparent 
fluid,  of  alkaline  reaction  and  high  specific  gravity,  named  mucus. 
It  mixes  imperfectly  with  water,  but,  rapidly  absorbing  liquid,  it 
swells  considerably  when  water  is  added.  Under  the  microscope 
it  is  found  to  contain  epithelium  and  leucocytes.  It  is  found  to  be 
made  up,  chemically,  of  a  nitrogenous  principle  called  mucin  which 
forms  its  chief  bulk,  of  a  little  albumen,  of  salts  chiefly  chlorides 
and  phosphates,  and  water  with  traces  of  fats  and  extractives. 

Secreting  Glands.— The  structure  of  the  elementary  portions 
of  a  secreting  apparatus,  namely  epithelium,  simple  membrane, 
and  blood-vessels  having  been  alread}'  described  in  this  and 
previous  chapters,  we  may  proceed  to  consider  the  manner  in 
which  they  are  arranged  to  form  the  varieties  of  secretin;/  glands. 

The  secreting  glands  are  the  organs  to  which  the  function  of 
secretion  is  more  especially  ascribed ;  for  they  appear  to  be 
occupied  with  it  alone.  They  present,  amid  manifold  diversities 
of  form  and  composition,  a  general  plan  of  structure,  by  which 
they  arc  distinguished  from  all  other  textures  of  the  body  ;  espe- 
cially, all  contain,  and  appear  constructed  with  particular  regard 
to,  the  arrangement  of  the  cells,  which,  as  already  expressed,  both 
line  their  tubes  or  cavities  as  an  epithelium,  and  elaborate,  as 
secreting  cells,  the  substances  to  be  discharged  from  them.  Glands 
arc  provided  also  with  lymphatic  vessels  and  nerves.     The  distri- 


chap.  >.;.  I  SECRETING    GLAXDS. 


399 


bution  of  the  former  is  not  peculiar,  and  need  not  be  here  con- 
sidered. Nerve-fibres  are  distributed  both  to  the  blood-vessels  of 
the  gland  and  to  its  ducts  ;  and,  in  some  glands,  to  the  secreting 

cells  also  (p.   282). 

Varieties. — 1.  The  simple  tubule,  or  tubular  gland  (a,  fig.  220), 
examples  of  which  are  furnished  by  some  mucous  glands,  the 
follicles  of  Lieberkiihn  (fig.  186),  and  the  tubular  glands  of  the 
stomach.  These  appear  to  be  simple  tubular  depressions  of  the 
mucous  membrane,  the  wall  of  which  is  formed  of  primary  mem- 
brane, and  is  lined  with  secreting  cells  arranged  as  an  epithelium. 
To  the  same  class  may  be  referred  the  elongated  and  tortuous 
sudoriferous  glands. 

The  compound  tubular  glands  (i>,  fig.  220)  form  another  division. 
These  consist  of  main  gland-tubes,  which  divide  and  sub-divide. 
Each  gland  may  consist  of  the  subdivisions  of  one  or  more  main 
tubes.  The  ultimate  sub-divisions  of  the  tubes  are  generally 
highly  convoluted.  They  are  formed  of  a  basement-membrane, 
lined  by  epithelium  of  various  forms.  The  larger  tubes  may  have 
an  outside  coating  of  fibrous,  areolar,  or  muscular  tissue.  The 
kidney,  testis,  salivary  glands,  pancreas,  Brunner's  glands  with 
the  lachrymal  and  mammary  glands,  and  some  mucous  glands  are 
examples  of  this  type,  but  present  more  or  less  marked  variations 
among  themselves. 

-.  The  aggregate  or  racemose  glands,  in  which  a  number  of 
vesicles  or  acini  are  arranged  in  groups  or  lobules  (0,  fig.  220). 
The  Meibomian  follicles  arc  examples  of  this  kind  of  gland. 

These  various  organs  differ  from  each  other  only  in  secondary 
points  of  structure ;  such  as,  chiefly,  the  arrangement  of  their 
excretory  ducts,  the  grouping  of  the  acini  and  lobules,  their  con- 
nection by  areolar  tissue,  and  supply  of  blood  vessels.  The  acini 
commonly  appear  to  be  formed  by  a  kind  of  fusion  of  the  walls  of 
several  vesicles,  which  thus  combine  t<>  form  one  cavity  lined  or 
tilled  with  secreting  cells  which  also  occupy  recesses  from  the  main 

vity.  The  smallest  branches  of  the  gland-ducts  sometimes  open 
into  the  centres  of  these  cavities  ;  sometimes  the  acini  are  clustered 
round  the  extremities,  or  by  the  sides  of  the  ducts  :  but,  whatever 

ondary  arrangement  there  may  be,  nil  have  the  same  essential 
character  of  rounded  groups  of  vesicles  containing  gland-cells, 
and  opening  by  a  common  central  cavity  into  minute  ducts,  which 


400 


SECRETION, 


[CHAP.  XI. 


ducts  in  the  large  glands  converge  and  unite  to  form  larger  and 
larger  branches,  and  at  length  by  one  common  trunk,  open  on  a 
free  surface  of  membrane. 


1   a^j    SSSfP^ 


fig.  220. — Plans  of ' exU  ecre&ng  membrane  by  inversion  or  formoft 

A.  -imple  gland*,  viz.  .<-/,  straight  tub*-  :   h,  sac  ;  ;,  coiled  tube.    B,  multilocular  er. 
i-,  of  tubular  form  :  Jar.      I  .  i  i  saccular  compound   gland;   rn, 

entire  eland,  showing  branched   duct  and  lobular  structure  ;    «.  a  lobule,  detached 
with  0,  branch  of  duct  proceeding  from  it.     L>,  compound  tubular  gland  (Sharpey  . 

Among  these  varieties  of  structure,  all  the  secreting  glands  arc- 
alike  in  some  essential  points,  besides  those  which  they  have 
in  common  -with  all  truly  secreting  structures.  They  agree  in 
presenting  a  large  extent  of  secreting  surface  within  a  compara- 
tively small  space ;  in  the  circumstance  that  while  one  end  of  the 


-mm'.  xi.]  PE0CE8S    OF    SECRETION.  401 

gland-dud  opens  <»n  a  free  surface,  the  opposite  cud  is  always 
closed,  having  do  direct  communication  with  blood  vessels,  or  any 
other  canal  ;  and  in  an  uniform  arrangement  of  capillary  blood- 
vessels, ramifying  and  forming  a  network  around  the  walls  and  in 
the  interstices  of  the  ducts  and  acini. 

Process  of  Secretion. — In  secretion    two    distinct    proc< 
are  concerned  which  may  be  spoken  of  as  I.   Physical)  and  II. 
Chemical, 

1.  Physical  />/-o<rsses. — These  are  such  as  can  be  closely  imitated 
in  the  laboratory,  inasmuch  as  they  consist  in  the  operation  of 
well-known  physical  laws  :  they  are — 

(a)  Filtration.      (6)  Diffusion. 

(")  Filtration  is  simply  the  passage  of  a  fluid  through  a  porous 
membrane  under  the  influence  of  pressure.  If  two  fluids  be 
separated  by  a  porous  membrane,  and  the  pressure  on  one  side 
is  greater  than  on  the  other,  it  is  evident  that  in  the  absence  of 
counteracting  osmotic  influences  (see  below)  there  will  be  a 
filtration  through  the  membrane  until  the  pressure  on  the  two 
sides  is  equalized.  Of  course  there  may  only  be  fluid  on  one  side 
of  the  membrane,  as  in  the  ordinary  process  of  filtering  through 
blotting-paper,  and  then  the  filtration  will  continue  as  long  as  the 
pressure  (in  this  case,  the  weight  of  the  fluid)  is  sufficient  to  force 
it  through  the  pores  of  the  filter.  The  necessary  inequality  of 
pressure  may  be  obtained  either  by  diminishing  it  on  one  'side,  as  in 
the  case  of  cupping ;  or  increasing  it  on  the  other,  as  in  the  case  of 
the  increased  blood-pressure  and  consequent  increased  flow  of  urine 
resulting  from  copious  drinking.  By  filtration,  not  merely  water, 
but  various  salts  in  solution  may  transude  from  the  blood  vessels. 
It  seems  probable  that  some  fluids,  such  as  the  secretions  of  serous 
membranes,  are  simply  exudations  or  oozings  (filtration)  from  the 
blood-vessels,  whose  qualities  are  determined  by  those  of  the 
liquor  sanguinis,  while  the  quantities  are  liable  to  variation,  and 
are  chiefly  dependent  upon  the  blood-pressure. 

(b)  Diffusion  is  the  passage  of  fluids  through  a  moist  animal 
membrane  independent  of  pressure,  and  sometimes  actually  in 
opposition  to  it.  There  must  always  be  in  this  process  two 
fluids  differing  in  composition,  one  or  both  possessing  an  affinity 
for  the  intervening  membrane,  and  the  fluids  capable  of  b2ing 
mixed  one  with  the  other  ;  the  osmotic  current  continuing  in  each 

D   D 


402  SECRETIOX.  [chap.  xr. 

direction  (when  both  fluids  have  an  affinity  for  the  membrane)  until 
the  chemical  composition  of  the  fluid  on  each  side  of  the  septum 
becomes  the  same. 

2.  Chemical  processes. — These  constitute  the  process  of  secretion 
properly  so  called  as  distinguished  from  mere  transudation  spoken 
of  above.  In  the  chemical  process  of  secretion  various  materials 
which  do  not  exist  as  such  in  the  blood  are  elaborated  by  the 
agency  of  the  gland-cells  from  the  blood,  or,  to  speak  more  accu- 
rately, from  the  plasma  which  exudes  from  the  blood-vessels  into 
the  interstices  of  the  gland-textures. 

The  best  evidence  for  this  view  is  :  ist.  That  cells  and  nuclei 
are  constituents  of  all  glands,  however  diverse  their  outer  forms 
and  other  characters,  and  are  in  all  glands  placed  on  the  surface 
or  in  the  cavity  whence  the  secretion  is  poured.  2nd.  That 
many  secretions  which  are  visible  with  the  microscope  may  be 
seen  in  the  cells  of  their  glands  before  they  are  discharged. 
Thus,  bile  may  be  often  discerned  by  its  yellow  tinge  in  the 
gland-cells  of  the  liver ;  spermatozoids  in  the  cells  of  the  tubules  of 
the  testicles ;  granules  of  uric  acid  in  those  of  the  kidneys  (of  fish) ; 
fatty  particles,  like  those  of  milk,  in  the  cells  of  the  mammary  gland. 
Secreting  cells,  like  the  cells  or  other  elements  of  any  other 
organ,  appear  to  develop,  grow,  and  attain  their  individual  per- 
fection by  appropriating  nutriment  from  the  fluid  exuded  by 
adjacent  blood-vessels  and  elaborating  it,  so  that  it  shall  form  part 
of  their  own  substance.  In  this  perfected  state,  the  cells  subsist 
for  some  brief  time,  and  when  that  period  is  over  they  appear  to 
dissolve,  wholly  or  in  part,  and  yield  their  contents  to  the  peculiar 
material  of  the  secretion.  And  this  appears  to  be  the  case  in  every 
part  of  the  gland  that  contains  the  appropriate  gland-cells  ;  there- 
fore not  in  the  extremities  of  the  ducts  or  in  the  acini  alone,  but 
in  great  part  of  their  length. 

"We  have  described  elsewhere  the  changes  which  have  been 
noticed  from  actual  experiment  in  the  cell's  of  the  salivary  glands, 
pancreas,  and  peptic  gland  (pp.  2S9,  321,  329). 

Discharge  of  Secretions  from  glands  may  either  take  place 
as  soon  as  they  are  formed ;  or  the  secretion  may  be  long  retained 
within  the  gland  or  its  ducts.  The  former  is  the  case  witli  the 
sweat  glands.  But  the  secretions  of  those  glands  whose  activity 
of  function  is  only  occasional  are  usually  retained  in  the  cells  in 


xi.]    CIRCUMSTANCES    IXKI.rKV  I.v-  RETION. 


403 


an  ondeveloped  form  during  ti  Is  of  the  gland's  inaction. 

And  there  arc  glands  which   are   like   both  these   •  such 

as   the   lachrymal,    which   constantly  small  portions   of 

fluid,  and  on  oc    -    os  oi    gn    I  titement  discharge  it  more 

abundantly. 

When  discharged  into  the  ducts,  the  further  course  of  secre- 
tious  is  affected  partly  by  the  pressure  from  behind  ;  the  fresh 
quantities  of  secretion  propellh  _  I  ae  that  were  formed  before. 
In  the  larger  ducts,  its  propulsion  is  assisted  by  the  contraction 
of  their  walls.  All  the  larger  ducts,  such  as  the  ureter  and 
common  bile-duct,  1  -  —  in  their  coats  plain  muscular  til 
they  contract  when  irritated,  and  sometimes  manifest  peristaltic 
ments.  Rhythmic  contractions  in  the  pancreatic  and  bile- 
ducts  have  been  observed,  and  also  in  the  ureters  and 
deferentia.  It  is  probable  that  the  contractile  power  extends 
along  the  ducts  to  a  considerable  distance  within  the  substance  of 
the  glands  whose  secretions  can  be  rapidly  expelled.  Saliva  and 
milk,  for  instance,  are  sometimes  ejected  with  much  force  ; 
doubtless  by  the  energetic  and  simultaneous  contraction  of  many 
of  the  ducts  of  their  respective  glands. 

Circumstances  Influencing  Secretion. — Amongst  the  prin- 
cipal conditions  which  influence  secretion  are  (1)  variations  in  the 
quantity  of  blood.  (2)  in  the  quantity  of  the  peculiar  materials  for 
any  secretion  that  it  may  contain,  and  (5)  in  conditions  of  the 
nerves  of  the  glands. 

the  quantity  of  blood  t  <  I.  as  in 

nearly  all  the  instances  before  quoted,  coincides  generally  with 
an  augmentation  of  its  secretion.  Thus,  the  mucous  membrane 
of  the  stomach  becomes  florid  when,  on  the  introduction  of  food, 
its  glands  begin  to  secrete  :  the  mammary  gland  becomes  much 
more  vascular  during  lactation  :  and  all  circumstances  which 
rise  to  an  increase   in  the   quantity  of  material   secreted   by  an 

_  .1  produce,  coincidently,  an  increased  supply  of  blood  :  but 
we  have  Been  that  a  discharge  of  saliva  may  occur  under  extra- 
ordinary circumstances,  without  increase  of  blood-supply  (p.  287), 
and  so  it  may  be  inferred  that  this  condition  of  increased  blood- 
supply  is  not  absolutely  essential. 

j  .  1  When  the  blood  contains  more  than  usual  of  the  materials 
which  the   glands  are  designed  to  separate  or  elaborate.     Thus, 

d  :    _ 


404  SECRETION.  [chap,  xi 

when  an  excess  of  nitrogenous  waste  is  in  the  blood,  whether  from 

excessive  exercise,   or  from  destruction  of  one  kidney,  a  healthy 

kidney  will  excrete  more  urea  than  it  did  before. 

(3.)  Influence  of  the  Nervous  System  on  Secretion. — The  process 
» 

of  secretion  is  largely  influenced  by  the  condition  of  the  nervous 
system.  The  exact  mode  in  which  the  influence  is  exhibited  must 
still  be  regarded  as  somewhat  obscure.  In  part,  it  exerts  »its 
influence  by  increasing  or  diminishing  the  quantity  of  blood  supplied 
to  the  secreting  gland,  in  virtue  of  the  power  which  it  exercises 
over  the  contractility  of  the  smaller  blood  vessels  ;  while  it  also 
has  a  more  direct  influence,  as  was  demonstrated  at  length  in  the 
case  of  the  submaxillary  gland,  upon  the  secreting  cells  them- 
selves ;  this  may  be  called  trophic  influence.  Its  influence  over 
secretion,  as  well  as  over  other  functions  of  the  body,  may  be 
excited  by  causes  acting  directly  upon  the  nervous  centres,  upon 
the  nerves  going  to  the  secreting  organ,  or  upon  the  nerves  of 
other  parts.  In  the  latter  case,  a  reflex  action  is  produced  :  thus 
the  impression  produced  upon  the  nervous  centres  by  the  contact 
of  food  in  the  mouth,  is  reflected  upon  the  nerves  supplying  the 
salivary  glands,  and  produces,  through  these,  a  more  abundant 
secretion  of  saliva  (p.  286). 

Through  the  nerves,  various  conditions  of  the  brain  also  influ- 
ence the  secretions.  Thus,  the  thought  of  food  may  be  sufficient 
to  excite  an  abundant  flow  of  saliva.  And,  probably,  it  is  the 
mental  state  which  excites  the  abundant  secretion  of  urine  in 
hysterical  paroxysms,  as  well  as  the  perspirations  and,  occasion- 
ally, diarrhoea,  which  ensue  under  the  influence  of  terror,  and  the 
tears  excited  by  sorrow  or  excess  of  joy.  The  quality  of  a  secretion 
may  also  be  affected  by  the  mind ;  as  in  the  cases  in  which, 
through  grief  or  passion  the  secretion  of  milk  is  altered,  and  is 
sometimes  so  changed  as  to  produce  irritation  in  the  alimentary 
canal  of  the  child,  or  even  death  (Carpenter). 

Relations  between  the  Secretions. — The  secretions  of  some 
of  the  glands  seem  to  bear  a  certain  relation  or  antagonism  to 
each  other,  by  which  an  increased  activity  of  one  is  usually 
followed  by  diminished  activity  of  one  or  more  of  the  others  ; 
and  a  deranged  condition  of  one  is  apt  to  entail  a  disordered 
state  in  the  others.  Such  relations  appear  to  exist  among  the 
various  mucous  membranes ;  and  the  close  relation  between  the 


PHAP.XI.]  STRUCTURE    OF     MAMMARY    (JLANDS. 


405 


secretion  of  the  kidney  ami  that  of  the  skin  is  a  subject  of  constant 
observation. 


The  Mammary  Glands  and  their  Secretion;   Milk. 

Structure.— The  mammary  glands  are  composed  of  large  divi- 
sions or  lobes,  and  these  are  again  divisible  into  lobules, — the 
lobnlcs  being  composed  of  the  convoluted  subdivision  of  ducts 
(alveoli).  The  lobes  and  lobules  are  bound  together  by  areolar 
tissue ;  penetrating  between  the  lobes,  and  covering  the  general 


Fi°\  221. — Dissection  of  the  lower  half  of  the  female  mamma  during  the  period  of  lactation. 
e'g._in  the  left-hand  side  of  the  dissected  part  the  glandular  lobes  are  exposed  and 
partially  unravelled ;  and  on  the  right-hand  side,  the  glandular  substance  has  been 
removed  to  show  the  reticular  loculi  of  the  connective-tissue  in  which  the  glandular 
lobules  are  placed  :  1,  upper  part  of  the  mamilla  or  nipple  ;  2,  areola  ;  3,  subcutaneous 
masses  of  fat ;  4,  reticular  loculi  of  the  connective-tissue  which  support  the  glandular 
substance  and  contain  the  fatty  masses ;  5,  one  of  three  lactiferous  ducts  shown  pass- 
ing towards  the  mamilla  where  they  open  ;  6,  one  of  the  sinus  lactei  or  reservoirs  ;  7, 
some  of  the  glandular  lobules  which  have  been  unravelled  ;  7',  others  massed  to- 
gether (Luschka). 

surface  of  the  gland,  with  the  exception  of  the  nipple,  is  a  considerable 
quantity  of  yellow  fat,  itself  lobulated  by  sheaths  and  processes  of 
tough  areolar  tissue  (fig.  221)  connected  both  with  the  skin  in  front 
and  the  gland  behind  :  'the  same  bond  of  connection  extending  also 
from  the  under  surface  of  the  gland  to  the  sheathing  connective 


4o6  SECRETION.  [chap.  xi. 

tissue  of  the  great  pectoral  muscle  on  which  it  lies.  The  main 
ducts  of  the  gland,  fifteen  to  twenty  in  number,  called  the 
lactiferous  or  galactopho?-ous  ducts,  are  formed  by  the  union  of  the 
smaller  (lobular)  ducts,  and  open  by  small  separate  orifices  through 
the  nipple.  At  the  points  of  junction  of  lobular  ducts  to  form 
lactiferous  ducts,  and  just  before  these  enter  the  base  of  the 
nipple,  the  ducts  are  dilated  (6,  fig.  221);  and,  during  lactation, 
the  period  of  active  secretion  by  the  gland,  the  dilatations  form 
reservoirs  for  the  milk,  which  collects  in  them  and  distends  them. 
The  walls  of  the  gland-ducts  are  formed  of  areolar  and  elastic  with 
some  muscular  tissue,  and  are  lined  internally  by  short  columnar 
and  near  the  nipple  by  squamous  epithelium.  The  alveoli  consist 
of  a  membrana  propria  of  flattened  endothelial  cells  lined  by  low 
columnar  epithelium,  and  are  filled  with  fat.  globules. 

The  nipple,  which  contains  the  terminations  of  the  lactiferous 
ducts,  is  composed  also  of  areolar  tissue,  and  contains  unstriped 
muscular  fibres.  Blood-vessels  are  also  freely  supplied  to  it,  so  as 
to  give  it  a  species  of  erectile  structure.  On  its  surface  are  very 
sensitive  papillre  ;  and  around  it  is  a  small  area  or  areola  of  pink  or 
dark-tinted  skin,  on  which  are  to  be  seen  small  projections  formed 
by  minute  secreting  glands. 

Blood-vessels,  nerves,  and  lymphatics  are  plentifully  supplied  to 
the  mammary  glands  ;  the  calibre  of  the  blood-vessels,  as  well  as 
the  size  of  the  glands,  varying  very  greatly  under  certain  con- 
ditions, especially  those  of  pregnancy  and  lactation. 

Changes  in  the  Glands  at  certain  Periods. — The  minute 
changes  which  occur  in  the  mammary  gland  during  its  periods  of 
evolution  (pregnancy),  and  involution  (when  lactation  has  ceased), 
are  the  following  : — 

The  most  favourable  period  for  observing  the  epithelium  of  the 
mammary  gland  fully  developed  is  shortly  before  the  end  of 
pregnancy.  At  this  period  the  acini  which  form  the  lobules  of 
the  gland,  are  found  to  be  lined  with  a  mosaic  of  polyhedral 
epithelial  cells  (fig.  222),  and  supported  by  a  connective  tissue 
stroma. 

The  rapid  formation  of  milk  during  lactation  results  from  a 
fatty  metamorphosis  of  the  epithelial  cells  :  "  The  secretion  may 
be  said  to  be  produced  by  a  transformation  of  the  substance  of 
successive  generations  of  epithelial  cells,  and  in  the  state  of  full 


chap,  xi.]    CHANGES  IN  THE  GLANDS  DURING   LACTATION    407 

activity  this  transformation  is  so  complete  that  it  may  be  called 
a  deliquescence"  (Creighton). 

hi  the  earlier  days  of  lactation,  epithelial  cells  partially  trans- 
formed  are  discharged  in  the  secretion:  these  arc  termed  "  colos- 


Fig.  222. — Section  of  mammary  gland  of  rabbit  near  the  end  of  pregnancy,  showing  six  acini. 
1",  epithelial  cells  of  a  polyhedral  or  short  columnar  form,  with  which  the  acini  are 
packed.      X  200.     (Schofield.) 

tram  corpuscles,"  but  later  on  the  cells  are  completely  transformed 
before  the  secretion  is  discharged. 

After  the  end  of  lactation,  the  mamma  gradually  returns  to  its 
original  size  {involutioii).  The  acini,  in  the  early  stages  of  involution, 
are  lined  with  eells  in  all  degrees  of  vacuolation  (tig.  223).  As  in- 
volution proceeds  the  acini  diminish  considerably  in  size,  and  at 
length,  instead  of  a  mosaic  of  lining  epithelial  cells  (twenty  to 
thirty  in  each  acinus),  we  have  five  or  six  nuclei  (some  with  no 
surrounding  protoplasm)  lying  in  an  irregular  heap  within  the 
acinus.  During  the  later  stages  of  involution,  large  yellow 
granular  cells  are  to  be  seen.  As  the  acini  diminish  in  size,  the 
connective  tissue  and  fatty  matter  between  them  increase,  and  in 
some  animals,  when  the  gland  is  completely  inactive,  it  is  found 
to  consist  of  a  thin  film  of  glandular  tissue  overlying  a  thick 
cushion  of  fat.  Many  of  the  products  of  waste  are  carried  off  by 
the  lymphatics. 

During  pregnancy  the  mammary  glands  undergo  changes  {evolu- 
tion) which  are  readily  observable.  They  enlarge,  become  harder 
and  more  distinctly  lobulated :  the  veins  011  the  surface  become 
more  prominent.     The  areola  becomes  enlarged  and  dusky,  with 


408 


SECRETION. 


[chap.  XI. 


projecting  papillae  ;  the  nipple  too  becomes  more  prominent,  and 
milk  can  be  squeezed  from  the  orifices  of  the  ducts.  This  is  a  very 
gradual  process,  which  commences  about  the  time  of  conception, 


Tig,  223. — Section  of  mammary  gland,  of  ewe  shortly  after  the  end  of  lactation,  showing  parts 
of  four  acini,  which  contain  numerous  epithelial  cells  undergoing  vacuolation  in  situ  ; 
they  very  closely  resemble  young  fat-cells,  and  are  in  fact  just  like  "  Colostrum  cor- 
puscles." x  300.    (Creighton.) 

and  progresses  steadily  during  the  whole  period  of  gestation.  The 
acini  enlarge,  and  a  series  of  changes  occur,  exactly  the  reverse  of 
those  just  described  under  the  head  of  Involution. 


The  Mammary  Secretion:  Milk. 

Under  the  microscope,  milk  is  found  to  contain  a  number  of 
globules  of  various  sizes  (fig.  224),  the  majority  about  -rohro  of  an 
inch  in  diameter.  They  are  composed  of  oily  matter,  probably 
coated  by  a  fine  layer  of  albuminous  material,  and  are  called  milk- 
globules  ;  while,  accompanying  these,  are  numerous  minute 
particles,  both  oily  and  albuminous,  which  exhibit  ordinary  mole- 
cular movements.  The  milk  which  is  secreted  in  the  first  few 
days  after  parturition,  and  which  is  called  the  colostrum,  differs 
from  ordinary  milk  in  containing  a  larger  quantity  of  solid  matter  ; 
and  under  the  microscope  are  to  be  seen  certain  granular  masses 
called  colostrum-eorfmscles.  These,  which  appear  to  be  small  masses 
of  albuminous  and  oily  matter,  are  probably  secreting  cells  of  the 
gland,  either  in  a  state  of  fatty  degeneration,  or  old  cells  which 
in  their  attempt  at  secretion  under  the  new  circumstances  of 
active  need  of  milk,  are  filled  with  oily  matter ;  which,  however, 


OB  vi'.  xi.]  MILK.  409 

g  unable  to  discharge,  they  are  thei  Bhed    bodily  to 

make  room  for  their  successors.     CJolostrum-corpuscli 


^      °'° 


O      cO 


&0      °«-  °S.<*8>, 


» 


6 f   ~  °    <&&&    o 


oSfe  q8$8g 


% 


k: 


a 


<&&  °y 


Q 

00 


°"cV 


Pig.  224. — Globules  and  m  400. 

seen  to  exhibit  contractile  movements  and  to  squeeze  out  drops  of 
oil  from  their  interior  (Strickei 

Chemical  Composition — Milk  is  in  reality  an  emulsion  con- 
sisting of  numberless  little  globules  of  fat,  coated  with  a  thin  layer 
of  albuminous  matter,  floating  in  a  large  quantity  of  water  which 
contains  in  solution  casein,  serum-albumin,  milk-sugar  (lactose), 
and  several  salts.  Its  percentage  composition  has  been  already 
mentioned,  but  may  be  here  repeated.  Its  reaction  is  alkaline  : 
its  specific  gravity  about  1030. 

Table  of  the  Chemical  Composition  of  Milk. 

Cows. 

•  •  •     858 

.     .      142 


Human 

Water         . 

890 

Solids 

I IO 

IOOO 

Proteids.  including  Casein 

and  Serum-Albumin 

35 

Fats  or  Butter       .         .     . 

25 

Sugar  (with  extractiv 

4s 

Salts           . 

2 

IOOO 

68 

3* 


no  142 


When  milk  is  allowed  to  stand,  the  fat  globules,  being  the 
lightest  portion,  rise  to  the  top,  forming  cream.  If  a  little  acetic 
acid  be  added  to  a  drop  of  milk  under  the  microscope,  the  albu- 


410  THE    SKIN.  [..-hap.  xr. 

minous  film  coating  the  oil  drops  is  dissolved,  and  they  run 
together  into  larger  drops.  The  same  result  is  produced  by  the 
process  of  churning,  the  effect  of  which  is  to  break  up  the 
albuminous  coating  of  the  oil  drops  :  they  then  coalesce  to  form 
butter. 

Curdling  of  Milk. — If  milk  be  allowed  to  stand  for  sonic 
time,  its  reaction  becomes  acid  :  in  popular  language  it  "  turns 
sour."  This  change  appears  to  be  due  to  the  conversion  of  the 
milk-sugar  into  lactic  acid,  which  causes  the  precipitation  of  the 
casein  (curdling)  :  the  curd  contains  the  fat  globules  :  the  remain- 
ing fluid  (whey)  consists  of  water  holding  in  solution  albumin, 
milk-sugar  and  certain  salts.  The  same  effect  is  produced  in  the 
manufacture  of  cheese,  which  is  really  casein  coagulated  by  the 
agency  of  rennet  (p.  307).  "When  milk  is  boiled,  a  scum  of  serum- 
albumin  forms  on  the  surface. 

Curdling  Ferments. — The  effect  of  the  ferments  of  the 
gastric,  pancreatic,  and  intestinal  juices  in  curdling  milk 
{curdling  ferments)  has  already  been  mentioned  in  the  Chapter 
on  Digestion. 

The  salts  of  milk  are  chlorides,  sulphates,  phosphates,  and 
carbonates  of  potassium,  sodium,  calcium. 


CHAPTEE    XII. 

THE    SKIX    AND    ITS    FUNCTIONS. 

The  skin  serves — (1),  as  an  external  integument  for  the  pro- 
tection of  the  deeper  tissues,  and  (2),  as  a  sensitive  organ  in  the 
exercise  of  touch ;  it  is  also  (3),  an  important  excretoiy,  and  (4), 
an  absorbing  organ  ;  while  it  plays  an  important  part  in  (5)  the 
regulation  of  the  temperature  of  the  body. 

Structure  of  the  Skin. — The  skin  consists,  principally,  of  a 
vascular  tissue,  named  the  corium,  derma,  or  cutis  vera,  and  an 
external  covering  of  epithelium  termed  the  cuticle  or  epidermis. 
"Within  and  beneath  the  corium  are  imbedded  several  organs  with 


»  BA2.   XII.] 


STRUCTUKK    OF    'III K    EPLDEfiMIS. 


4II 


Bpeda]  function,  namely  red  _  glandfl,  and 

hair  follicles ;   and  on    its   Surface    BJ  The  so- 

called  aji pendagee  of  the  akin — the  hair  and  nails — are  modifica- 

US  of  the  enideri: 

Epidermis. — The  epidermis  is  composed  of  several  strata  of 
cells  of  various  sliaj.es,  and  closely  resembles  in  its  structure  that 
which  lines  the  mouth.  The  following  four  layers  may  be  dis- 
tinguished. 1.  Stratum  eomeum  (fig.  225.  a),  consisting  of  many 
superposed  layers  of 
horny  Bcales.  The 
different  thickness  of 
the  epidermis  in  dif- 
ferent regions  of  the 
body  is  chiefly  due 
to  variations  in  the 
thickness  of  this 
layer ;  e.g.,  on  the 
horny  parts  of  the 
palms  of  the  hands 
and  soles  of  the  feet 
it  is  of  great  thick- 
ness. The  stratum 
eomeum  of  the  buc- 
cal epithelium  chiefly 
differs  from  that  of 
the  epidermis  in  the 
fact  that  nuclei  are 
to  be  distinguished 
in  some  of  the  cells 
even  of  its  most 
superficial  layers. 

2.  Stratum  lucidum, 
a   bright   homogene- 
ous membrane  consisting  of  squamous  cells  closely  arranged,  in 
some  of  which  a  nucleus  can  be  seen. 

3.  Stratum  granulosum,  consisting  of  one  layer  of  flattened  cells 
which  appear  fusiform  in  vertical  section  :  they  are  distinctly 
nucleated,  and  a  number  of  granules  extend  from  the  nucleus  to 
the  margins  of  the  cell. 


:. 


N> 


d 

..1 


^ 


Fig.  225. —  Vertical  section  of  Hu 

.  -tratum  eomeum,  of  very  few  layers,  the  stratum 
lueidum  and  stratum  granuiosum  not  being  distinctly 
represented  :  b,  c.  d,  and  ■%  the  layers  of  the  stratum 
Malpighi,  a  certain  number  of  the  cells  in  layers  <l  and 
e  showing  signs  of  segmentation ;  layer  r  consists  chiefly 
of  prickle  or  ridge  and  furrow  cells  :  /.  basement  mem- 
brane ;  f,  cells  in  cutis  vera.      Cadiat. 


412 


THE    SKIN. 


[chap.  XII. 


4.  Stratum  Malpighii  or  Itete  mucosum,  which  consists  of  many 
strata.  The  deepest  cells,  placed  immediately  above  the  cutis 
vera,  are  columnar  with  oval  nuclei :  this  layer  of  columnar  cells 
is  succeeded  by  a  number  of  layers  of  more  or  less  polyhedral 
cells  with  spherical  nuclei ;  the  cells  of  the  more  superficial  layers 
are  considerably  flattened.  The  deeper  surface  of  the  rete 
mucosum  is  accurately  adapted  to  the  papillae  of  the  true  skin, 
being,  as  it  were,  moulded  on  them.  It  is  very  constant  in  thick- 
ness in  all  parts  of  the  skin. 
The  cells  of  the  middle  layers  of 
the  stratum  Malpighii  are  almost 
all  connected  by  processes,  and 
thus  form  "prickle  cells"  (p.  24). 
The  pigment  of  the  skin,  the 
varying  quantity  of  which  causes 
the  various  tints  observed  in  dif- 
ferent individuals  and  different 
races,  is  contained  in  the  deeper 
cells  of  the  rete  mucosum ;  the 
pigmented  cells  as  they  approach 
the  free  surface  gradually  losing 
their  colour.  Epidermis  main- 
tains its  thickness  in  spite  of  the 
constant  wear  and  tear  to  which 
it  is  subjected.  The  columnar 
cells  of  the  deepest  layer  of  the 
"  rete  mucosum  "  elongate,  and 
their  nuclei  divide  into  two  (fig. 
225,  e).  Lastly  the  upper  part  of 
the  cell  divides  from  the  lower  ; 
thus  from  a  long  columnar  cell  are  produced  a  polyhedral  and  a 
short  columnar  cell :  the  latter  elongates  and  the  process  is  repeated. 
The  polyhedral  cells  thus  formed  are  pushed  up  towards  the  free 
surface  by  the  production  of  fresh  ones  beneath  them,  and  become 
flattened  from  pressure :  they  also  become  gradually  horny  by 
evaporation  and  transformation  of  their  protoplasm  into  keratin, 
till  at  last  by  rubbing  they  are  detached  as  dry  homy  scales  at 
the  free  surface.  There  is  thus  a  constant  production  of  fresh 
cells  in  the  deeper  layers,  and  a  constant  throwing  off  of  old  ones 


Fig.  226. —  Vertical  section  of  skin  of  the 
negro,  a,  a.  Cutaneous  papillae,  b. 
Undermost  and  dark-coloured  layer 
of  oblong  vertical  epidermis -cells. 
c.  Stratum  Malpighii.  d.  Superfi- 
cial layei's,  including  stratum  cor- 
neum,  stratum  lucidum,  and  stratum 
granulosum,  the  last  two  not  differen- 
tiated in  fig.  x  250  (Sharper.) 


CHAT.    XII.] 


(  vi  is  vkua  :    r.\rii.i..i:. 


4i3 


from  the  free  surface.     When  these  two  pn  iccurately 

balanced,  the  epidermis  maintains  its  thickness.     When,  by  infc 
mittent  pressure   a   more   active  cell-growth  is   stimulated,    the 

production  of  cells  exceeds  their  waste  and  the  epidermis  in< 
in  thickness,  as  we  see  in  the  horny  hands  of  the  labourer. 

The  thickness  of  the  epidermis  on  different  portions  of  the  skin 
is  directly  proportioned  to  the  friction,  pressure,  and  other  sour 

of  injury  to  which  it  is  exposed  ;  for  it  serve-  as  well  to  protect  the 
sensitive  and  vascular  cutis  from  injury  from  without,  as  to  limit 
the  evaporation  of  fluid  from  the  blood-vessels.  The  adaptation  of 
the  epidermis  to  the  latter  purposes  may  be  well  shown  by 
exposing  to  the  air  two  dead  hands  or  feet,  of  wdiich  one  has 
its  epidermis  perfect,  and  the  other  is  deprived  of  it ;  in  a 
•  lay,  the  skin  of  the  latter  will  become  brown,  dry,  and  horn- 
like, while  that  of  the  former  will  almost  retain  its  natural 
moisture. 

Cutis  vera. — The  corium  or  cutis,  which  re^ts  upon  a  layer  of 
adipose  and  cellular  tissue  of  varying  thickness,  is  a  dense  and 
tough,  but  yielding  and  highly  elastic  structure,  composed  of 
fasciculi  of  fibro-eellular  tissue,  interwoven  in  all  directions,  and 
forming,  by  their  interlacements,  numerous  spaces  or  areolae. 
These  areolae  are  large  in  the  deeper  layers  of  the  cutis,  and  are 
there  usually  tilled  with  little  masses  of  fat  (rig.  22S)  :  but,  in  the 
superficial  parts,  they  are  small  or  entirely  obliterated.  Plain 
muscular  fibre  is  also  abundantly  present. 

Papillae. — The  papillae  are  conical  elevations  of  the  cutis  vera, 
with  a  single  or  divided  free  extremity,  more  prominent  and  more 


Fig.  227. — Compound  \  basis  of  a  papilla  :  t ,  b,  divi- 

sions or  branches  of  the  same  :  <-.  e,  branches  belonging  to  papilhe.  of  which  the  bases 
are  hidden  from  view,    x  60  vKolilkvr  . 

densely  set  at  some  parts  than  at  others  (figs.  227  and  230).     The 
parts  on  which  they  are  most  abundant  and  most  prominent,  are 


414 


THE    SKIN. 


[CHAP.  XII. 


the  palmar  surface  of  the  hands  and  fingers,  and  the  soles  of  the 
feet — parts,  therefore,  in  which  the  sense  of  touch  is  most  acute. 
On   these   parts   they  are  disposed   in  double   rows,  in   parallel 


curved  lines,  separated  from 
each  other  by  depressions. 
Thus  they  may  be  seen  easily 
on  the  palm,  whereon  each 
raised  line  is  composed  of  a  double  row 
of  papillae,  and  is  intersected  by  short 
transverse  lines  or  furrows  correspond- 
ing with  the  interspaces  between  the 
successive  pairs  of  papillse.  Over  other 
parts  of  the  skin  they  are  more  or  less 
thinly  scattered,  and  are  scarcely  ele- 
vated above  the  surface.  Their  average 
length  is  about  -^  of  an  inch,  and  at 
their  base  they  measure  about  T-\^  of  an 
inch  in  diameter.  Each  papilla  is  abundantly  supplied  with  blood, 
receiving  from  the  vascular  plexus  in  the  cutis  one  or  more 
minute  arterial  twigs,  which  divide   into    capillary  loops    in  its 


pjo-  228.— Vertical  section  of  skin. 
CA  Sebaceous  gland  opening 
into  hair-follicle.  B.  Muscu- 
lar fibres.  C.  Sudoriferous 
or  sweat-gland.  D.  Subcu- 
taneous fat.  E.  Fundus  of 
hair-follicle,  with  hair-papilhe . 
(Klein  and  Noble  Smith.) 


CHAR  XII. J 


NERVE-TERMINATIONS. 


415 


substance,  and  then  reunite  into  a  minute  vein,  which  pnnnm  out 
at  its  base.  The  abundant  supply  of  blood  which  the  papillae 
thus  receive  explains  the  turgescence  or  kind  of  erection  which 
undergo  when  the  <•iivulatii.ii  through  the  skin  La  active. 
The  majority,  but  not  nil,  of  the  papillae  contain  also  one  or  more 
terminal  nerve-fibres,  from  the  ultimate  ramifications  of  the 
cutaneous  plexus,  on  which  their  exquisite  sensibility  depends. 

Nerve-terminations. — In  some  parts,  especially  those  in 
which  the  sense  of  touch  is  highly  developed,  as,  for  example, 
the  palm  of  the  hand  and  the  lips,  the  nerve-fibres  appear  to 
terminate,  in  many  of  the  papillae,  by  one  or  more  free  ends  in 
the  substance  of  an  oval-shaped  body,  occupying  the  principal 
part  of  the  interior  of  the  papilla,  and  termed  a    touch-corpuscle 


Fig".  229. — Papilke  from  ih-  skin  of  the  hand,  freed  from  the  cuticle  and  exhibiting  tactile 
corpusi-k-.  a.  Simpie  papilla  with  four  nerve-fibres  :  a,  tactile  corpuscles  ;  b,  nen 
b.  Papilla  treated  with  acetic  acid  ;  a,  cortical  layer  with  cells  and  fine  elastic  fila- 
ments ;  b,  tactile  corpuscle  with  transverse  nuclei ;  c,  entering-  nerve  with  neurilemma 
or  perineurium  ;  d,  nerve-fibres  winding  round  the  corpuscle,  c.  Papilla  viewed  from 
above  so  as  to  appear  as  a  cross  section  :  <•/,  cortical  layer  :  b,  nerve-fibre  ;  c,  sheath  01 
the  tactile  corpuscle  containing  nuclei ;  d,  core.     X  350.  (Kollikei . 


(fig.  229).  The  nature  of  this  body  is  obscure.  Some  regard  it 
as  little  else  than  a  mass  of  fibrous  or  connective  tissue,  sur- 
rounded by  elastic  fibres,  and  formed,  according  to  Huxley,  by 
an  increased  development  of  the  primitive  sheaths  of  the  n< 
fibres,  entering  the  papilla?.  Others,  however,  believe  that, 
instead  of  thus  consisting  of  a  homogeneous  mass  of  connective 
tissue,  they  are  special  and  peculiar  bodies  of  laminated  structure, 
directly  concerned  in  the  sense  of  touch.     They  do  not  occur  in 


4i6 


THE    SKIN. 


[CHAP.  XII. 


all  the  papillae  of  the  parts  where  they  are  found,  and,  as  a  rule, 
in  the  papillae  in  which  they  are  present  there  are  no  blood- 
vessels. Since  these  peculiar  bodies  in  which  the  nerve-fibres  end 
are  only  met  with  in  the  papillae  of  highly  sensitive  parts,  it  may 
be  inferred  that  they  are  specially  concerned  in  the  sense  of  touch, 
yet  their  absence  from  the  papillae  of  other  tactile  parts  shows  that 
they  are  not  essential  to  this  sense. 

Closely  allied  in  structure  to  the  touch-corpuscles  are  some  little 
bodies  called  end-bulbs,  about  ^^  inch  in  diameter  (Krause).     They 


Kg.  230. — End-bulbs  in  papillae  (magnified)   treated  with  acetic  acid,     a,  from  the  lips  ; 
C  the  white  loops  in  one  of  them  are  capillaries,    b,  from  the  tongue.    Two  end-bulbs 
seen  in  the  midst  of  the  simple  papilhe :  a,  a,  nerves  (Kolliker) . 

are  generally  oval  or  spheroidal,  and  composed  externally  of  a 
coat  of  connective  tissue  enclosing  a  softer  matter,  in  which  the 
extremity  of  a  nerve  terminates.  These  bodies  have  been  found 
chiefly  in  the  lips,  tongue,  palate,  and  the  skin  of  the  glans  penis 
(fig.  230). 

Glands  of  the  Skin. — The  skin  possesses  glands  of  two  kinds ; 
(a)  Sudoriferous,  or  Sweat  Glands ;  (6)  Sebaceous  Glands. 

(a)  Sudoriferous,  or  Sweat  Glands. — Each  of  these  glands  con- 
sists of  a  small  lobular  mass,  formed  of  a  coil  of  tubular  gland- 
duct,  surrounded  by  blood-vessels  and  embedded  in  the  sub- 
cutaneous adipose  tissue  (fig.  228,  a).  From  this  mass,  the  duct 
ascends,  for  a  short  distance    in    a  spiral  manner  through   the 


i  hap,  xii.]  GLANDS, 


417 


deeper  part  of  the  cutis,  then  passing  Btraight,  and  then  sometimes 
again  becoming  spiral,  it  passes  through  the  cuticle  and  opens  by 
an  oblique  valve-like  aperture.  In  the  parts  where  the  epidermis 
is  thin,  the  ducts  themselves  are  thinner  and  more  nearly  Btraight 

in  their  course  (fig.  22S).  The  duct,  which  maintains  nearly  the 
same  diameter  throughout,  is  lined  with  a  layer  of  columnar 
epithelium  (fig.  231)  continuous  with  the  epidermis;  while  the 
part  which  passes  through  the  epidermis  is  composed  of  the  latter 


Fig.  231.—  '.  of  sudoriferous  gland,  divided  in  various  direction?,     n,  sheath  of  the 

gland ;  b,  columnar  epithelial  lining  of  gland  tube ;    c,   lumen  of    tube ;  </,  divided 
blood-vessel ;  /,  loose  connective-tissue,  forming  a  capsule  to  the  gland  (Biesiadecki  . 

structure  only ;  the  cells  which  immediately  form  the  boundary 
of  the  canal  in  this  part  being  somewhat  differently  arranged  from 
those  of  the  adjacent  cuticle. 

The  sudoriferous  glands  are  abundantly  distributed  over  the 
whole  surface  of  the  body ;  but  are  especially  numerous,  as  well 
as  very  large,  in  the  skin  of  the  palm  of  the  hand,  and  of  the  sole 
of  the  foot.  The  glands  by  which  the  peculiar  odorous  matter  of 
the  axillae  is  secreted  form  a  nearly  complete  layer  under  the 
cutis,  and  are  like  the  ordinary  sudoriferous  glands,  except  in 
being  larger  and  having  very  short  ducts. 

The  peculiar  bitter  yellow  substance  secreted  by  the  skin  of 
the  external  auditory  passage  is  named  cervmen,  and  the  glands 
themselves  ceruminous  glands;  but  they  do  not  much  differ  in 
structure  from  the  ordinary  sudoriferous  glands. 

(b)  Sebaceous  Glands. — The  sebaceous  glands  (fig.  232),  like 
the  sudoriferous  glands,  are  abundantly  distributed  over  most 
parts  of  the  body.      They  are  most   numerous  in  parts  largely 

E  E 


41 8  THE    SKIX.  [chap.  xm. 

supplied  with  hair,  as  the  scalp  and  face,  and  are  thickly  distributed 
about  the  entrances  of  the  various  passages  into  the  body,  as  the 
anus,  nose,  lips,  and  external  ear.  They  are  entirely  absent  from 
the  palmar  surface  of  the  hand   and  the  plantar  surfaces  of  the 


Fig.  232. — Sebaceous  gland  from  human  skin  (Klein  and  Noble  Smith". 

feet.  They  are  minutely  tabulated  glands  composed  of  an  aggre- 
gate of  small  tubes  or  sacculi  filled  with  opaque  white  substance?, 
like  soft  ointment.  Minute  capillary  vessels  overspread  them  : 
and  their  ducts  open  either  on  the  surface  of  the  skin,  close  to  a 
hair,  or,  which  is  more  usual,  directly  into  the  follicle  of  the  hair. 
In  the  latter  case,  there  are  generally  two  or  more  glands  to  each 
hair  (fig.  228). 

Hair. — A  hair  is  produced  by  a  peculiar  growth  and  modifica- 
tion of  the  epidermis.  Externally  it  is  covered  by  a  layer  of 
fine  scales  closely  imbricated,  or  overlapping  like  the  tiles  of  a 
house,  but  with  the  free  edges  turned  upwards  (fig.  233,  a).  It 
is  called  the  cuticle  of  the  hair.  Beneath  this  is  a  much  thicker 
layer  of  elongated  horny  cells,  closely  packed  together  so  as   to 


«  HAP.    XII. J 


BAIR. 


419 


resemble  a  fibrous  stmcture.     This,  very  commonly,  in  the  human 
subject,  occupied  the  whole  of  the  inside  of  the  hair  ;  but  in  - 


J. 


- 


Kg.  233.— Surface  of  0  white  hmr,  magnified  160  diameters.  The  wave  lines  mark  th- 
upper  or  free  edges  of  the  cortical  scales.  B,  separated  scales,  magnified  350  dia- 
meters (Kiilliker  . 

cases  there  is  left  a  small  central  space  filled  by  a  substance  called 


Kg.  234. — Medium-sized  hair  m  it*  follicle,  a,  stem  tut  short ;  h,  root ;  c,  knob ;  d,  hair 
cuticle  ;  e,  internal,  and/,  external  root-sheath  ;  ,7,  h,  dermic  coat  of  follicle  ;  i,  papilhi : 
*,  k,  ducts  of  sebaceous  glands;  /,  corium;  m,  mucous  layer  of  epidermis;  0,  upper 
limit  of  internal  root  sheath  x  50  (Kolliker).    See  also  fig.  235. 

E   E   2 


420 


THE    SKIN. 


[CHAP.  XII. 


the  medulla  or  pith,  composed  of  small  collections  of  irregularly 
shaped  cells,  containing  sometimes  pigment  granules  or  fat,  but 
mostly  air. 

The  follicle,   in  which  the  root  of  each  hair  is  contained  (fig. 


e> 


pjc  2,- Magnified  view  of  the  root  of  a  hair,    a,  stem  or  shaft  of  hair  cut  across;  b,  inner, 

°'and  c  outer  layer  of  the  epidermal  lining  of  the  hair-follicle,  called  also  the  inner  and 
outer  'root-sheath  ;  d,  dermal  or  external  coat  of  the  hair-follicle,  shown  in  part,  e, 
imbricated  scales  about  to  form  a  cortical  layer  on  the  surface  of  the  hair.  The  adja- 
cent cuticle  of  the  root-sheath  is  not  represented,  and  the  papilla  is  hidden  in  the 
lower  part  of  the  knob  where  that  is  represented  lighter  (Kohlrausch). 

235),  forms  a  tubular  depression  from  the  surface  of  the  skin, — 
descending  into  the  subcutaneous  fat,  generally  to  a  greater 
depth  than  the  sudoriferous  glands,  and  at  its  deepest  part 
enlarging  in  a  bulbous  form,  and  often  curving  from  its  previous 
rectilinear  course.  It  is  lined  throughout  by  cells  of  epithelium, 
continuous  with  those  of  the  epidermis,  and  its  walls  are  formed 
of  pellucid  membrane,  which  commonly,  in  the  follicles  of  the 
largest  hairs,  has  the  structure  of  vascular  fibrous  tissue.  At 
the  bottom  of  the  follicle  is  a  small  papilla,  or  projection  of  true 
skin  and  it  is  by  the  production  and  out-growth  of  epidermal 
cells  from  the  surface  of  this  papilla  that  the  hair  is  formed.  The 
inner  wall  of  the  follicle  is  lined  by  epidermal  cells  continuous 
with  those  covering  the  general  surface  of  the  skin ;  as  if  indeed 
the  follicle  had  been  formed  by  a  simple  thrusting  in  of  the  surface 
of  the  integument  (fig.  234).     This  epidermal  lining  of  the  hair- 


OHAP.  Mi. J 


NAILS. 


421 


follicle,  1  heath  of  the  hair,  is  composed  of  tw<  .  the 

inner  one  of  which  is  so  moulded  on  the  imbricated  seal y  cuticle 
of  the  hair,  that  its  inner  surface  becomes  imbricated  also,  but  of 
course  in  the  opposite  direction.     When  a  hair  is  pulled  out,  the 
inner    layer    of    the 
rootsheath    and    part 
of   the    outer    layer 
also    are    commonly 
pulled  out  with  it. 

Nails.  —  A     nail, 
like  a  hair,  is  a  pecu-  i 

liar    arrangement   of       1 
epidermal    cells,    the 
undermost  of  which, 
like     those     of     the    J-* 

eral     surface      of 
the   integument,    are     /*1 
rounded  or  elongated,       J\ 
while   the   superficial       -j    V.;V 
are  flattened,  and  of 
more    horny    consist- 
ence.    That  specially  T- 
modified    portion    of 

Fig.  256. — T  f'a  hair  and  Jmir-foUicle  made 

the     COrilim,     01'     true  below  the  opening  of  the  sebaceous  gland,    a,  medulla 

.  .          .              ,  .  ,       ,,  or  pith  of  the  hair  ;  b,  hbrous  la ver  or  cortex ;  c,  cuticle  ; 

Skill,     by     Which     the  d,  Huxley's  layer,  e,  Henle's  layer  of  internal  root- 

.,                           ,     1        .  sheath  ;/ and  .7,  layers  of  external  root-sheath,  outside 

nail      IS      Secreted.,      IS  of  a  is  a  light  layer,  or  "glassy  membrane,"  which  is 

„     -.    .-,              .    •  equivalent  to  the  basement  membrane  ;  h,  fibrous  coat 

Called  the  matrix.  of  hair  sac ;  t,  vessels.     (Cadiat.; 

The  back  edge  of 
the  nail,  or  the  root  as  it  is  termed,  is  received  into  a  shallow 
crescentic  groove  in  the  matrix,  while  the  front  part  is  free 
and  projects  beyond  the  extremity  of  the  digit.  The  inter- 
mediate portion  of  the  nail  rests  by  its  broad  under-surface  on 
the  front  part  of  the  matrix,  which  is  here  called  the  bed  of  the 
nail.  This  part  of  the  matrix  is  not  uniformly  smooth  on  the 
surface,  but  is  raised  in  the  form  of  longitudinal  and  nearly 
parallel  ridges  or  laminae,  on  which  are  moulded  the  epidermal 
cells  of  which  the  nail  is  made  up  (fig.  237). 

The  growth  of  the  nail,  like  that  of  the  hair,  or  of  the  epidermis 
generally,  is  effected  by  a  constant  production  of  cells  from  beneath 


422 


THE    SKIN. 


[chap.  xii. 


and  behind,  to  take  the  place  of  those  which  are  worn  or  cut 
away.  Inasmuch,  however,  as  the  posterior  edge  of  the  nail,  from, 
its  being  lodged  in  a  groove  of  the  skin,  cannot  grow  backwards, 
on  additions  being  made  to  it,  so  easily  as  it  can  pass  in  the 
opposite  direction,  any  growth  at  its  hinder  part  pushes  the  whole 
forwards.  At  the  same  time  fresh  cells  are  added  to  its  under 
surface,  and  thus  each  portion  of  the  nail  becomes  gradually 
thicker  as  it  moves  to  the  front,  until,  projecting  beyond  the 


Fig.  237. — Vertical  transverse  section  through  a  small  portion  of  th?  nail  and  matrix  largely 
magnified.  A,  corium  of  the  nail-bed,  raised  into  ridges  or  lamina-  a,  fitting  in  between 
corresponding  laminae  b,  of  the  nail.  B,  llalpighian,  and  C,  horny  layer  of  nail :  d, 
deepest  and  vertical  cells  ;  e,  upper  flattened  cells  of  Malpighian  layer  (Kolliker). 

surface  of  the  matrix,  it  can  receive  no  fresh  addition  from  beneath, 
and  is  simply  moved  forwards  by  the  growth  at  its  root,  to  be  at 

last  worn  away  or  cut  off. 


Functions  of  the  Skin. 

(1.)  By  means  of  its  toughness,  flexibility  and  elasticity,  the 
skin  is  eminently  qualified  to  serve  as  the  general  integument  of  the 
bod}-,  for  defending  the  internal  parts  from  external  violence,  and 
readily  yielding  and  adapting  itself  to  their  various  movements 
and  changes  of  position. 

(2.)  The  skin  is  the  chief  organ  of  the  sense  of  touch.     Its 


CHAP.  XII.]       SECRETION    OF    SEBACEOUS    GLANDS. 


423 


whole  surface  is  extremely  sensitive;  but  its  tactile  properties  are 
slue  more  especially  to  the  abundant  papillae  with  which  it  is 
studded.     (See  Chapter  on  Special  Senses.) 

Although  destined  especially  for  the  sense  of  touch,  the  papillae 
ire  not  so  placed  as  to  come  into  direct  contact  with  external 
objects  ;  but  like  the  rest  of  the  surface  of  the  skin,  are  covered 
by  one  or  more  layers  of  epithelium,  forming  the  cuticle  or 
epidermis.  The  papillae  adhere  very  intimately  to  the  cuticle, 
which  is  thickest  in  the  spaces  between  them,  but  tolerably 
level  on  its  outer  surface :  hence,  when  stripped  off  from  the  cutis, 

after  maceration,  its  internal  surface  presents  a  series  of  pits 
ami  elevations  corresponding  to  the  papillse  and  their  interspaces, 
of  which  it  thus  forms  a  kind  of  mould.  Besides  affording  by  its 
impermeability  a  check  to  undue  evaporation  from  the  skin,  and 
providing  the  sensitive  cutis  with  a  protecting  investment,  the 
cuticle  is  of  service  in  relation  to  the  sense  of  touch.  For  by 
being  thickest  in  the  spaces,  between  the  papillse,  and  only  thinly 
spread  over  the  summits  of  these  processes,  it  may  serve  to  sub- 
divide the  sentient  surface  of  the  skin  into  a  number  of  isolated 
points,  each  of  which  is  capable  of  receiving  a  distinct  impression 
from  an  external  body.  By  covering  the  papillse  it  renders  the 
sensation  produced  by  external  bodies  more  obtuse,  and  in  this 
manner  also  is  subservient  to  touch  :  for  unless  the  very  sensitive 
papillae  were  thus  defended,  the  contact  of  substances  would  give 
rise  to  pain,  instead  of  the  ordinary  impressions  of  touch.  This 
is  shown  in  the  extreme  sensitiveness  and  loss  of  tactile  power  in 
a  part  of  the  skin  when  deprived  of  its  epidermis.  If  the  cuticle 
is  very  thick,  however,  as  on  the  heel,  touch  becomes  imperfect,  or 
is  lost. 

(3.)  The  Secretion  of  Sebaceous  Glands,  and  Hair 
follicles. — The  secretion  of  the  sebaceous  glands  and  hair- 
follicles  (for  their  products  cannot  be  separated)  consists  of  cast-off 
epithelium-cells,  with  nuclei  and  granules,  together  with  an  oily 
matter,  extractive  matter,  and  stearin  ;  in  certain  parts,  also,  it  is 
mixed  with  a  peculiar  odorous  principle,  which  contains  caproic, 
butyric,  and  rutic  acids.  It  is,  perhaps,  nearly  similar  in  compo- 
sition to  the  unctuous  coating,  or  vernix  caseosa,  which  is  formed 
on  the  body  of  the  foetus  while  in  the  uterus,  and  which  contains 
large  quantities  of  ordinary  fat.     Its  purpose  seems  to  be  that  of 


424  TnE    SKIN.  [CHAP.  XII. 

keeping  the  skin  moist  and  supple  and,  by  its  oily  nature,  of  both 
hindering  the  evaporation  from  the  surface,  and  guarding  the 
skin  from  the  effects  of  the  long-continued  action  of  moisture. 
But  while  it  thus  serves  local  purposes,  its  removal  from  the 
body  entitles  it  to  be  reckoned  among  the  excretions  of  the  skin  ; 
though  the  share  it  has  in  the  purifying  of  the  blood  cannot  be 
discerned. 

(4.)  The  Excretion  of  the  Skin:  the  Sweat. — The  fluid 
secreted  by  the  sudoriferous  glands  is  usually  formed  so  gradually, 
that  the  watery  portion  of  it  escapes  by  evaporation  as  fast  as  it 
reaches  the  surface.  But,  during  strong  exercise,  exposure  to 
great  external  warmth,  in  some  diseases,  and  when  evaporation  is 
prevented,  the  secretion  becomes  more  sensible,  and  collects  on  the 
skin  in  the  form  of  drops  of  fluid. 

The  perspiration  of  the  skin,  as  the  term  is  sometimes  employed, 
in  physiology,  includes  all  that  portion  of  the  secretions  and 
exudations  from  the  skin  which  passes  off  by  evaporation  ;  the 
sweat  includes  that  which  may  be  collected  only  in  drops  of  fluid 
on  the  surface  of  the  skin.  The  two  terms  are,  however,  most 
often  used  synonymously ;  and  for  distinction,  the  former  is  called 
insensible  perspiration;  the  latter  sensible  perspiration.  The  fluids 
are  the  same,  except  that  the  sweat  is  commonly  mingled  with 
various  substances  lying  on  the  surface  of  the  skin.  The  contents 
of  the  sweat  are,  in  part,  matters  capable  of  assuming  the  fomi  of 
vapour,  such  as  carbonic  acid  and  water,  and  in  part,  other- 
matters  which  are  deposited  on  the  skin,  and  mixed  with  the 
sebaceous  secretion. 

Table  of  the  Chemical  Composition  of  Sweat. 

Water 995 

Solids  :— 


Organic  Acids  (formic,  acetic,  butyric,  \ 


9 


propionic,  caproic.  caprvlic) 
Salts,  chiefly  sodium  chloride  ,  .  ,  r§ 
Neutral  fats  and  cholesterin  ...  7 
Extractives  (including  urea),  with  epi- )  - 

thelium  .         .         .         .         .     .  J 


1000 


Of  these  several  substances,  however,  only  the  carbonic  acid  and 
water  need  particular  consideration. 


ojiap.  xii.]  THE    SWEAT.  425 

Watery  vapour. — The   quantity   of  u  excreted 

from   the   -kin    is  on  an  aver  e  ■    ■  j    md  2  lb.  daily. 

Thia  subject  hae  carefully  by  \.  and 

Sequin.     The  latter  ch<  closed  1  in  an  aii-t  _ 

with  a  mouth-piece.  The  bag  being  closed  by  a  Btrong  band 
above,  and  the  mouth-piece  adjusted  and  gummed  to  the  skin 
around  the  month,  he  was  weighed,  and  then  remained  quiet  for 
several  hours,  after  which  time  he  was  again  weighed.  The 
difference  in  the  two  v  indicated   the  amount  of 

pulmonary  exhalation.  Having  taken  off  the  air-tight  dress,  he 
immediately  weighed  again,  and  a  fourth  time  after  a  certain 
interval.  The  difference  between  the  two  weights  last  ascertained 
gave  the  amount  of  the  cutaneous  and  pulmonary  exhalation  to- 
gether: by  subtracting  from  thia  the  loss  by  pulmonary  exhalation 
alone,  while  he  was  in  the  air-tight  dress,  he  ascertained  the 
amount  of  cutaneous  transpiration.  During  a  state  of  rest,  the 
averag  sa  by  cutaneous  and  pulmonary  exhalation  in  a  minute, 
is  eighteen  grains, — the  minimum  eleven  grains,  the  maximum. 
thirty-two  grains  ;  and  of  the  eighteen  grains,  eleven  pass  off  by 
the  skin,  and  seven  by  the  lungs. 

The  quantity  of  watery  vapour  lost  by  transpiration  is  of  course 
influenced  by  all  external  circumstances  which  affect  the  exhala- 
froni  other  evaporating  surfaces,  such  as  the  temperature, 
the  hygrometric  state,  and  the  stillness  of  the  atmosphere.  But, 
of  the  variations  to  which  it  is  subject  under  the  influence  ofthese 
conditions,  no  calculation  has  been  exactly  made. 

Carbonic  Acid. — The  quantity  of  carbonic  acid  exhaled  by  the 
skin  on  an  average  is  about  T^-  to  — ^  of  that  furnished  by  the 
pulmonary  respiration. 

The  cutaneous  exhalation  is  most  abundant  in  the  lower  classes  of  animals,, 
more  particularly  the  naked  Amphibia,  as  frogs  and  toads,  whose  skin  is 
thin  and  moist,  and  readily  permits  an  interchange  of  gases  between  the 
blood  circulating  in  it  and  the  surrounding  atmosphere.  Eischoff  found 
that,  after  the  lungs  of  frogs  had  been  tied  and  cut  out,  about  a  quarter  of  a 
cubic  inch  of  carbonic  acid  gas  was  exhaled  by  the  skin  in  eight  hours. 
And  this  quantity  is  very  lar^e.  when  it  is  remembered  that  a  full-sized  frog 
will  generate  only  about  half  a  cubic  inch  of  carbonic  acid  by  his  lungs  and 
skin  together  in  six  -.     (Milne-Edwards  and  Miiller.) 

The  importance  of  the  respiratory  function  of  the  skin,  which  was  once 
thought  to  be  proved  by  the  speedy  death  of  animals  whose  skins,  after 
removal  of  the  hair,  were  covered  with  an  impermeable  varnish,  has  been 
shown  by  further  observations  to  have  no  foundation  in  fact ;  the  immediate 


426  THE     SKIN-  [CHAP.  XII. 

cause  of  death  in  such  cases  being  the  loss  of  temperature.  A  varnished 
animal  is  said  to  have  suffered  no  harm  when  surrounded  by  cotton  wadding, 
and  to  have  died  when  the  wadding  was  removed. 

Influence  of  the  Nervous  System  on  Excretion. — Any 

increase  in  the  amount  of  sweat  secreted  is  usually  accompanied 
by  dilatation  of  the  cutaneous  vessels.  It  is,  however,  probable 
that  the  secretion  is  like  the  other  secretions,  e.g.,  the  saliva, 
under  the  direct  action  of  a  special  nervous  apparatus,  in  that 
various  nerves  contain  fibres  which  act  directly  upon  the  cells  of 
the  sweat  glands  in  the  same  way  that  the  chorda  tympani 
contains  fibres  which  act  directly  upon  the  salivary  cells.  The 
nerve  fibres  which  induce  sweating  may  act  independently  of 
the  vaso-motor  fibres,  whether  vaso-dilator  or  vaso-constrictor. 
The  local  apparatus  is  under  control  of  the  central  nervous 
system — sweat  centres  probably  existing  both  in  the  medulla  and 
.spinal  cord — and  may  be  reflexly  as  well  as  directly  excited. 
This  will  explain  the  fact  that  sweat  occurs  not  only  when  the 
^kin  is  red,  but  also  when  it  is  pale,  and  the  cutaneous  circulation 
languid,  as  in  the  sweat  which  accompanies  syncope  or  fainting, 
or  which  immediately  precedes  death. 

(5.)  Absorption  by  the  Skin. — Absorption  by  the  skin  has 
been  already  mentioned,  as  an  instance  in  which  that  process 
is  most  actively  accomplished.  Metallic  preparations  rubbed  into 
the  skin  have  the  same  action  as  when  given  internally,  only  in 
a  less  degree.  Mercury  applied  in  this  manner  exerts  its  specific 
influence  upon  syphilis,  and  excites  salivation ;  potassio-tartrate 
of  antimony  may  excite  vomiting,  or  an  eruption  extending  over 
the  whole  body;  and  arsenic  may  produce  poisonous  effects. 
Vegetable  matters,  also,  if  soluble,  or  already  in  solution,  give 
rise  to  their  peculiar  effects,  as  cathartics,  narcotics,  and  the 
like,  when  rubbed  into  the  skin.  The  effect  of  rubbing  is 
probably  to  convey  the  particles  of  the  matter  into  the  orifices 
of  the  glands  whence  they  are  more  readily  absorbed  than  they 
would  be  through  the  epidermis.  When  simply  left  in  contact  with 
the  skin,  substances,  unless  in  a  fluid  state,  are  seldom  absorbed. 

It  has  long  been  a  contested  question  whether  the  skin  covered 
with  the  epidermis  has  the  power  of  absorbing  water ;  and  it  is  a 
point  the  more  difficult  to  determine  because  the  skin  loses  water 
hy  evaporation.     But,  from  the  result   of  many  experiments,  it 


chap,  xin.]  THE    KIDNE1  427 

garded  ai  a  well-ascertained  fact  that  such  absorp- 
tion really  occurs.  The  absorption  of  water  by  the  surface  of  the 
body  may  take  place  in  the  lower  anhnaln  ?ery  rapidly.  Not 
only  frogs,  which  have  a  thin  skin,  but  lizards,  in  which  the 
cuticle  is  thicker  than  in  man,  after  having  loei  reight  by  I 
kept  for  some  time  in  a  dry  atmosphere,  were  found  to  re- 
both  their  weight  and  plumpness  very  rapidly  when  immersed  in 
water.  When  merely  the  tail,  posterior  extremities,  and  posterior 
part  of  the  body  of  the  lizard  were  immersed,  the  wat  ribed 

stributed  throughout  the  system.  And  a  like  absorption 
through  the  skin,  though  to  a  less  extent,  may  take  place  also 
in  man. 

In  severe  cases  of  dysphagia,  when  not  even  fluids  can  be  taken 
into  the  stomach,  immersion  in  a  bath  of  warm  water  or  of  milk 
and  water  may  assuage  the  thirst  :  and  it  has  been  found  in  such 
cases  that  the  weight  of  the  body  is  increased  by  the  immersion. 
rs  also,  when  destitute  "f  fresh  water,  find  their  urgent  thirst 
allayed  by  soaking  their  clothes  in  salt  water  and  wearing  them 
in  that  state  ;  but  these  effects  are  in  part  due  to  the  hindrance  to 
the  evaporation  of  water  from  the  skin. 

(6.)  Regulation  of  Temperature. — For  an  account  of   this 
important  function  of  the  skin,  see  Chapter  on  Animal  Heat. 


CHAPTER    XIII. 

THE   KIDNEYS   AND   THE   EXCRETION   OF   UETXE. 

The  Kidneys  are  two  in  number,  and  are  situated  deeply  in 
the  lunibar  region  of  the  abdomen,  on  either  side  of  the  spinal 
column,  behind  the  peritoneum.  They  correspond  in  position 
to  the  last  two  dorsal  and  two  upper  lumbar  verte  ;  -he  right 
being  slightly  lower  than  the  left  in  consequence  of  the  position 
<-f  the  liver  on  the  right  side  of  the  abdomen.  They  are  character 
istic  in  shape,  about  4  inches  long,  2^  inches  broad,  and  1^  inch 
thick.     The  weight  of  each  kidney  is  about  4  j 


428 


TEE    KIDNEYS. 


[CHAP.  XIII. 


Structure  of  the  Kidneys. — The  kidney  is  covered  by  a 
rather  tough  fibrous  capsule,  which  is  slightly  attached  by  its 
inner  surface  to  the  proper  substance  of  the  organ  by  means  of 
very  fine  fibres  of  areolar  tissue  and  minute  blood-vessels.  From 
the  healthy  kidney,  therefore,  it  may  be  easily  torn  off  without 

injury  to  the  subjacent  corti- 
cal portion  of  the  organ.  At 
the  hilus  or  notch  of  the  kid- 
ney, it  becomes  continuous 
with  the  external  coat  of  the 
upper  and  dilated  part  of  the 
ureter  (fig.  238). 

On  making  a  section  length- 
wise through  the  kidney  (fig. 
238)  the  main  part  of  its  sub- 
stance is  seen  to  be  composed 
of  two  chief  portions,  called 
respectively  the  cortical  and 
the  medullary  portion,  the 
latter    being   also    sometimes 


called  the  pyramidal  portion, 
from  the  fact  of  its  being 
composed  of  about  a  dozen 
conical  bundles  of  urine-tube  . 
each  bundle  being  called  a 
pyramid.  The  upper  part  of 
the  duct  of  the  organ,  or  the 
■ureter,  is  dilated  into  what  is 


Plan  of  a  longitudinal  section  through 
the -pelvis  and  suhstanct  of  the  right  hid 
h;  n,  the  cortical  substance;  b,  b,  broad 
part  of  the  pyramids  of  Malpighi ;  c,  c, 
the  divisions  of  the  pelvis  named  calyces, 
laid  open ;  «•',  one  of  those  unopened  ; 
<l,  summit  of  the  pyramids  of  papilke  pro- 
jecting- into  calyces  ;  e,  e,  section  of  the 
narrow  part  of  two  pyramids  near  the 
calyces ;  p,  pelvis  or  enlarged  divisions 
of  the  ureter  within  the  kidney  ;  u,  the 
ureter  ;  «,  the  sinus  ;  h,  the  hilus. 


called  the  pelvis  of  the  kidney  ; 
and  this,  again,  after  separating  into  two  or  three  principal  divisions, 
is  finally  subdivided  into  still  smaller  portions,  varying  in  number 
from  about  8  to  12,  or  even  more,  and  called  calyces.  Each  of 
these  little  calyces  or  cups,  which  are  often  arranged  in  a  double 
row,  receives  the  pointed  extremity  or  papilla  of  a  pyramid. 
Sometimes,  however,  more  than  one  papilla  is  received  by  a  calyx. 
The  kidney  is  a  compound  tubular  gland,  and  both  its  cortical 
and  medullary  portions  are  composed  essentially  of  secreting 
tubes,  the  tubuli  uriniferi,  which,  by  one  extremity,  in  the  cortical 
portion,  end  commonly  in  little  saccules  containing  blood-vessels- 


OHAP.   xl-ii.J 


STRUCTURE    OF    KIDNEY, 


429 


called  Mcdpighian  bodies,  and,  by  the  other,  open  through  the 
papilla  into  the  pelvis  of  the  kidney,  and  thus  discharge  the  urine 
which  flows  through  them. 

In  the  pyramids  the  tubes  are  chiefly  straight — dividing  and 
diverging  as  they  ascend  through  these 
into  the  cortical  portion;  while  in  the 
latter  region  they  spread  out  more 
irregularly,  and  become  much  branched 
and  convoluted, 

Tubuli  Uriniferi. — The  tubuli  uri- 
niferi  (fig.  239)  are  composed  of  a  nearly 
homogeneous  membrane,  and  are  lined 
internally  by  epithelium.  They  vary 
considerably  in  size  in  different  parts 
of  their  course,  but  are,  on  an  average, 
about  . '  of  an  inch  in  diameter,  and 
are  found  to  be  made  up  of  several 
distinct  sections  which  differ  from  one 
another  very  markedly,  both  in  situa- 
tion and  structure.  According  to  Klein, 
the  following  segments  may  be  made 
out :  (1)  The  Mcdpighian  corpuscle  (figs. 

240,  241),  composed  of  a  hyaline  membrana  propria,  thickened  by 
a  varying  amount  of  fibrous  tissue,  and  lined  by  flattened  nucleated 
epithelial  plates.  This  capsule  is  the  dilated  extremity  of  the 
uriniferous  tubule,  and  contains  within  it  a  glomerulus  of  convo- 
luted capillary  blood-vessels  supported  by  connective  tissue,  and 
covered  by  flattened  epithelial  plates.  The  glomerulus  is  con- 
nected with  an  efferent  and  an  afferent  vessel.  (2)  The  con- 
stricted neck  of  the  capsule  (fig.  240,  2),  lined  in  a  similar  manner, 
connects  it  with  (3)  The  Proximal  convoluted  tubule,  which 
forms  several  distinct  curves  and  is  lined  with  short  co  uninar 
cells,  which  vary  somewhat  in  size.  The  tube  next  passes  almost 
vertically  downwards,  forming  (4)  The  Spiral  tubule,  which  is  of 
much  the  same  diameter,  and  is  lined  in  the  same  way  as  the  con- 
voluted portion.  So  far  the  tube  has  been  contained  in  the  cortex 
of  the  kidney,  it  now  passes  vertically  down  ward  through  the  most 
external  part  (boundary  layer)  of  the  Malpighian  pyramid  into  the 
more  internal  part  (papillary  layer),   where    it    curves  up  sharply, 


Fig.  239. — a.  Portion  of  <<  secreting 
tubule  from  the  cortical  subatana 
of  the  kidney,    b.  The  epithelial 

or  gland-cells.     X  700  times. 


430 


THE    KIDNEYS    AND    URIXE. 


[CHAP.  XIII. 


Re  210  —A  Diagram  of  (h*  sections  of  uriniferous  tubes.  A,  Cortex  limited  externally  by 
C'the  capsule;  a,  subcapsular  lav'er  not  containing  Malpighian  corpuscles;  a  inner 
stratum  of  cortex,  also  without  Malpighian  capsule*  ;  B  Boundary  layer  ;  C,  Papular> 
part  next  the  boundary  layer  ;  i,  Bowman's  capsule  of  Malpighian  corpuscle <;  2,  neck 
of  capsule;  3 .  proximal  convoluted  tubule  ;  4,  spiral  tubule  of  Schaehowa;  5,  descending- 
limb  of  Henle's  loop;  6,  the  loop  proper;  "-thick  part  of  the  ascending  hmb  8. 
spiral  part  of  ascending  limb ;  9,  narrow  ascenduig  hmb  in  ^ ^^^  ™J, '  *°' 
the  irregular  tubule ;  11,  the  intercalated  section  of  ^ei8g«^d^^^111{Lonf 
voluted°tubule  ;  12,  the  curved  coUecting  tubule ;  13,  th%strai?MAr?°TU.ec^/1^^cS! 
the  medullarvrav;  14,  the  collecting  tube  of  the  boundary  k^;,1*  ^^du°i 
lecting  tube  6f  the  papillary  part  which,  pining  with  similar  tubes,  forms  the  duct. 
■Klein  and  Noble  Smith.) 


ell  LP.   Kill.] 


STRUCTURE    OF    KIDNEY. 


43' 


forming  altogether  tl»r  (5  and  6)  Loop  of  ffenle,  which  is  a  wn 
narrow  tube  Lined  with  Battened  nucleated  cells.     PaBsing  n 
oally  upwards  just  us  the  tube  reaches  the  boundary  layer  (7)  it 


HUMP        W  #,' 


Fig.  241. — From  a  vertical  section  through  the  kidney  of  a  dog — the  capsule  of  which  18  sup- 
posed to  be  on  the  right,  a.  The  capillaries  of  the  Malpighian  corpuscle — viz.,  the 
glomerulus,  are  arranged  in  lobules  ;  n,  neck  of  capsule  ;  c,  convoluted  tubes  cut  in 
various  directions ;  b,  irregular  tubule ;  d,  e,  and  /,  are  straight  tubes  running  towar 7  - 
capsules  forming  a  so-called  medullary  ray ;  d,  collecting  tube ;  e,  spiral  tube ;  /,  narrow 
section  of  ascending  limb.     X  380.     (Klein  and  Noble  Smith.) 

suddenly  enlarges  and  becomes  lined  with  polyhedral  cells.  (8) 
About  midway  in  the  boundary  layer  the  tube  again  narrows, 
forming  the  ascending  spiral  of  Rentes  loop,  but  is  still  lined  with 
polyhedral  cells.  At  the  point  where  the  tube  enters  the  cortex, 
(9)  the  ascending  limb  narrows,  but  the  diameter  varies  consider- 
ably ;  here  and  there  the  cells  are  more  flattened,  but  both  in  thU 
as  in  (8),  the  cells  are  in  many  places  very  angular,  branched,  and 
imbricated.  It  then  joins  (10)  the  "  irregular  tubule"  which  has 
a  very  irregular  and  angular  outline,  and  is  lined  with  angular 
and  imbricated  cells.  The  tube  next 'becomes  convoluted,  (n) 
forming  the  distal  convoluted  tube  or  intercalated  section  of  Schiveigger 


432 


THE    IvIDXEYS    AXD    URIXE. 


[chap.  xnr. 


:tW 


P^-Sr  ~ 


Fig.  242. — Transverse  section  of  a  renal  papilla ;  a,  larger 
tubes  or  papillary  ducts  ;  b,  smaller  tubes  of  Henle  ; 
c,  blood-vessels,  distinguished  by  their  flatter  epithe- 
lium ;  d,  nuclei  of  the  stroma  (Kolliker).     x  300. 


Seidel,  which  is  identical  in  all  respects  with  the  proximal  convo- 
luted  tube  (12    and    13).     The    curved    and   straight   collecting 

tubes,  the  former  en- 
tering the  latter  at 
right  angles,  and  the 
latter  passing  verti- 
cally downwards,  are 
lined  with  pol}dicdral, 
or  spindle-shaped,  or 
flattened,  or  angular 
cells.  The  straight 
collecting  tube  now 
enters  the  boundary 
layer  (14),  and  passes 
on  to  the  papillary 
layer,  and,  joining 
with  other  collecting 
tubes,  form  larger 
tubes,  which  finally 
open  at  the  apex  of 
the  papilla.  These  collecting  tubes  are  lined  with  trans'parent 
nucleated  columnar  or  cubical  cells  (14,  15,  16). 

The  cells  of  the  tubules  with  the 
exception  of  Henle's  loop  and  all 
parts  of  the  collecting  tubules,  are, 
as  a  rule,  possessed  of  the  intra- 
nuclear as  well  as  of  the  intra-cellu- 
lar  network  of  fibres,  of  which  the 
vertical  rods  are  most  conspicuous 
parts. 

Heidenhain  observed  that  indigo- 
sulphate  of  sodium,  and  other  pig- 
ments injected  into  the  jugular  vein 
of  an  animal,  were  apparently  ex- 
creted by  the  cells  which  possessed 
pighian  body,  forming  the  termi-     these  rods,  and  therefore  concluded 

nation  of  and  continuous  with  t,       ,  -,      .    ,  ■■  .  , -i  ■»     ,  -i 

the uriniferous tube;  <f,  s, efferent     that  the  pigment  passes  through  the 
pES  ;f  s^rrouSf  ?he"tu£:     cells,  rods,  and  nucleus  themselves. 

^SS^I±4     Klehl>    however    believes    that   the 


Fig.  243. — Diagram  showing  the  rela- 
tion of  the  Malpighian  body  to  tin 
uriniferous  ducts  and  blood-vest  ■. 
a,  one  of  the  interlobular  arteries  ; 
a',  afferent  artery  passing  into  the 
glomerulus  ;  c,  capsule  of  the  Mai- 


CHAP.  Kill.]  BLOOD-VESSELS   OF    KIDNEY.  433 

pigment   passes   through    the    intercellular  substances,  and  not 
through  the  cells. 

In  sonic  places,  it  is  Btated  that  a  distinct  membrane  of  flattened 
cells  can  be  made  out  lining  the  lumen  of  the  tubes  (centrol/ubular 
ni'  mJbrane). 

Blood-vessels  of  Kidney. — In  connection  with  the  general 
distribution  of  blood-vessels  to  the  kidney,  the  Malpighian  Cor- 
puseles  may  be  further  considered.  They  (fig.  243)  are  found  only 
in  the  cortical  part  of  the  kidney,  and  are  confined  to  the  central 
part,  which,  however,  makes  up  about  seven-eighths  of  the  whole 
cortex.  <  Mi  a  section  of  the  organ,  some  of  them  are  just  visible 
to  the  naked  eve  as  minute  red  points;  others  are  too  small  to  be 
thus  seen.  Their  average  diameter  is  about  y—  of  an  inch.  Eacli 
of  them  is  composed,  as  we  have  seen  above,  of  the  dilated  ex- 
tremity of  an  urinary  tube,  or  Malpighian  capsule,  enclosing  a  tuft 
of  blood-vessels. 

The  renal  artery  divides  into  several  branches,  which,  passing 
in  at  the  hilus  of  the  kidney,  and  covered  by  a  fine  sheath  of 
areolar  tissue  derived  from  the  capsule,  enter  the  substance  of  the 
organ  in  the  intervals  between  the  papilhe,  chiefly  at  the  junction 
between  the  cortex  and  the  boundary  layer.  The  chief  branches 
then  pass  almost  horizontally,  giving  off  smaller  branches  up- 
wards to  the  cortex  and  downwards  to  the  medulla.  The  former 
are  for  the  most  part  straight,  they  pass  almost  vertically  to  the 
surface  of  the  kidney,  giving  off  laterally  in  all  directions  longer 
or  shorter  branches,  which  supply  the  afferent  arteries  to  the 
Malpighian  bodies. 

The  small  afferent  artery  (figs.  243  and  245)  which  enters 
the  Malpighian  corpuscle,  breaks  up  as  before  mentioned  in 
the  interior  into  a  dense  and  convoluted  and  looped  capil- 
lary plexus,  which  is  ultimately  gathered  up  again  into  a 
single  small  efferent  vessel,  comparable  to  a  minute  vein, 
which  leaves  the  Malpighian  capsule  just  by  the  point  at 
which  the  afferent  artery  enters  it.  On  leaving,  it  does  not 
immediately  join  other  small  veins  as  might  have  been  ex- 
pected, but  again  breaking  up  into  a  network  of  capil- 
lary vessels,  is  distributed  on  the  exterior  of  the  tubule,  from 
whose  dilated  end  it  had  just  emerged.  After  this  second 
breaking  up  it  is   finally  collected  into  a  small  vein,  which,  by 

F   F 


434 


THE  KIDNEYS  AND   URINE. 


[chap.  XIII. 


union  with  others  like  it,  helps  to  form  the  radicles  of  the  renal 


rem. 


Thus,  in  the  kidney,  the  blood  entering  by  the  renal  artery 
traverses  two  sets  of  capillaries  before  emerging  by  the  renal  vein, 
an  arrangement  which  may  be  compared  to  the  portal  system  in 
miniature. 

The  tuft  of  vessels  in  the  course  of  development  is,  as  it  were 
thrust  into  the  dilated  extremity  of  the  urinary  tubule,  which 
finally  completely  invests  it  just  as  the  pleura  invests  the  lungs 
or  the  tunica  vaginalis  the  testicle.  Thus  the  Malpighian  capsule 
is  lined  by  a  parietal  layer  of  squamous  cells  and  a  visceral  or 
reflected  layer  immediately  covering  the  vascular  tuft  (fig.  241), 
and  sometimes  dipping  down  into  its  interstices.  This  reflected 
layer  of  epithelium  is  readily  seen  in  young  subjects,  but  cannot 
always   be   demonstrated   in    the   adult.       (See    figs.    244    and 

245-) 


Fig.  244. —  Transverse  section  of  a  developing  JIalpighian  capsule  and  tuft  (human)  X  300. 
From  a  foetus  at  about  the  fourth  month;  a,  flattened  cells  growing  to  form  the 
capsule ;  b,  more  rounded  cells,  continuous  with  the  above,  reflected  round  c,  and, 
finally  enveloping  it ;  c,  mass  of  embryonic  cells  which  will  later  become  developed 
into  blood-vessels  ( W.  Pye) . 


The  vessels  which  enter  the  medullary  layer  break  up  into 
smaller  arterioles,  which  pass  through  the  boundary  layer  and 
proceed  in  a  straight  course  between  the  tubules  of  the  papillary 
layer,  giving  off  on  their  way  branches,  which  form  a  fine  arterial 
meshwork  around  the  tubes,  and  end  in  a  similar  plexus,  from 
which  the  venous  radicles  arise. 


CHAP.  XIII.] 


STRUCTURE  OF  THE  URETERS. 


435 


Besides  the  small  afferent  arteries  of  the  Malpighian  bodies, 
there  are,  of  course,  others  which  are  distributed  in  the  ordinary 
manner,  for  nutrition's  sake,  to  the  different  parts  of  the  organ  ; 
and  in  the  pyramids,  between  the  tubes,  there  are  numerous 
straight  vessels,  the  vasta  recta,  supposed  by  some  observers  to  be 


Fig.  245.— Epithelial  elements  of  a  Malpighian  capsule  and  tuft,  with  the  commence- 
ment of  a  urinary  tubule  showing  the  afferent  and  efferent  vessel ;  a,  layer  of 
tesselated  epithelium  forming'  the  capsule;  b,  similar,  but  rather  larger  epithelial 
cells,  placed  in  the  walls  of  the  tube;  c,  cells,  covering  the  vessels  of  the  capil- 
lary tuft;  d,  commencement  of  the  tubule,  somewhat  narrower  than  the  rest  of  it 
(W.  Pye). 


branches  of  vasa  efferentia  from  Malpighian  bodies,  and  therefore 
comparable  to  the  venous  plexus  around  the  tubules  in  the 
cortical  portion,  while  others  think  that  they  arise  directly  from 
small  branches  of  the  renal  arteries. 

Between  the  tubes,  vessels,  etc.,  which  make  up  the  substance 
of  the  kidney,  there  exists,  in  small  quantity,  a  fine  matrix  of 
areolar  tissue. 

Nerves. — The  nerves  of  the  kidney  are  derived  from  the  renal 
plexus. 

Structure  of  the  Ureters. — The  duct  of  the  kidney,  or  ureter, 
is  a  tube  about  the  size  of  a  goose-quill,  and  from  a  foot  to  sixteen 
inches  in  length,  which,  continuous  above  with  the  pelvis  of  the 

F   F   2 


4.36  THE   KIDXETS  AND   URINE.  [chap.  xiii. 

kidney,  ends  below  by  perforating  obliquely  the  walls  of  the 
bladder,  and  opening  on  its  internal  surface.  It  is  constructed  of 
three  principal  coats  (a)  an  outer,  tough,  firms  and  elastic 
coat ;  (h)  a  middle,  muscular  coat,  of  which  the  fibres  are  unstriped, 
and  arranged  in  three  layers — the  fibres  of  the  central  layer  being 
circular,  and  those  of  the  other  two  longitudinal  in  direction ;  and 
(c)  an  internal  mucous  lining  continuous  with  that  of  the  pelvic 
of  the  kidney  above,  and  of  the  urinary  bladder  below.  The 
epithelium  of  all  these  parts  (fig.  246)  is  alike  stratified  and  of 
a  somewhat  peculiar  form ;  the  cells  on  the  free  surface  of  the 
mucous  membrane  being  usually  spheroidal  or  polyhedral  with 
one  or  more  spherical  or  oval  nuclei  ;  while  beneath  these  are 
pear-shaped  cells,  of  which  the  broad  ends  are  directed  to- 
wards the  free  surface,  fitting  in  beneath  the  cells  of  the  first 
row,  and  the  apices  are  prolonged  into  processes  of  various 
lengths,  among  which,  again,  the  deepest  cells  of  the  epithe- 
lium are  found  spheroidal,  irregularly  oval,  spindle-shaped  or 
conical. 

Structure  of  Urinary  Bladder. — The  urinary  bladder,  which 
forms  a  receptacle  for  the  temporary  lodgment  of  the  urine  in  the 
intervals  of  its  expulsion  from  the  body,  is  more  or  less  pyrifornu 
its  widest  part,  which  is  situate  above  and  behind,  being  termed 
the  fundus  :  and  the  narrow  constricted  portion  in  front  and 
below,  by  which  it  becomes  continuous  with  the  urethra,  being- 
called  its  cervix  or  neck.  It  is  constructed  of  four  principal  coatsr 
— serotiSj  muscular,  areolar  or  submucous,  and  mucous,  (a)  The 
serous  coat,  which  covers  only  the  posterior  and  upper  half  of  the 
bladder,  has  the  same  structure  as  that  of  the  peritoneum,  with 
which  it  is  continuous,  (b)  The  fibres  of  the  muscular  coat, 
which  are  unstriped,  are  arranged  in  three  principal  layers,  of 
which  the  external  and  internal  (Ellis)  have  a  general  longitudinalr 
and  the  middle  layer  a  circular  direction.  The  latter  are  especi- 
ally developed  around  the  cervix  of  the  organ,  and  are  described  as 
forming  a  sphincter  vesicae.  The  muscular  fibres  of  the  bladder, 
like  those  of  the  stomach,  are  arranged  not  in  simple  circles,  but 
in  figure-of-8  loops,  (c)  The  areolar  or  submucous  coat  is  con- 
structed of  connective  tissue  with  a  large  proportion  of  elastic 
fibres,  (d)  The  mucous  membrane,  which  is  rugose  in  the  con- 
tracted state  of  the  organ,  does  not   differ  in  essential  structure 


<   SAP.    XIII.] 


THE   URINE, 


437 


from  mucous  membranes  in  general     Its  epithelium  is  stratified 
and  closely  resembles  that  of  the  pelvis  of  the  kidney  and  the 

ureter  (tig.  246). 


Fig.  246.— Bpi&di 'um  of  th*  Madder;  a,  one  of  the  cells  of  the  first  row;  b,  a  cell  of  the 
second  row  ;  c,  cells  in  situ,  of  first,  second,  and  deepest  layers  (Obersteiner). 

The  mucous  membraue  is  provided  with  mucous  glauds,  which 
are  more  numerous  near  the  neck  of  the  bladder. 

The  bladder  is  well  provided  with  blood-  and  lymph-vessels, 
and  with  nerves.  The  latter  are  branches  from  the  sacral  plexus 
(spinal)  and  hypogastric  plexus  (sympathetic).  A  few  ganglion- 
cells  are  found,  here  and  there,  in  the  course  of  the  nerve-fibres. 


The  Excretion  of  the  Kidney :— The  Urine. 

Physical  Properties. — Healthy  urine  is  a  perfectly  transparent, 
amber-coloured  liquid,  with  a  peculiar,  but  not  disagreeable  odour, 
a  bitterish  taste,  and  slight  acid  reaction.  Its  specific  gravity 
varies  from  to  15  to  1025.  On  standing  for  a  short  time,  a  little 
mucus  appeai-s  in  it  as  a  flocculent  cloud. 

Chemical  Composition.  —  The  urine  consists  of  water, 
holding  in  solution  certain  organic  and  saline  matters  as 
its  ordinary  constituents,  and  occasionally  various  matters 
taken  into  the  stomach  as  food — salts,  colouring  matter,  and  the 
like. 


438 


THE  KIDNEYS  AND  URINE. 


[chap.  xnr. 


Table  of   the   Chemical   Composition   of   the    Urine   (modified 

from  becquerel). 


Water 

Urea 

Other  nitrogenous  crystalline  bodies — 

Uric  acid,  principally  in  the  form  of  alka- 
line urates,  a  trace  only  free. 
Kreatinin,  xanthin.  hypoxanthin. 
Hippuric    acid,   leucin,    tyrosin.   taurin, 
cystin,  &c,  all  in  small  amounts  and 
not  constant. 
Mucus  and  pigment. 

Salts  :— 

Inorganic — 

Principally  sulphates,  phosphates,  and 
chlorides  of  sodium,  and  potassium, 
with  phosphates  of  magnesium  and 
calcium,  traces  of  silicates  and  of  chlo- 
rides. 

Organic- — 

Lactates,  hippurates,  acetates  and  for- 
mates, which  only  appear  occasionally. 


967 
14230 


10-635 


3-135 


Sugar 


a  trace  sometimes. 


Gases  (nitrogen  and  carbonic  acid  principally). 


1000 


Reaction  of  the  Urine. — The  normal  reaction  of  the  urine  is 
slightly  acid.  This  acidity  is  due  to  acid  phosphate  of 
sodium,  and  is  less  marked  after  meals.  The  urine  contains 
no  appreciable  amount  of  free  acid,  as  it  gives  no  precipitate 
with  sodium  hyposulphite.  After  standing  for  some  time  the 
acidity  increases  from  a  kind  of  fermentation,  due  in  all  proba- 
bility to  the  presence  of  mucus,  and  acid  urates  or  free  uric 
acid  is  deposited.  After  a  time,  varying  in  length  according  to 
the  temperature,  the  reaction  becomes  strongly  alkaline  from  the 
change  of  urea  into  ammonium  carbonate — while  at  the  same  time 
a  strong  ammoniacal  and  foetid  odour  appears,  with  deposits  of 
triple  phosphates  and  alkaline  urates.  As  this  does  not  occur 
unless  the  mine  is  exposed  to  the  air,  or,  at  least,  until  air  has 
had  access  to  it,  it  is  probable  that  the  decomposition  is  due  to 
atmospheric  germs. 

Reaction  of  Urine  in  different  classes  0/  Animals. — In  most  herbivorous 


OHAP.  xiii.]  TIN:    I'KIXE.  439 

:inim:ils  the  mine  is  alkaline  and  turbid.  The  difference  depends,  not  on 
any  peculiarity  in  the  mode  of  seeivt  ion,  hut  on  the  differences  in  the  food 
on  which  the  two  classes  Bubsist:  for  when  carnivorous  animals,  such  as 
dogs,  an-  restricted  to  a  vegetable  diet, their  urine  becomes  pale,  turbid,  and 
alkaline,  like  that  of  an  herbivorous  animal,  hut  resumes  in  former  acidity 
on  tin-  return  to  an  animal  diet;  while  the  urine  voided  by  herbivorous 
animals,  e.g.,  rabbits,  fed  for  some  time  exclusively  upon  animal  .suhstanees, 
presents  the  acid  reaction  and  other  qualities  of  the  urine  of  Carnivora,  its 
ordinary  alkalinity  being  restored  only  on  the  substitution  of  a  vegetable  for 
the  animal  diet.  Human  urine  is  not  usually  rendered  alkaline  by  vegetable 
diet,  but  it  becomes  so  after  the  free  use  of  alkaline  medicines,  or  of  the 
alkaline  salts  with  carbonic  or  vegetable  acids  ;  for  these  latter  are  changed 
into  alkaline  carbonates  previous  to  elimination  by  the  kidneys. 

Average  quantity  of  the  chief  constituents  of  the  Urine 
excreted  in  24  hours  by  healthy  male  adults  (Parkes). 

Water 52*      fluid  ounces. 

Urea 512*4    grains. 

Uric  acid 8*5         .. 

Hippurie  acid,  uncertain  probably  10  to  15. 

Sulphuric  acid      .......       31*11 

Phosphoric  acid 45- 

Potassium,  Sodium,  and  Ammonium  Chlorides  1 

and  free  Chlorine j  3  3    5 

Lime         ...  3-5 

Magnesia      ........        y  ., 

Mucus 7-  n 

(Kreatinin        \ 

Extractives    kiSm?nt 
Xanthm 

VHypoxanthin  f  54        ;» 

Resinous  matter, 

&c.  j 

Variations  in  Quantity  of  Constituents. — From  these  pro- 
portions, however,  most  of  the  constituents  are,  even  in  health, 
liable  to  variations.  The  variations  of  the  water  in  different 
seasons,  and  according  to  the  quantity  of  drink  and  exer- 
cise, have  already  been  mentioned.  The  water  of  the  urine 
is  also  liable  to  be  influenced  by  the  condition  of  the  ner- 
vous system,  being  sometimes  greatly  increased  in  hysteria, 
and  some  other  nervous  affections  ;  and  at  other  times  diminished. 
In  some  diseases  it  is  enormously  increased  ;  and  its  increase 
may  be  either  attended  with  an  augmented  quantity  of 
solid  matter,  as  in  ordinary  diabetes,  or  may  be  nearly  the  sole 
change,  as  in  the   affection  termed  diabetes  insipidus.     In  other 


440  THE  KIDNEYS  AND   URINE.  [chap.  xiii. 

diseases,  e.g.,  the  various  forms  of  albuminuria,  the  quantity  may 
be  considerably  diminished.  A  febrile  condition  almost  always 
diminishes  the  quantity  of  water  ;  and  a  like  diminution  is  caused 
by  any  affection  which  draws  off  a  large  quantity  of  fluid  from  the 
body  through  any  other  channel  than  that  of  the  kidneys,  e.g.,  the 
bowels  or  the  skin. 

Method  of  estimating  the  Solids. — A  useful  rule  for  approximately  esti- 
maling  the  total  solids  in  any  given  specimen  of  healthy  urine  is  to  multiply 
the  last  two  figures  representing  the  specific  gravity  by  2*33.  Thus,  in  urine 
of  sp.  gr.  1025,  2'33  x  25  =  58*25  grains  of  solids,  are  contained  in  1000  grains 
of  the  urine.  In  using  this  method  it  must  be  remembered  that  the  limits 
of  error  are  much  wider  in  diseased  than  in  healthy  urine. 

Variations  in  the  Specific  Gravity. — The  specific  gravity  of 
the  human  urine  is  about  1020.  Probably  no  other  animal  fluid 
presents  so  many  varieties  in  density  within  twenty-four  hours  as 
the  urine  does  ;  for  the  relative  quantity  of  water  and  of  solid 
constituents  of  which  it  is  composed  is  materially  influenced  by  the 
condition  and  occupation  of  the  body  during  the  time  at  which  it 
is  secreted,  by  the  length  of  time  which  has  elapsed  since  the  last 
meal,  and  by  several  other  accidental  circumstances.  The  exist- 
ence of  these  causes  of  difference  in  the  composition  of  the  urine 
has  led  to  the  secretion  being  described  under  the  three  heads  of 
urina  sanguinis,  urina  potus,  and  urina  cibi.  The  first  of  these 
names  signifies  the  urine,  or  that  part  of  it,  which  is  secreted 
from  the  blood  at  times  in  which  neither  food  nor  drink  has  been 
recently  taken,  and  is  applied  especially  to  the  urine  which  is 
evacuated  in  the  morning  before  breakfast.  The  terms  urina 
potus  indicates  the  urine  secreted  shortly  after  the  introduction  of 
any  considerable  quantity  of  fluid  into  the  body  :  and  the  urina 
cili,  the  portions  secreted  during  the  period  immediately  suc- 
ceeding a  meal  of  solid  food.  The  last  kind  contains  a  larger 
quantity  of  solid  matter  than  either  of  the  others  ;  the  first  or 
second,  being  largely  diluted  with  water,  possesses  a  comparatively 
low  specific  gravity.  Of  these  three  kinds,  the  morning  urine  is  the 
best  calculated  for  analysis  in  health,  since  it  represents  the 
simple  secretion  unmixed  with  the  elements  of  food  or  drink ;  if 
it  be  not  used,  the  whole  of  the  urine  passed  during  a  period  of 
twenty-four  hours  should  be  taken.  In  accordance  with  the 
various    circumstances   above-mentioned,   the    specific  gravity  of 


i  hap.  xin.]  THE  PEINE.  441 

the  urine  may,  consistently  with  health,  range  widely  on  both 
ndee  of  the  usual   average.     The  average  healthy  range  may  be 

ted  at  from   101 5  in  the  winter  to    1025  in  the  summer  \  but 
variations  of  diet  and  exercise,  and   many  other  circumstam 
may  make  even  greater  differences  than  these.      In  di  the 

variation  may  be  greater  :  sometimes  descending,  in  albuminuria, 
to  1004,  and  frequently  ascending  in  diabetes,  when  the  urine 
is  loaded  with  sugar,  to  1050,  or  even  to  1060. 

Quantity. — The  total  quantity  of  urine  passed  in  twenty-four 
hours  is  affected  by  numerous  circumstances.  Ou  taking  the 
mean  of  many  observations  by  several  experimenters,  the  average 
quantity  voided  in  twenty-four  hours  by  healthy  male  adults 
from  20  to  40  years  of  age  has  been  found  to  amount  to  about 
52 \  fluid  ounces  ( 1 J  to  2  litres). 

Abnormal  Constituents. — In  disease,  or  after  the  ingestion 
of  special  foods,  various  abnormal  substances  occur  in  urine,  of 
which  the  following  may  be  mentioned — serum-albumin,  globulin, 
ferments  (apparently  present  in  health  also),  blood,  sugar,  bile 
acids,  and  pigments,  fats,  oxalates,  various  salts  taken  as  medicine, 
and  other  matters,  as  bacteria  and  renal  casts. 


The  Solids  of  the  Urine. 

Urea. — (CH4N20.) — Urea  is  the  principal  solid  constituent  of 
the  urine,  forming  nearly  one-half  of  the  whole  quantity  of  solid 
matter.  It  is  also  the  most  important  ingredient,  since  it  is  the 
chief  substance  by  which  the  nitrogen  of  decomposed  tissue  and 
superfluous  food  is  excreted  from  the  body.  For  its  removal,  the 
secretion  of  urine  seems  especially  provided  ;  and  by  its  retention 
in  the  blood  the  most  pernicious  effects  are  produced. 

Properties. — Urea,  like  the  other  solid  constituents  of  the 
urine,  exists  in  a  state  of  solution.  But  it  may  be  procured  in  the 
solid  state,  and  then  appears  in  the  form  of  delicate  silvery  acicular 
crystals,  which,  under  the  microscope,  appear  as  four-sided  prisms 
(fig.  247).  It  is  obtained  in  this  state  by  evaporating  urine  care- 
fully to  the  consistence  of  honey,  acting  on  the  inspissated  mass 
with  four  parts  of  alcohol,  then  evaporating  the  alcoholic  solution, 
and  purifying  the  residue  by  repeated  solution  in  water  or  alcohol, 
and   finally  allowing   it   to   crystallize.     It   readily  combines  with 


442 


THE   KIDNEYS  AND   URINE. 


[chap.  XIII. 


some  acids,  like  a  weak  base  ;  and  may  thus  be  conveniently 
procured  in  the  form  of  crystals  of  nitrate  or  oxalate  of  urea. 


Fig.  247. — Crystals  of  Urea. 

Urea  is  colourless  when  pure  ;  when  impure,  yellow  or  brown  : 
without  smell,  and  of  a  cooling  nitre-like  taste ;  has  neither  an 
acid  nor  an  alkaline  re-action,  and  deliquesces  in  a  moist  and  warm 
atmosphere.  At  590  F.  (150  C.)  it  requires  for  its  solution  less 
than  its  weight  of  water ;  it  is  dissolved  in  all  proportions  by 
boiling  water ;  but  it  requires  five  times  its  weight  of  cold  alcohol 
for  its  solution.  It  is  insoluble  in  ether.  At  2480  F.  (1200  C.) 
it  melts  without  undergoing  decomposition  ;  at  a  still  higher 
temperature  ebullition  takes  place,  and  carbonate  of  ammonium 
sublimes  ;  the  melting  mass  gradually  acquires  a  pulpy  consist- 
ence ;  and  if  the  heat  is  carefully  regulated,  leaves  a  grey-white 
powder,  cyanic  acid. 

Chemical  Nature  of  Urea. — The  chemical  nature  of  urea  is 
explained  elsewhere,*  but  it  will  be  as  well  to  mention  here  that 
urea  is  isomeric  with  ammonium  cyanate,  and  that  it  was  first 
artificially  produced  from  this  substance.  Thus  : — Ammonium 
cyanate  (NH4.  CNO)  =  urea  (CH  +  N20).  The  action  of  heat 
upon  urea  in  evolving  ammonium  carbonate  and  leaving  cyanic 
acid,  is  thus  explained.  A  similar  decomposition  of  the  urea  with 
development  of  ammonium  carbonate  ensues  spontaneously  when 
urine  is  kept  for  some  days  after  being  voided,  and  explains  the 
ammoniacal  odour  then  evolved  (p.  438).     The  urea  is  sometimes 

*  Appendix. 


CHAP,  xiii.]  UREA.  AA-y 

decomposed  before  it  Leaves  the  bladder,  when  the  mucous  mem 
brane  is  diseased,  and  the  mucus  secreted   by  it  is  both  mop 
abundant,  and,  probably,  more  prone  to  act  as  a  ferment  ;  although 
the  decomposition  does  not  often  occur  unless  atmospheric  g<  ru  a 
have  bad  access  to  the  urine. 

Variations  in  the  Quantity  of  Urea. — The  quantity  of  urea 
excreted  is,  Like  that  of  the  urine  itself,  subject  to  considerable 
variation.  For  a  healthy  adult  500  grains  (about  32*5  grnis. ) 
per  diem  may  be  taken  as  rather  a  high  average.  Its  percentage 
in  healthy  urine  is  1  "5  to  2*5.  It  is  materially  influenced  by  diet, 
being  greater  when  animal  food  is  exclusively  used,  less  when  the 
diet  is  mixed,  and  least  of  all  with  a  vegetable  diet.  As  a  rule, 
men  excrete  a  larger  quantity  than  women,  and  persons  in  the 
middle  periods  of  life  a  larger  quantity  than  infants  or  old  people. 
The  quantity  of  urea  excreted  by  children,  relatively  to  their 
body- weight,  is  much  greater  than  in  adults.  Thus  the  quantity 
of  urea  excreted  per  kilogram  of  weight  was,  in  a  child,  o'8  grm.  : 
in  an  adult  only  0*4  grm.  Regarded  in  this  way,  the  excretion  of 
carbonic  acid  gives  similar  results,  the  proportions  in  the  child 
and  adult  being  as  82  :  34. 

The  quantity  of  urea  does  not  necessarily  increase  and  decrease- 
with  that  of  the  urine,  though  on  the  whole  it  would  seem  that 
whenever  the  amount  of  urine  is  much  augmented,  the  quantity 
of  urea  also  is  usually  increased  ;  and  it  appears  that  the  quantity 
of  urea,  as  of  urine,  may  be  especially  increased  by  drinking  large 
quantities  of  water.  In  various  diseases  the  quantity  is  reduced 
considerably  below  the  healthy  standard,  while  in  other  affections 
it  is  above  it. 

Estimation  of  Urea. — A  convenient  apparatus  for  estimating" 
the  quantity  of  urea  in  a  given  sample  of  urine  is  that  devised 
by  Russell  and  West. 

(Jrea  contains  nearly  half  its  weight  of  nitrogen  ;  hence  this  gas 
may  be  taken  as  a  measure  of  the  urea.  A  small  quantity  of 
urine  is  mixed  with  a  large  excess  of  solution  of  sodium  hypo- 
bromite,  which  completely  decomposes  the  urea,  liberating  all 
the  nitrogen  in  a  gaseous  form  :  a  gentle  heat  promotes  the  re- 
action. The  percentage  of  urea  can  of  course  be  readily  calculated 
from  the  volume  of  nitrogen  evolved  from  a  measured  quantity  of 
the  urine,  but  this  calculation  is  avoided  by  graduating  the  tube 


444  THE  KIDXEYS  AXD   URINE.  [chap,  xiii 

in  which  the  nitrogen  is  collected  with  numbers  which  indicate 
the  corresponding  percentage  of  urea.  C0X2H4  4-  3XaBrO 
+  2XaH0  =  3XaBr  +  3H20  +  Xa2C03  +  X2. 

Uric  Acid  (CjH^N^Og). — This  substance  which  was  formerly 
termed  lithic  acid,  on  account  of  its  existence  in  many  forms  of 
urinary  calculi,  is  rarely  absent  from  the  urine  of  man  or  animals, 
though  in  the  feline  tribe  it  seems  to  be  sometimes  entirely 
replaced  by  urea.  The  proportionate  quantity  of  uric  acid  varies 
considerably  in  different  animals.  In  man,  and  Mammalia 
generally,  especially  the  Herbivora,  it  is  comparatively  small.  In 
the  whole  tribe  of  birds,  and  of  serpents,  on  the  other  hand,  the 
■quantity  is  very  large,  greatly  exceeding  that  of  the  urea.  In 
the  urine  of  granivorous  birds,  indeed,  urea  is  rarely  if  ever  found, 
its  place  being  entirely  supplied  by  uric  acid. 

Variations  in  Quantity. — The  quantity  of  uric  acid,  like  that 
of  urea,  in  human  urine,  is  increased  by  the  use  of  animal  food, 
and  decreased  by  the  use  of  food  free  from  nitrogen,  or  by  an 
exclusively  vegetable  diet.  In  most  febrile  diseases,  and  in 
plethora,  it  is  formed  in  unnaturally  large  quantities :  and  in 
gout  it  is  deposited  in,  and  around,  joints,  in  the  form  of  urate 
of  soda,  of  which  the  so-called  chalk-stones  of  this  disease  are 
principally  composed.  The  average  amount  secreted  in  twenty- 
four  hours  is  8*5  grains  (rather  more  than  half  a  gramme). 

Condition  of  Uric  Acid  in  the  Urine. — The  condition  in 
which  uric  acid  exists  in  solution  in  the  urine  has  formed  the 
subject  of  some  discussion,  because  of  its  difficult  solubility  in 
water.  It  is  found  chiefly  in  the  form  of  urate  of  sodium,  produced 
by  the  uric  acid  as  soon  as  it  is  formed  combining  with  part  of  the 
base  of  the  alkaline  sodium  phosphate  of  the  blood.  Hippuric 
acid,  which  exists  in  human  urine  also,  acts  upon  the  alkaline 
phosphate  in  the  same  way,  and  increases  still  more  the 
quantity  of  acid  phosphate,  on  the  presence  of  which  it  is 
probable  that  a  part  of  the  natural  acidity  of  the  urine  depends. 
It  is  scarcely  possible  to  say  whether  the  union  of  uric  acid  with 
the  base  sodium  and  probably  ammonium,  takes  place  in  the 
blood,  or  in  the  act  of  secretion  in  the  kidney  :  the  latter  is  the 
more  likely  opinion ;  but  the  quantity  of  either  uric  acid  or  urates 
in  the  blood  is  probably  too  small  to  allow  of  this  question  being 
solved. 


OHAP.  xni.]  URIC   ACID.  445 

Owing    to   its  existence   in  combination   in  healthy  urine,    uric 
acid  for  examination  must  generally  be  precipitated  from  its  bases 
by  a  Btronger  acid.     Frequently,  however,  when  excreted  in  ex< 
it  is  deposited  in   a  crystalline  form  (fig.  248),  mixed  with   largi 
quantities  of  ammonium  or  sodium  urate.     In  such  cases  it  may 


Fig".  248. — Various  forms  of  uric  acid  crystals.  Fig.  249. — Crystals  of  hippuric  acid. 

be  procured  for  microscopic  examination  by  gently  warming  the 
portion  of  urine  containing  the  sediment ;  this  dissolves  urate  of 
ammonium  and  sodium,  while  the  comparatively  insoluble  crystals 
of  uric  acid  subside  to  the  bottom. 

The  most  common  form  in  which  uric  acid  is  deposited  in  urine, 
is  that  of  a  brownish  or  yellowish  powdery  substance,  consisting 
of  granules  of  ammonium — or  sodium  urate.  When  deposited  in 
crystals,  it  is  most  frequently  in  rhombic  or  diamond-shaped 
laniinse,  but  other  forms  are  not  uncommon  (fig.  248).  When 
deposited  from  urine,  the  crystals  are  generally  more  or  less 
deeply  coloured,  from  being  combined  with  the  colouring  prin- 
ciples of  the  urine. 

There  are  two  chief  tests  for  uric  acid  besides  the  microscopic 
evidence  of  its  crystalline  structure  :  ( 1 )  The  Murexide  test,  which 
consists  of  evaporating  to  dryness  a  mixture  of  strong  nitric  acid 
and  uric  acid  in  a  water  bath.  This  leaves  a  yellowish-red  residue- 
of  Alloxan  (C4H2N204)  and  urea,  and  this,  on  addition  of  ammo- 
nium hydrate  gives  a  beautiful  purple  (ammonium  purpurater 
C8H.t  (NH4)  N50e),  deepened  on  addition  of  caustic  potash. 
(2)  Schiff's  test.  Dissolve  the  uric  acid  in  sodium  carbonate  solu- 
tion, and  drop  some  of  it  on  a  filter  paper  moistened  with  silver 


446  THE  KIDNEYS  AND  URINE.  [chap.  xiii. 

nitrate,  a  black  spot  appears,  which  corresponds  to  the  reduction 
•of  silver  by  the  uric  acid. 

Hipp-uric  Acid  (C9H9N03)  has  long  been  known  to  exist  in 
the  urine  of  herbivorous  animals  in  combination  with  soda.  It 
.also  exists  naturally  in  the  urine  of  man,  in  quantity  equal  or 
rather  exceeding  that  of  the  uric  acid. 

Pigments. — The  colouring  matters  of  the  urine  are  :  (i)  Uro- 
bilin, a  substance  connected  with  the  colouring  matters  of  the 
blood  and  bile  (p.  341) ;  it  is  especially  seen  in  febrile  urine  and 
.exists  normally,  but  to  less  amount;  it  is  of  a  yellowish-red  colour  ; 
^2)  Uro-chrome,  which  on  exposure  undergoes  oxydation,  and 
becomes  Uro-erytkrin,  the  former  being  yellowish  and  the  latter 
sandy  red ;  and  (3)  Indican  is  occasionally  present. 

Indican  is  not  itself  pigmentary,  though  by  its  decomposition  indigo 
blue  and  indigo  red  are  produced.  Its  presence  can  usually  be  detected  by 
adding  to  a  small  quantity  of  urine  an  equal  bulk  of  strong  hydrochloric 
acid,  and  gently  heating  the  solution  ;  on  the  addition  of  two  or  three  drops 
•of  strong  nitric  acid  a  delicate  purplish  tint  is  developed,  and  indigo  blue 
and  red  crystals  separate  out. 

Mucus. — Mucus  in  the  urine  consists  principally  of  the  epithe- 
lial debris  of  the  mucous  surface  of  the  urinary  passages.  Particles 
of  epithelium,  in  greater  or  less  abundance,  may  be  detected  in 
most  samples  of  urine,  especially  if  it  has  remained  at  rest  for 


Fig.  250. — Mucus  deposited  from  urine. 

some  time  and  the  lower  strata  are  then  examined  (fig.  250).  As 
urine  cools,  the  mucus  is  sometimes  seen  suspended  in  it  as  a 
■delicate  opaque  cloud,  but  generally  it  falls.  In  inflammatory 
affections  of  the  urinary  passages,  especially  of  the  bladder,  mucus 


CHAP,  xiii.]  EXTRACTIVES.  447 

in  large  quantities  is  poured   forth,  and    speedily  undergoes  de- 
composition.    The  presence  of  the  decomposing  mucus  excites  (as 

already  stated,  p.  438)  chemical  changes  in  the  urea,  whereby 
ammonia,  or  carbonate  of  ammonium,  is  formed,  which,  combining 
with  the  excess  of  acid  in  the  super-phosphates  in  the  urine,  pro- 
duces insoluble  neutral  or  alkaline  phosphates  of  calcium  and 
magnesium,  and  phosphate  of  ammonium  and  magnesium.  These 
mixing  with  the  mucus,  constitute  the  peculiar  white,  viscid, 
mortar-like  substance  which  collects  upon  the  mucous  surface  of 
the  bladder,  and  is  often  passed  with  the  urine,  forming  a  thick 
tenacious  sediment. 

Extractives. — Besides  mucus  and  colouring  matter,  urine 
contains  a  considerable  quantity  of  nitrogenous  compounds, 
usually  described  under  the  generic  name  of  extractives.  Of  these, 
the  chief  are:  (1)  Kreatinin  (C4H7N30)  a  substance  derived, 
probably,  from  the  metamorphosis  of  muscular  tissue,  crystallizing 
in  colourless  oblique  rhombic  prisms ;  a  fairly  definite  amount  of 
this  substance,  about  15  grains  (1  grm.),  appears  in  the  urine 
daily,  so  that  it  must  be  looked  upon  as  a  normal  constituent ;  it 
is  increased  on  an  increase  of  the  nitrogenous  constituents  of  the 
food  ;  (2)  Xanthin  (C5N4H402),  an  amorphous  powder  soluble  in 
hot  water ;  (3)  Hypo-xanthin,  or  sarkin  (CgN^H^O)  ;  (4)  Oxaluric 
acid  (CgH^NgO^),  in  combination  with  ammonium;  (5)  AUantoin 
(04H6N403)  in  the  urine  of  the  newr-born  child.  All  these  extrac- 
tives are  chiefly  interesting  as  being  closely  connected  with  urea, 
and  mostly  yielding  that  substance  on  oxidation.  Leucin  and 
tyrosin  can  scarcely  be  looked  upon  as  normal  constituents  of  urine. 

Saline  Matter. — The  sulphuric  acid  in  the  urine  is  combined 
chiefly  or  entirely  with  sodium  or  potassium  ;  forming  salts  which 
are  taken  in  very  small  quantity  with  the  food,  and  are  scarcely 
found  in  other  fluids  or  tissues  of  the  body ;  for  the  sulphates 
commonly  enumerated  among  the  constituents  of  the  ashes  of  the 
tissues  and  fluids  are  for  the  most  part,  or  entirely,  produced  by 
the  changes  that  take  place  in  the  burning.  Only  about  one- 
third  of  the  sulphuric  acid  found  in  the  urine  is  derived  directly 
from  the  food  (Parkes).  Hence  the  greater  part  of  the  sulphuric 
acid  which  the  sulphates  in  the  urine  contain,  must  be  formed  in 
the  blood,  or  in  the  act  of  secretion  of  urine;  the  sulphur  of  which 
the  acid  is  formed  being  probably  derived  from  the  decomposing 


44S  THE   KIDNEYS   AND   UPJXE.  [chap.  xnr. 

nitrogenous  tissues,  the  other  elements  of  which  are  resolved  into 
urea  and  uric  acid.  It  may  be  in  part  derived  also  from  the 
sulphur-holding  taurin  and  cy.<tin.  which  can  be  found  in  the  liver, 
lungs,  and  other  parts  of  the  body,  but  not  generally  in  the 
excretions:  and  which,  therefore,  must  be  broken  up.  The  oxygen 
is  supplied  through  the  lungs,  and  the  heat  generated  dming 
combination  with  the  sulphur,  is  one  of  the  subordinate  means  by 
which  the  animal  temperature  is  maintained. 

Besides  the  sulphur  in  these  salts,  some  also  appears  to  be  in 
the  urine,  uncombined  with  oxygen  :  for  after  all  the  sulphates 
have  been  removed  from  urine,  sulphuric  acid  may  be  formed  by 
drying  and  burning  it  with  nitre.  From  three  to  five  grains  of 
sulphur  are  thus  daily  excreted.  The  combination  in  which  it 
exists  is  uncertain  :  possibly  it  is  in  some  compound  analogous  to 
cvstin  or  cystic  oxide  (p.  449).  Sulphuric  acid  also  exists 
normally  in  the  urine  in  combination  with  phenol  (C6H60;  as 
phenol  sulphuric  acid  or  its  corresponding  salts,  with  sodium,  Ac 

The  phosphoric  add  in  the  urine  is  combined  partly  with  the 
alkalies,  partly  with  the  alkaline  earths — about  four  or  five  times 
as  much  with  the  former  as  with  the  latter.  In  blood,  saliva,  and 
other  alkaline  fluids  of  the  body,  phosphates  exist  in  the  form  of 
alkaline,  neutral,  or  acid  salts.  In  the  urine  they  are  acid  salts, 
viz.,  the  sodium,  ammonium,  calcium,  and  magnesium  phosphates, 
the  excess  of  acid  being  (Liebig)  due  to  the  appropriation  of  the 
alkali  with  which  the  phosphoric  acid  in  the  blood  is  combined,  by 
the  several  new  acids  which  are  formed  or  discharged  at  the 
kidneys,  namely,  the  uric,  hippuric,  and  sulphuric  acids,  all  of 
which  are  neutralised  with  soda. 

The  phosphates  are  taken  largely  in  both  vegetable  and  animal 
food ;  some  thus  taken  are  excreted  at  once ;  others,  after  being 
transformed  and  incorporated  with  the  tissues.  Calcium  phos- 
phate forms  the  principal  earthy  constituent  of  bone,  and  from 
the  decomposition  of  the  osseous  tissue  the  urine  derives  a  large 
quantity  of  this  salt.  The  decomposition  of  other  tissues  also, 
but  especially  of  the  brain  and  nerve-substance,  furnishes  large 
supplies  of  phosphorus  to  the  urine,  which  phosphorus  is  sup- 
posed, like  the  sulphur,  to  be  united  with  oxygen,  and  then  com- 
bined with  bases.  This  quantity  is,  however,  liable  to  considerable 
variation.     Any  undue  exercise  of  the  bruin,  and  all  cii'cumstances 


chap.  rni.J  CYSTIN.  449 

producing  nervous  exhaustion,  increase  it.  The  earthy  phosphates 
are  more  abundant  after  meals,  whether  on  animal  or  vegetable 
food,  and  are  diminished  after  long  fasting.  The  alkaline  phos- 
phates are  increased  after  animal  food,  diminished  after  vegetable 
food.  Exercise  increases  the  alkaline,  but  not  the  earthy  phos- 
phates   (Bence    Jones).      Phosphorus    uncombined   with    oxygen 


Kg.  231.— Urinary  sediment  of  triple  phosphates  (large  prismatic  crystals)   and  urate  of 
ammonium,  from  urine  which  had  undergone  alkaline  fermentation. 

appears,  like  sulphur,  to  be  excreted  in  the  urine  (Ronalds). 
When  the  urine  undergoes  alkaline  fermentation,  phosphates  are 
deposited  in  the  form  of  an  urinary  sediment,  consisting  chiefly  of 
ammonio-magnesium  phosphate  (triple  phosphate)  (fig.  251). 
This  compound  does  not,  as  such,  exist  in  healthy  urine.  The 
ammonia  is  chiefly  or  wholly  derived  from  the  decomposition  of 
urea  (p.  442). 

The  chlorine  of  the  urine  occurs  chiefly  in  combination  with 
sodium,  but  slightly  also  with  ammonium,  and,  perhaps,  potassium. 
As  the  chlorides  exist  largely  in  food,  and  in  most  of  the  animal 
fluids,  their  occurrence  in  the  urine  is  easily  understood. 

Cystin  (C3H7N  S02)  (fig.  252)  is  an  occasional  constituent  of 
urine.  It  resembles  taurin  in  containing  a  large  quantity  of 
sulphur — more  than  25  per  cent.  It  does  not  exist  in  healthy 
urine. 

Another  common  morbid  constituent  of  the  urine  is  oxalic  acid, 
which  is  frequently  deposited  in  combination  with  calcium  (fig. 
253)  as  an  urinary  sediment.  Like  cystin,  but  much  more  com- 
monly, it  is  the  chief  constituent  of  certain  calculi. 

G  G 


450 


THE   KIDNEYS   AND   UKINE. 


[chap.  xiii. 


Of  the  other  abnormal  constituents  of  the  urine  mentioned  it 
will  be  unnecessary  to  speak  at  length  in  this  work. 


Tig.  252. —  Crystals  oj 


Fig.  253. — Crystals  of  calcium  oj 


Gases.— A  small  quantity  of  gas  is  naturally  present  in  the 
urine  in  a  state  of  solution.  It  consists  of  carbonic  acid  (chiefly) 
and  nitrogen  and  a  small  quantity  of  oxygen. 


The  Method  of  the  Excretion  of  Urine. 

The  excretion  of  the  urine  by  the  kidney  is  believed  to  consist 
of  two  more  or  less  distinct  processes — viz.,  (1.)  of  tilt  ration,  by 
which  the  water  and  the  ready-formed  salts  are  eliminated  ;  and, 
(2.)  of  true  secretion,  by  which  certain  substances  forming  the  chief 
and  more  important  part  of  the  urinary  solids  are  removed  from  the 
blood.  This  division  of  function  corresponds  more  or  less  to  the 
division  in  the  functions  of  other  glands  of  which  we  have  already 
treated.     It  will  be  as  well  to  consider  them  separately. 

(1.)  Of  Filtration. — This  part  of  the  renal  function  is  per- 
formed within  the  Malpighian  corpuscles  by  the  renal  glomeruli. 
By  it  not  only  the  water  is  strained  off,  but  also  certain  other 
constituents  of  the  urine,  e.g.,  sodium  chloride,  are  separated. 
The  amount  of  the  fluid  filtered  off  depends  almost  entirely  upon 
the  blood-pressure  in  the  glomeruli. 

The  greater  the  blood-pressure  in  the  arterial  system  generally, 
and  consequently  in  the  renal  arteries,  the  greater,  cateris  paribus, 
will  be  the  blood-pressure  in  the  glomeruli,  and  the  greater  the 


CHAP,  xiii.]  KXCRETloX    OF    CHINK. 


15' 


quantity  of  urine  separated;  but  even  without  increase  of  the  general 
blood-pressure,  if  the  renal  arteries  be  locally  dilal 

in  the  glomeruli  will  lie  increased  and  with  itth-  tion  of  urine. 

<>n  the  other  hand,  if  the  local  blood-pressure  be  diminished,  the 
amount  of  fluid  will  be  Lessen*  d.  All  the  numepous  causes,  there- 
tore,  which   increase  the    blood-pressure  (p.  189)  will,  us   a  rule, 

ndarily  increase  the  secretion  of  urine.  Of  these  the  hi 
a. -tion  is  amongst  the  most  important.  When  its  contractions  are 
increased  in  force,  incr<  ised  diuresis  is  the  result.  Similarly, 
causes  which  lower  the  blood-pressure,  •.</.,  enfeebled  action  of  the 
heart,  great  loss  of  blood,  &c,  will  diminish  the  activity  of  the 
vtion  of  urine. 
The  close  connection  between  the  blood-pressure  generally  and 
the  nervous  system  has  been  before  considered,  and  it  will  be 
clear,  therefore,  that  the  amount  of  urine  secreted  depends  greatly 
upon  the  influence  of  the  nervous  system.  Thus,  division  of 
the  spinal  cord,  by  producing  general  vascular  dilatation,  causes  a 
great  diminution  of  blood-pressure,  and  so  diminishes  the  amount 
of  water  passed  ;  since  the  local  dilatation  in  the  renal  arteries 
is  not  sufficient  to  counteract  the  general  diminution  of  pressure. 
Stimulation  of  the  cut  cord  produces,  strangely  enough,  the 
same    results — i.e.,    a    diminution    in   the    amount  of   the  urine 

d,  but  in  a  different  way,  viz.,  by  constricting  the  arteries 
generally,  ami,  among  others,  the  renal  arteries  ;  the  diminution 
of  blood-pressure  resulting  from  the  local  resistance  in  the  renal 
arteries  being  more  potent  to  diminish  blood-pressure  in  the 
glomeruli  than  the  general  increase  of  blood-pressure  is  to  increase 
it.  Section  of  the  renal  nerves  or  of  any  others  which  produce 
local  dilatation  without  greatly  diminishing  the  general  blood- 
pressure  will  cause  an  increase  in  the  quantity  of  fluid  passed. 

The  fact  that  in  summer  or  in  hot  weather  the  urine  is 
diminished  may  be  attributed  partly  to  the  copious  elimination 
of  water  by  the  skin  in  the  form  of  sweat  which  occurs  in 
summer,  as  contrasted  with  the  greatly  diminished  functional 
activity  of  the  skin  in  winter,  but  also  to  the  dilated  condition  of 
the  vessels  of  the  skin  causing  a  decrease  in  the  general  blood- 

ure.  Thus  we  see  that  in  regard  to  the  elimination  of  water 
from  the  system,  the  skin  and  kidneys  perform  similar  functions, 
and  are  capable  to  some  extent  of  acting  vicariously,  one  for  the 

G  q  2 


452  THE   KIDNEYS   AND   URINE.  [chap.  xiii. 

other.     Their  relative  activities  are  inversely  proportional  to  each 
other. 

The  intimate  connection  between  the  condition  of  the  kidney 
and  the  blood-pressure  has  been  exceedingly  well  shown  by  the 
introduction  of  an  instrument  called  the  Oncometer,  recently  in- 
troduced by  Roy,  which  is  a  modification  of  the  plethy sinograph 
(fig.    138).      By  means  of  this  apparatus   any   alteration  in  the 
volume   of  the  kidney  is   communicated  to  an  apparatus  (onco- 
graph) capable  of  recording  graphically,  with  a  writing  lever,  such 
variations.     It  has  been  found  that  the  kidney  is  extremely  sensi- 
tive to  any  alteration  in  the  general  blood-pressure,  every  fall  in 
the  general  blood-pressure  being  accompanied  by  a  decrease  in  the 
volume  of  the  kidney,  and  every  rise,  unless  produced  by  consider- 
able constriction  of  the  peripheral  vessels,  including  those  of  the 
kidney,  being  accompanied  by  a  corresponding  increase  of  volume. 
Increase  of  volume   is  followed  by  an  increase   in  the  amount  of 
urine  secreted,  and  decrease  of  volume  by  a  decrease  in  the  secre- 
tion.    In    addition,  however,  to  the   response   of  the  kidney  to 
alterations    in  the  general    blood-pressure,    it    has   been    further 
observed  that  certain  substances,  when  injected  into  the  blood, 
will   also    produce    an    increase    in  volume    of   the    kidney,   and 
consequent  increased  flow  of  urine,  without  affecting  the  general 
blood-pressure — such  bodies  as  sodium  acetate  and  other  diuretics. 
These  observations  appear  to  prove  that  local  dilatation  of  the 
renal  vessels  may  be  produced  by  alterations  in  the  blood  upon  a 
local  nervous  mechanism,  as  the  effect  is  produced  when  all  of 
the  renal    nerves  have   been    divided.     The   alterations  are  not 
only  produced  by  the  addition  of  drugs,  but   also   by  the  intro- 
duction   of   comparatively    small    quantities  of   water    or    saline 
solution.     To  this  alteration  of  the  blood  acting  upon  the  renal 
vessels  (either  directly  or)  through  a  local  vaso-motor  mechanism, 
and  not  to    any  great  alteration  in  the  general  blood-pressure, 
must  we  attribute  the  effect  of  meals,  &c.s  observed  by  Roberts. 
''  The  renal   excretion   is  increased  after   meals   and   diminished 
during  fasting  and  sleep.      The   increase    began   within    the   first 
hour  after  breakfast,  and  continued  during  the  succeeding  two  or 
three  hours  :  then  a  diminution  set  in,   and  continued  until    an 
hour  or  two  after  dinner.     The  effect  of  dinner  did  not  appear 
until  two   or  three   hours    after    the    meal ;  and  it   reached  its 


cii.u'.  xm.]  EXCBETIOfl   OF   URINE.  453 

maximum  about  the  fourth  hour.  Prom  this  period  the  excretion 
steadily  decreased  until  bed-time.  During  sleep  ft  sank  still  lower, 
ami  reached  its  minimum- — being  not  more  than  one-third  of  the 
quantity  excreted  during  the  hours  of  digestion."  The  increased 
amount  of  urine  passed  after  drinking  large  quantities  of  fluid 
probably  depends  upon  the  diluted  condition  of  the  blood  thereby 
induced. 

The  following  table*  will  help  to  explain  the  dependence  of  the 
filtration  function  upon  the  blood-pressure  and  the  nervous 
system  : — 

TABLE    OF    THE    RELATION    OF    THE     SECRETION    OF    URINE 
TO    ARTERIAL    PRESSURE. 

A.  Secretion  of  urine  may  be  increased— 

a.  Jiy  increasing  the  general  blood-pressure,  by 

1.  Increase  of  force  or  frequency  of  heart-beat. 

2.  Constriction  of  small  arteries  of  areas  other  than  the  kidney. 

b.  Jitj  relaxation  of  the  renal  artery  without  compensating  relaxa- 

tion elsewJiere,  by 

1.  Division  of  the  renal  nerves  (causing  polyuria). 

2.  .,  „  ,,       and  afterwards  stimulating  cord 
below  medulla  (causing  greater  polyuria). 

3.  Division  of  the  splanchnic  nerves  ;  but  polyuria  is  less  than 

in  1  or  2.  as  these  nerves  are  distributed  to  a  wider  area 
the  dilatation  of  the  renal  artery  is  accompanied  by 
dilatation  of  other  vessels,  and  therefore  with  a  some- 
what diminished  general  blood  supply. 

4.  Puncture  of  the  floor  of  fourth  ventricle  or  mechanical  irri- 

tation of  the  superior  cervical  ganglion  of  the  sympa- 
thetic, possibly  from  dilatation  of  the  renal  arteries. 

B.  Secretion  of  urine  may  be  diminished— 

a.  Jiy  diminishing  the  general  blood-pressure,  by 

1.  Diminishing  the  force  or  frequency  of  the  heart-beats. 

2.  Dilatation  of  capillary  areas  other  than  the  kidney. 

3.  Division  of  spinal  cord  below  medulla,  which  causes  dilata- 

tion of  general  abdominal  area,  and  urine  generally 
ceases  being  secreted. 

b.  By  increasing  the  blood-pressure,  by  stimulation  of  spinal  cord 

below  medulla,  the  constriction  of  the  renal  artery  not  being 
compensated  for  by  the  increase  of  general  blood-pressure. 

c.  By  constriction   of  the   renal  artery,  by  stimulating  the  renal  or 

splanchnic  nerves,  or  by  stimulating  the  spinal  cord. 


*  Modified  from  M.  Foster. 


454  THE   KIDXEYS   AND   UEINE.  chap.  xiii. 

Although  it  is  convenient  to  call  the  processes  which  go  on  in 
the  renal  glomeruli,  filtration,  there  is  reason  to  believe  that  they 
are  not  absolutely  mechanical,  as  the  term  might  seem  to  imply, 
since,  when  the  epithelium  of  the  Malpighian  capsule  has  been, 
as  it  were,  put  out  of  order  by  ligature  of  the  renal  artery,  on 
removal  of  the  ligature,  the  urine  has  been  found  temporarily 
to  contain  albumen,  indicating  that  a  selective  power  resides  in 
the  healthy  epithelium,  which  allows  a  certain  constituent  part  of 
the  blood  to  be  filtered  off  and  not  others. 

(2.)  Of  True  Secretion. — That  there  is  a  second  part  in  the 
process  of  the  excretion  of  urine,  which  is  true  secretion,  is 
suggested  by  the  structure  of  the  tubuli  uriniferi,  and  the  idea  is 
supported  by  various  experiments.  It  will  be  remembered  that 
the  convoluted  portions  of  the  tubules  are  lined  with  epithelium, 
which  bears  a  close  resemblance  to  the  secretory  epithelium  of 
other  glands,  whereas  the  Malpighian  capsules  and  portions  of 
the  loops  of  Henle  are  lined  simply  by  endothelium.  The  two 
functions  are,  then,  suggested  by  the  differences  of  epithelium, 
and  also  by  the  fact  that  the  blood  supply  is  different,  since  the 
convoluted  tubes  are  surrounded  by  capillary  vessels  derived 
from  the  breaking  up  of  the  efferent  vessels  of  the  Malpighian 
tufts.  The  theory  first  suggested  by  Bowman  (1842),  and  still 
generally  accepted,  of  the  function  of  the  two  parts  of  the 
tubules,  is  that  the  cells  of  the  convoluted  tubes,  by  a  process 
of  true  secretion,  separate  from  the  blood  substances  such  as 
urea,  whereas  from  the  glomeruli  are  separated  the  water  and  the 
inorganic  salts.  Another  theory  suggested  by  Ludwig  (1844)  is 
that  in  the  glomeruli  is  filtered  off  from  the  blood  all  the  con- 
stituents of  the  urine  in  a  very  diluted  condition.  When  this 
passes  along  the  tortuous  uriniferous  tube,  part  of  the  water  is 
re-absorbed  into  the  vessels  surrounding  them,  leaving  the  urine 
in  a  more  concentrated  condition — retaining  all  its  proper  con- 
stituents. This  osmosis  is  promoted  b}-  the  high  specific  gravity 
of  the  blood  in  the  capillaries  surrounding  the  convoluted  tubes, 
but  the  return  of  the  urea  and  similar  substances  is  prevented 
by  the  secretory  epithelium  of  the  tubules.  Ludwig's  theory, 
however  plausible,  must,  we  think,  give  way  to  the  first  theory, 
which  is  more  strongly  supported  by  direct  experiment. 

By  using  the  kidney  of  the  newt,  which  has  two  distinct  vas- 


ohap.  sin.]  EXCRETION   OF    I'lMXK.  455 

nihil-  supplies,  one  from  the  renal  artery  to  the  glomeruli,  and  the 
other  from  the  renal  portal  vein  to  the  convoluted  tubes,  Nus 
baum  has  shown  that  certain  Bubstances,  <-.//.,  peptones,  sugar, 
when  injected  into  the  blood,  are  eliminated  by  the  glomeruli,  and 
bo  arc  not  got  rid  of  when  the  renal  arteries  are  tied;  whereas 
certain  other  substances,  e.g.,  urea,  when  injected  into  the  blood. 
;.rj  eliminated  by  the  convoluted  tubes,  even  when  the  renal 
arteries  have  been  tied.  This  evidence  is  very  direct  that  urea 
is  excreted  by  the  convoluted  tubes. 

Heidenhain  also  has  shown  by  experiment  that  if  a  substance 
(sodium  sulphindigotate),  which  ordinarily  produces  bine  urine, 
be  injected  into  the  blood  after  section  of  the  medulla  which 
causes  lowering  of  the  blood-pressure  in  the  renal  glomeruli,  that 
when  the  kidney  is  examined,  the  cells  of  the  convoluted  tubules 
(and  of  these  alone)  are  stained  with  the  substance,  which  is  also 
found  in  the  lumen  of  the  tubules.  This  appears  to  show  that 
under  ordinary  circumstances  the  pigment  at  any  rate  is  elimi- 
nated by  the  cells  of  the  convoluted  tubules,  and  that  when  by 
diminishing  the  blood-pressure,  the  filtration  of  urine  ceases,  the 
pigment  remains  in  the  convoluted  tubes,  and  is  not,  as  it  is  under 
ordinary  circumstances,  swept  away  from  them  by  the  flushing 
of  them  which  ordinarily  takes  place  with  the  watery  part  of 
urine  derived  from  the  glomeruli.  It  therefore  is  probable  that 
the  cells,  if  they  excrete  the  pigment,  excrete  urea  and  other 
substances  also.  But  urea  acts  somewhat  differently  to  the  pig- 
ment, as  when  it  is  injected  into  the  blood  of  an  animal  in  which 
the  medulla  has  been  divided  and  the  secretion  of  urine  stopped, 
a  copious  secretion  of  urine  results,  which  is  not  the  case  when 
the  pigment  is  used  instead  under  similar  conditions.  The  flow 
of  urine,  independent  of  the  general  blood-pressure,  might  be 
supposed  to  be  due  to  the  action  of  the  altered  blood  upon  some 
local  vaso-motor  mechanism ;  and,  indeed,  the  local  blood- 
pressure  is  directly  affected  in  this  way,  but  there  is  reason  for 
believing  that  part  of  the  increase  of  the  secretion  is  due  to 
the  direct  stimulation  of  the  cells  by  the  urea  contained  in  the 
blood. 

To  sum  up,  then,  the  relation  of  the  two  functions  :  (1.)  The 
process  of  filtration,  by  which  the  chief  part  if  not  the  whole  of 
the  fluid    is    eliminated,    together  with   certain  inorganic   salts* 


456  THE   KIDNEYS   AND   UPJXE.  [chap.  xiii. 

and  possibly  other  solids,  is  directly  dependent  upon  blood- 
pressure,  is  accomplished  by  the  renal  glomeruli,  and  is  accom- 
panied by  a  free  discharge  of  solids  from  the  tubules.  (2.)  The 
process  of  secretion  proper,  by  which  urea  and  the  principal 
urinary  solids  are  eliminated,  is  only  indirectly,  if  at  all,  depen- 
dent upon  blood-pressure  and  is  accomplished  by  the  cells  of  the 
convoluted  tubes.  It  is  sometimes  accompanied  by  the  elimination 
of  copious  fluid,  produced  by  the  chemical  stimulation  of  the 
epithelium  of  the  same  tubules. 


Sources  of  the  Nitrogenous  Urinary  Solids. 

Urea. — In  speaking  of  the  method  of  the  secretion  of  urine, 
it  was  assumed  that  the  part  played  by  the  cells  of  the  uriniferous 
tubules  was  that  of  mere  separation  of  the  constituents  of  the 
urine  which  existed  ready-formed  in  the  blood  :  there  is  consider- 
able evidence  to  favour  this  assumption.  What  may  be  called 
the  specially  characteristic  solid  of  the  urine,  i.e.,  urea  (as  well  as 
most  of  the  other  solids),  may  be  detected  in  the  blood,  and  in 
other  parts  of  the  body,  e.g.,  the  humours  of  the  eye  (Millon),  even 
while  the  functions  of  the  kidneys  are  unimpaired  :  but  when 
from  any  cause,  especially  extensive  disease  or  extirpation  of  the 
kidneys,  the  separation  of  urine  is  imperfect,  the  urea  is  found 
largely  in  the  blood  and  in  most  other  fluids  of  the  body. 

It  must,  therefore,  be  clear  that  the  urea  is  for  the  most  part 
made  somewhere  else  than  in  the  kidneys,  and  simply  brought  to 
them  by  the  blood  for  elimination.  It  is  not  absolutely  proved, 
however,  that  all  the  urea  is  formed  away  from  these  organs,  and 
it  is  possible  that  a  small  quantity  is  actually  secreted  by  the  cells 
of  the  tubules.  The  sources  of  the  urea,  which  is  brought  to  the 
kidneys  for  excretion,  are  stated  to  be  two. 

(1.)  From  the  splitting  vp  the  Elements  of  the  Nitrogenous  Food. — 
The  origin  of  urea  from  this  source  is  shown  by  the  increase 
which  ensues  on  substituting  an  animal  or  highly  nitrogenous 
for  a  vegetable  diet ;  in  the  much  larger  amount — nearly  double 
— excreted  by  Carnivora  than  Herbivora,  independent  of  exercise  ; 
and  in  its  diminution  to  about  one-half  during  starvation,  or 
during  the  exclusion  of  non-nitrogenous  principles  of  food.  Part, 
at  any  rate,  of  the  increased  amount  of  urea  which  appears  in  the 


chap,  kiii.]  S0UBCE8  OF   ri;i:.\.  457 

urine  bood  after  a  full  meal  bfproteid  material  may  be  attributed 
to  the  production  of  a  considerable  amount  of  leucin  andtyrosin  as 
by-products  of  pancreatic  digestion.  These  Bubstances  are  carried 
by  the  portal  vein  to  the  liver,  and  it  is  there  that  the  change 
in  all  probability  takes  place  :  as  when  the  functions  of  the  organ 
are  gravely  interfered  with,  as  in  the  ease  of  acute  yellow  atrophy, 
the  amount  of  urea  is  distinctly  diminished,  and  its  place  appears 
t<>  be  taken  by  leucin  and  tyrosin.  It  has  been  found  by  experi- 
ment, too,  that  if  these  siihstanees  he  introduced  into  the  alimen- 
tary canal,  the  introduction  is  followed  by  a  corresponding  increase 
in  the  amount  of  urea,  but  not  by  the  presence  of  the  bodies 
themselves  in  the  urine. 

(2.)  From  the  nitrogenous  metabolism  of  the  tissues.-^-Thm  second 
origin  of  urea  is  shown  by  the  fact  that  it  continues  to  be  ex- 
creted, though  in  smaller  quantity  than  usual,  when  all  nitroge- 
nous substances  are  strictly  excluded  from  the  food,  as  when  the 
diet  consists  for  several  days  of  sugar,  starch,  gum,  oil,  and  similar 
non-nitrogenous  substances  (Lehmann).  It  is  excreted  also,  even 
though  no  food  at  all  be  taken  for  a  considerable  time;  thus  it 
is  found  in  the  urine  of  reptiles  which  have  fasted  for  months  ; 
and  in  the  urine  of  a  madman,  who  had  fasted  eighteen  days, 
Lassaigne  found  both  urea  and  all  the  components  of  healthy 
urine. 

Turning  to  the  muscles,  however,  as  the  most  actively  meta- 
bolic tissue,  we  find  as  a  result  of  their  activity  not  urea,  but 
kreatin  ;  and  although  it  may  be  supposed  that  some  of  this  latter 
body  appears  naturally  in  the  urine  as  kreatinin,  yet  it  is  not  in 
sufficient  quantity  to  represent  the  large  amount  of  it  formed  by 
the  muscles,  and,  indeed,  by  others  of  the  tissues.  It  is  assumed 
that  kreatin  therefore  is  the  nitrogenous  antecedent  of  urea; 
where  its  conversion  into  urea  takes  place  is  doubtful,  but  very 
likely  the  liver,  and  possibly  the  spleen,  may  be  the  seats  of  the 
change.  It  may  be,  however,  that  part — but  if  so,  a  small  part 
— reaches  the  kidneys  without  previous  change,  leaving  it  to  the 
cells  of  the  renal  tubules  to  complete  the  action.  In  speaking 
of  kreatin  as  the  antecedent  of  urea,  it  should  be  recollected  that 
other  nitrogenous  products,  such  as  xanthin  (C5  H4  N4  02),  appear 
in  conjunction  with  it,  and  that  these  may  also  be  converted  into 
urea. 


4-§  THE  KIDNEYS   AND   URINE.  [chap.  xni. 

It  was  formerly  taken  for  granted  that  the  quantity  of 
urea  in  the  urine  is  greatly  increased  by  active  exercise  ;  but 
numerous  observers  have  failed  to  detect  more  than  a  slight 
increase  under  such  circumstances  ;  and  our  notions  concerning 
the  relation  of  this  excretory  product  to  the  destruction  of 
muscular  fibre,  consequent  on  the  exercise  of  the  latter,  have 
undergone  considerable  modification.  There  is  no  doubt,  of 
course,  that  like  all  parts  of  the  body,  the  muscles  have  but  a 
limited  term  of  existence,  and  are  being  constantly  although  very 
slowly  renewed,  at  the  same  time  that  a  part  of  the  products  of 
their  disintegration  appears  in  the  urine  in  the  form  of  urea.  But 
the  waste  is  not  so  fast  as  it  was  formerly  supposed  to  be  ;  and 
the  theory  that  the  amount  of  work  done  by  the  muscle  is  ex- 
pressed by  the  quantity  of  urea  excreted  in  the  urine  must  without 
doubt  be  given  up. 

Uric  Acid. — Uric  acid  probably  arises  much  in  the  same  way 
as  urea,  either  from  the  disintegration  of  albuminous  tissues,  or 
from  the  food.  The  relation  which  uric  acid  and  urea  bear  to 
each  other  is,  however,  still  obscure  :  but  uric  acid  is  said  to  be  a 
less  advanced  stage  of  the  oxidation  of  the  products  of  proteid 
metabolism.  The  fact  that  they  often  exist  together  in  the  same 
mine,  makes  it  seem  probable  that  they  have  different  origins  ; 
but  the  entire  replacement  of  either  by  the  other,  as  of  urea  by 
uric  acid  in  the  urine  of  birds,  serpents,  and  many  insects,  and  of 
uric  acid  by  urea,  in  the  urine  of  the  feline  tribe  of  Mammalia, 
shows  that  either  alone  may  take  the  place  of  the  two.  At  any 
rate,  although  it  is  true  that  one  molecule  of  uric  acid  is  capable 
of  splitting  up  into  two  molecules  of  urea  and  one  of  mes-oxalic 
acid,  there  is  no  evidence  for  believing  that  uric  acid  is  an  ante- 
cedent of  urea  in  the  nitrogenous  metabolism  of  the  body. 
Some  experiments  seem  to   show  that  uric  acid  is  formed  in  the 

kidney. 

Hippuric  Acid  (C9H9N0s) — Hippuric  acid  is  closely  allied  to 
benzoic  acid :  and  this  substance  when  introduced  into  the  system,  is 
excreted  by  the  kidneys  as  hippuric  acid  (Ure).  Its  source  is  not 
satisfactorily  determined  :  in  part  it  is  probably  derived  from  some 
constituents  of  vegetable  diet,  though  man  has  no  hippuric  acid 
in  his  food,  nor,  commonly,  any  benzoic  acid  that  might  be  con- 
verted into  it ;  in  part  from  the  natural  disintegration  of  tissues, 


ohap.  xiii.]  EXCRETION   OF   (TRINE,  acq 

independent  of  vegetable  food,  for  Weismann  constantly  found 
an  appreciable  quantity,  even  when  living  on  an  exclusively 
animal  diet.  Bippuric  acid  arises  from  the  union  of  benzoic  acid 
with  glycin  (C,H5N0,+CrHa0,=C9H9N0,+H,0),  which 
union  may  take  place  in  the  kidneys  themselves,  as  well  as  in  the 
liver. 

Extractives. — The  source  of  the  extractives  of  the  urine  is 
probably  in  chief  part  the  disintegration  of  the  nitrogenous  tissues, 
but  we  are  unable  to  say  whether  these  nitrogenous  bodies 
are  merely  accidental,  having  resisted  further  decomposition 
into  urea,  or  whether  they  are  the  representatives  of  the  decom- 
position of  special  tissues,  or  of  special  forms  of  metabolism  of  the 
tissues.  There  is,  however,  one  exception,  and  this  is  in  the  case 
of  kreatinin  ;  there  is  great  reason  for  believing  that  the  amount 
of  this  body  which  appears  in  the  urine  is  derived  from  the  meta- 
bolism of  the  nitrogenous  food,  as  when  this  is  diminished,  it 
diminishes,  and  when  stopped,  it  no  longer  appears  in  the  urine. 

The  Passage  of  Urine  into  the  Bladder. 

As  each  portion  of  ivrine  is  secreted  it, propels  that  which  is. 
already  in  the  tubes  onwards  into  the  pelvis  of  the  kidney. 
Thence  through  the  ureter  the  urine  passes  into  the  bladder,  into 
which  its  rate  and  mode  of  entrance  has  been  watched  in  cases  of 
ectopia  vesiae,  i.e.,  of  such  fissures  in  the  anterior  or  lower  part  of 
the  walls  of  the  abdomen,  and  of  the  front  wall  of  the  bladder,  as 
expose  to  view  its  hinder  wall  together  with  the  orifices  of  the 
ureters.  The  urine  does  not  enter  the  bladder  at  any  regular  rate, 
nor  is  there  a  synchronism  in  its  movement  through  the  two 
ureters.  During  fasting,  two  or  three  drops  enter  the  bladder 
every  minute,  each  drop  as  it  enters  first  raising  up  the  little 
papilla  on  which,  in  these  cases  the  ureter  opens,  and  then  passing 
slowly  through  its  orifice,  which  at  once  again  closes  like  a 
sphincter.  In  the  recumbent  posture,  the  urine  collects  for  a  little 
time  in  the  ureters,  then  flows  gently,  and,  if  the  body  be  raised, 
runs  from  them  in  a  stream  till  they  are  empty.  Its  flow  is 
increased  in  deep  inspiration,  or  straining,  and  in  active  exercise, 
and  in  fifteen  or  twenty  minutes  after  a  meal  (Erichsen).  The 
urine  collecting  is  prevented  from  regurgitation  into  the  ureters  by 


460  THE   KIDNEYS   AND    URINE,  [chap.  xiii. 

the  mode  in  which  these  pass  through  the  walls  of  the  bladder, 
namely,  by  their  lying  for  between  half  and  three-quarters  of  an 
inch  between  the  muscular  and  mucous  coats  before  they  turn 
rather  abruptly  forwards,  and  open  through  the  latter  into  the 
interior  of  the  bladder. 

Micturition. — The  contraction  of  the  muscular  walls  of  the 
bladder  may  by  itself  expel  the  urine  with  little  or  no  help  from 
other  muscles,  when  the  sphincter  of  the  organ  is  relaxed.  In  so 
far,  however,  as  it  is  a  voluntary  act,  micturition  is  performed 
by  means  of  the  abdominal  and  other  expiratory  muscles  which, 
in  their  contraction,  press  on  the  abdominal  viscera,  the  diaphragm 
being  fixed,  and  cause  the  expulsion  of  the  contents  of  the  bladder. 
The  muscular  coat  of  the  bladder  co-operates,  in  micturition,  by 
reflex  involuntary  action,  with  the  abdominal  muscles ;  and  the 
act  is  completed  by  the  accelerator  urince,  which,  as  its  name 
implies,  quickens  the  stream,  and  expels  the  last  drops  of 
urine  from  the  urethra.  The  act,  so  far  as  it  is  not  directed  by 
volition,  is  under  the  control  of  a  nervous  centre  in  the  lumbar 
spinal  cord,  through  which,  as  in  the  case  of  the  similar  centre 
for  defalcation  (p.  357),  the  various  muscles  concerned  are 
harmonized  in  their  action.  It  is  well  known  that  the  act  may 
be  reflexly  induced,  e.g.,  in  children  who  suffer  from  intestinal 
worms,  or  other  such  irritation.  Generally  the  afferent  impulse 
which  calls  into  action  the  desire  to  micturate  is  excited  by  over 
distention  of  the  bladder,  or  even  by  a  few  drops  of  urine  passing 
into  the  urethra. 


ohap.  xiv.]  l  UK   VASCULAB   GLAND&  461 


('HALTER    XIV. 

THE  VASCTJLAB   GLANDS. 

'I'm:  materials  separated  from  the  blood  by  the  ordinary 
process  of  Becretion  in  glands,  are  always  discharged  from  the 
organ  in  which  they  are  formed,  and  are  either  straightway  expelled 
from  the  body,  or  if  they  are  again  received  into  the  Mood,  it  is 
only  after  they  have  been  altered  from  their  original  condition, 
as  in  the  cases  of  the  saliva  and  bile.  There  appears,  however, 
to  be  a  modification  of  the  process  of  secretion,  in  which  certain 
materials  are  abstracted  from  the  blood,  undergo  some  change, 
and  are  added  t<»  the  lymph  or  restored  to  the  blood,  without 
being  previously  discharged  from  the  secreting  organ,  or  made 
of  for  any  secondary  purpose.  The  bodies  in  which  this 
modified  form  of  secretion  takes  place,  are  usually  described  as 
vascular  glands,  or  glands  without  ducts,  and  include  the  spleen,  the 
thymus  and  thyroid  glands,  the  suprarenal  capsules,  the  pineal  gland 
and  pituitary  body,  the  tonsil*.  The  solitary  and  agminate  glands 
(Peyer's)  of  the  intestine,  and  lymph-glands  in  general,  also 
closely  resemble  them;  indeed,  both  in  structure  and  function, 
the  vascular  glands  bear  a  close  relation,  on  the  one  hand,  to  the 
true  secreting  glands,  and  on  the  other,  to  the  lymphatic  glands. 
The  evidence  in  favour  of  the  view  that  these  organs  exercise 
a  function  analogous  to  that  of  secreting  glands,  has  been  chiefly 
obtained  from  investigations  into  their  structure,  which  have 
shown  that  most  of  the  glands  without  duets  contain  the  same 
essential  structures  as  the  secreting  glands,  except  the  ducts. 

The  Spleen. 

» 

The  Spleen  is  the  largest  of  the  so-called  ductless  glands  ;  it  is 
situated  to  the  left  of  the  stomach,  between  it  and  the  diaphragm. 
It  is  of  a  deep  red  colour,  of  a  variable  shape,  generally  oval, 
somewhat  concavo-convex.  Vessels  enter  and  leave  the  spleen  at 
the  inner  side  (hilus). 

Structure. — The   spleen    is    covered    externally  almost   com- 


462 


THE  VASCULAR  GLANDS. 


[CHAP.  XIV. 


pletely  by  a  serous  coat  derived  from  the  peritoneum,  while 
within  this  is  the  proper  fibrous  coat  or  capsule  of  the  organ. 
The  latter,  composed  of  connective  tissue,  with  a  large  prepon- 
derance of  elastic  fibres,  and   a  certain  proportion  of  unstriated 


Fig  254. — Section  of  dog's  spleen  injected:  c,  capsule ;  tr,  trabecular;  m,  two  Malpighian 
bodies  with  numerous  small  arteries  and  capillaries  ;  a,  artery  ;  /,  lymphoid  tissue. 
consisting  of  closely-packed  lymphoid  cells  supported  by  very  delicate  retif'orm  tissue  ; 
a  light  space  unoccupied  by  cells  is  seen  all  round  the  trabecular,  which  corresponds  to 
the  "  lymph  path  "  lymphatic  glands  (Schofield). 


muscular  tissue,  forms  the  immediate  investment  of  the  spleen. 
Prolonged  from  its  inner  surface  are  fibrous  processes  or  trabe- 
mlce,  containing  much  unstriated  muscle,  which  enter  the  interior 
of  the  organ,  and,  dividing  and  anastomosing  in  all  parts,  form  a 
kind  of  supporting  frame-work  or  stroma,  in  the  interstices  of 
which  the  proper  substance  of  the  spleen  {spleen-pulp)  is  contained 
(fig.  254).  At  the  hilus  of  the  spleen,  the  blood-vessels,  nerves, 
and  lymphatics  enter,  and  the  fibrous  coat  is  prolonged  into  the 


ohap.  xiv.  |  THE   SPLEEN.  463 

spleen  substance  in  the  form  of  investing  sheaths  for  the  arteries 
and  veins,  which  shcit lis  again  are  continuous  with  the  trabecula 
before  referred  to. 

The  spleen-pulp,  which  is  a  dark  red  or  reddish-brown  colour, 
is  composed  chiefly  of  cells,  imbedded  in  a  matrix  of  fibres  formed 
of  the  branchings  of  large  flattened  aucleated  endotheloid  cells. 
The  spaces  of  the  network  only  partially  occupied  by  cells  form 
a  freely  communicating  system.  Of  the  cells  some  are  granular 
corpuscles  resembling  the  lymph-corpuscles,  more  or  less  connected 
with  the  cells  of  the  meshwork,  both  in  general  appearance  and 
in  being  able  to  perform  amoeboid  movements;  others  are  red 
blood-corpuscles  of  normal  appearance  or  variously  changed  ; 
while  there  are  also  large  cells  containing  either  a  pigment  allied 
to  the  colouring  matter  of  the  blood,  or  rounded  corpuscles  like 
red  blood-cells. 

The  splenic  artery,  after  entering  the  spleen  by  its  concave 
surface,  divides  and  subdivides,  with  but  little  anastomosis 
between  its  branches  ;  at  the  same  time  its  branches  are  sheathed 
by  the  prolongations  of  fibrous  coat,  which  they,  so  to  speak, 
carry  into  the  spleen  with  them.  The  arteries  send  off  branches 
into  the  spleen-pulp  which  end  in  capillaries,  and  these  either 
communicate,  as  in  other  parts  of  the  body,  with  the  radicles  of 
the  veins,  or  end  in  lacunar  spaces  in  the  spleen-pulp,  from  which 
veins  arise  (Gray). 

The  walls  of  the  smaller  veins  are  more  or  less  incomplete,  and 
readily  allow  lymphoid  corpuscles  to  be  swept  into  the  blood- 
current.  "The  blood  traverses  the  network  of  the  pulp,  and 
interstices  of  the  lymphoid  cells  contained  in  the  latter,  in  the 
same  maimer  as  the  water  of  a  river  finds  its  way  among  the 
pebbles  of  its  bed  :  the  blood  from  the  arterial  capillaries  is 
emptied  into  a  system  of  intermediate  passages,  which  are  directly 
bounded  by  the  cells  and  fibres  of  the  network  of  the  pulp,  and 
from  which  the  smallest  venous  radicles  with  their  cribriform  walls 
take  origin  "  (Frey).  The  veins  are  large  and  very  distensible  : 
the  whole  tissue  of  the  spleen  is  highly  vascular,  and  becomes 
readily  engorged  with  blood  :  the  amount  of  distension  is,  how- 
ever, limited  by  the  fibrous  and  muscular  tissue  of  its  capsule  and 
trabecular,  which  forms  an  investment  and  support  for  the  pulpy 
mass  within. 


464  THE   VASCULAR   GLANDS.  [chap.  xiv. 

On  the  face  of  a  section  of  the  spleen  can  be  usually  seen 
readily  with  the  naked  eye,  minute,  scattered  rounded  or  oval 
whitish  spots,  mostly  from  ■—  to  -^  inch  in  diameter.  These  are 
the  Malpighian  corpuscles  of  the  spleen,  and  are  situated  on  the 
sheaths  of  the  minute  splenic  arteries,  of  which,  indeed,  they  may 
be  said  to  be  outgrowths  (fig.  254).  For  while  the  sheaths  of 
the  larger  arteries  are  constructed  of  ordinary  connective  tissue, 
this  has  become  modified  where  it  forms  an  investment  for  the 
smaller  vessels,  so  as  to  be  composed  of  adenoid  tissue,  with 
abundance  of  corpuscles,  like  lymph-corpuscles,  contained  in  its 
meshes,  and  the  Malpighian  corpuscles  are  but  small  outgrowths 
of  this  cytogenous  or  cell-bearing  connective  tissue.  They  are 
composed  of  cylindrical  masses  of  corpuscles,  intersected  in  all 
parts  by  a  delicate  fibrillar  tissue,  which  though  it  invests  the 
Malpighian  bodies,  does  not  form  a  complete  capsule.  Blood- 
capillaries  traverse  the  Malpighian  corpuscles  and  form  a  plexus 
in  their  interior.  The  structure  of  a  Malpighian  corpuscle  of  the 
spleen  is,  therefore,  very  similar  to  that  of  lymphatic -gland 
substance. 

Functions.— With  respect  to  the  office  of  the  spleen,  we  have 
the  following  data.  (1.)  The  large  size  which  it  gradually 
acquires  towards  the  termination  of  the  digestive  process,  and  the 
great  increase  observed  about  this  period  in  the  amount  of  the 
finely-granular  albuminous  plasma  within  its  parenchyma,  and 
the  subsequent  gradual  decrease  of  this  material,  seem  to  indicate 
that  this  organ  is  concerned  in  elaborating  the  albuminous  mate- 
rials of  food,  and  for  a  time  storing  them  up,  to  be  gradually 
introduced  into  the  blood,  according  to  the  demands  of  the  general 
system. 

(2.)  It  seems  probable  that  the  spleen,  like  the  lymphatic 
glands,  is  engaged  in  the  formation  of  blood-corpuscles.  For  it  is 
quite  certain,  that  the  blood  of  the  splenic  vein  contains  an 
unusually  large  amount  of  white  corpuscles ;  and  in  the  disease 
termed  leucocythamria,  in  which  the  pale  corpuscles  of  the  blood 
are  remarkably  increased  in  number,  there  is  almost  always  found 
an  hypertrophied  state  of  the  spleen  or  of  the  lymphatic  glands. 
In  Kollikers  opinion,  the  development  of  colourless  and  also 
coloured  corpuscles  of  the  blood  is  one  of  the  essential  functions 
of  the   spleen,  into  the  veins  of  which  the  new-formed   corpuscles 


chap,  xiv.]  FUNCTIONS  OF  THE   SPLEEN.  465 

.  and  are   thus    conveyed   into  the  genera]    current  of  the 
circulation. 

(3.)   There  LB   reason    to  believe,  that  in  the  spleen  many  of  the 

red  corpuscles  of  the  blood,  those  probably  which  have  discharged 
their  office  and  are  worn  out,  undergo  disintegration ;  for  in  the 
coloured  portions  of  the  spleen-pulp  an  abundance  of  such  cor- 
puscles, in  various  stages  of  degeneration,  arc  found,  while  the 
red  corpuscles  in  the  splenic  venous  blood  arc  said  to  he  relatively 
diminished.  This  process  appears  to  be  as  follows.  The  blood- 
corpuscles,  becoming  smaller  and  darker,  collect  together  in 
roundish  heaps,  which  may  remain  in  this  condition,  or  become 
each  surrounded  by  a  cell-wall.  The  cells  thus  produced  may 
contain  from  one  to  twenty  blood-corpuscles  in  their  interior. 
These  corpuscles  become  smaller  and  smaller  ;  exchange  their  red 
for  a  golden  yellow,  brown,  or  black  colour ;  and  at  length,  are 
converted  into  pigment-granules,  which  by  degrees  become  paler 
and  paler,  until  all  colour  is  lost.  The  corpuscles  undergo  these 
changes  whether  the  heaps  of  them  are  enveloped  by  a  cell-wall 
or  not. 

(4.)  From  the  almost  constant  presence  of  uric  acid,  as  well  as 
of  the  nitrogenous  bodies,  xanthin,  hypoxanthin,  and  leucin,  in 
the  spleen,  some  nitrogenous  metabolism  may  be  fairly  inferred 
to  occur  in  it. 

(5.)  Besides  these,  its  supposed  direct  offices,  the  spleen  is 
believed  to  fulfil  some  purpose  in  regard  to  the  portal  circulation, 
with  which  it  is  in  close  connection.  From  the  readiness  with 
which  it  admits  of  being  distended,  and  from  the  fact  that  it  is 
generally  small  while  gastric  digestion  is  going  on,  and  enlarges 
when  that  act  is  concluded,  it  is  supposed  to  act  as  a  kind  of 
vascular  reservoir,  or  diverticulum  to  the  portal  system,  or  more 
particularly  to  the  vessels  of  the  stomach.  That  it  may  serve 
such  a  purpose  is  also  made  probable  by  the  enlargement  which 
it  undergoes  in  certain  affections  of  the  heart  and  liver,  attended 
with  obstruction  to  the  passage  of  blood  through  the  latter  organ, 
and  by  its  diminution  when  the  congestion  of  the  portal  system 
is  relieved  by  discharges  from  the  bowels,  or  by  the  effusion  of 
blood  into  the  stomach.  This  mechanical  influence  on  the  circu- 
lation, however,  can  hardly  be  supposed  to  be  more  than  a  very 
subordinate  function. 

H    H 


466 


THE  VASCULAR   GLANDS. 


[CHAP.  XIV. 


Tt  is  only  necessary  to  mention  that  Schiff  believes  that  the  spleen  manu- 
factures a  substance  without  which  the  pancreatic  secretion  cannot  act  upon 
proteids,  so  that  when  the  spleen  is  removed  the  digestive  action  of  the 
pancreas  is  stopped. 


Influence  of  the  Nervous  System  upon  the  Spleen.— 
When  the  spleen  is  enlarged  after  digestion,  its  enlargement  is 
probably  due  to  two  causes,  (i)  a  relaxation  of  the  muscular 
tissue  which  forms  so  large  a  part  of  its  framework  ;  (2)  a  dilata- 
tion of  the  vessels.  Both  these  phenomena  are  doubtless  under 
control  of  the  nervous  system.  It  has  been  found  by  experiment 
that  when  the  splenic  nerves  are  cut  the  spleen  enlarges,  and  that 
contraction  can  be  brought  about  (1)  by  stimulation  of  the  spinal 

cord  (or  of  the  divided  nerves) ; 
(2)  reflexly  by  stimulation  of  the 
central  stumps  of  certain  divided 
nerves,  e.g.,  vagus  and  sciatic  ;  (3) 
by  local  stimulation  by  an  electric 
current ;  (4)  the  exhibition  of 
quinine  and  some  other  drugs.  It 
has  been  shown  by  means  of  a 
modification  of  the  plethysmo- 
graph  (Roy),  that  the  spleen  un- 
dergoes rhythmical  contractions 
and  dilatations,  due  no  doubt  to 
the  contraction  and  relaxation  of 
the  muscular  tissue  in  its  capsule 
and  trabecule.  The  gland  also 
shows  the  rhythmical  alteration 
of  the  general  blood  pressure  but 
to  a  less  extent  than  the  kidney. 


Fig.  255. — Transverse  section  of  a  lobule  of 
an  injected  infantile  thymus  gland,  n,  cap- 
sule of  connective-tissue  surrounding 
the  lobule  ;  b,  membrane  of  the  glandu- 
lar vesicles  ;  r,  cavity  of  the  lobule,  from 
which  the  larger  blood-vessels  are  seen 
to  extend  towards  and  ramify  in  the 
spheroidal  masses  of  the  lobule,  x  30. 
(Kulliker.) 


The    Thymus. 
This    gland    must    be    looked 


upon  as  a  temporary  organ,  as  it 
attains  its  greatest  size  early  after  birth,  and  after  the  second 
year  gradually  diminishes,  until  in  adult  life  hardly  a  vestige  re- 
mains. At  its  greatest  development  it  is  a  long  narrow  body, 
situated  in  the  front  of  the  chest  behind  the  sternum  and  partly 


chap,  xiv.l  STRUCTURE  01    THYMUS. 


467 


in  the  lower  part  of  the  neck.     It  is  of  a  reddish  or  greyish  colour, 
distinctly  tabulated. 

Structure. — The  gland    is  Burrounded    by   a  fibrous  capsule 
which  sends  in  processes,  forming  trabecule,   which  divide  the 

gland  into  Lobes,  and  carry  the  U 1-  and  lymph-vessels.     The 

trabecules  branch  into  small  ones,  which  divide  the  lobes  into 
lobules.     The  gland  is  encased  in  a  fold  of  the  pleura.    The  lobules 
are  further  subdivided  into  follicles  by  tine 
connective  tissue.    A  follicle  (fig.  256)  is  more  .  ..... 

or  less  polyhedral  in  shape,  and  consists  of 

cortical  and  medullary  portions,  the  structure 

of  both  being  of  adenoid  tissue,  but  in  the     $%i^j0^$&*G0& 

medullary  portion  the  matrix  is  coarse)',  and  - 

is  not  so  filled  up  with  lymphoid  corpuscles 

as  in  the  cortex.     The  adenoid  tissue  of  the        *• 

cortex,  and  to  a  less  marked  extent  in   the  p": 

medulla,  consists  of  two  kinds  of  tissue,  one    Fi„  2.6  _Frohlo  ,t0r!20„. 

with  small  meshes  formed  of  fine  fibres  with 

thickened  nodal  points,  and  the  other  enclosed       Pitied '''sh^in^^tho 

within  the  first,  composed  of  branched  con-       centre  afoUicie  of  poiy- 

'  -t  gxmal  shape  vnth  simi- 

nective  tissue  corpuscles  (Watney).  Scattered  jady  ^p^ef°m!^| 
in  the  adenoid  tissue  of  the  medulla  are  the  Noble  Smith  . 
concentric  corpuscles  of  H assail,  which  are  pro- 
toplasmic masses  of  various  sizes,  consisting  of  a  central  nucleated 
granular  centre,  surrounded  by  flattened  nucleated  endothelial 
cells.  In  the  reticulum,  especially  of  the  medulla,  are  large 
transparent  giant  cells.  In  the  thymus  of  the  dog  and  of  other 
animals  are  to  be  found  cysts,  probably  derived  from  the  con- 
centric corpuscles,  some  of  which  are  lined  with  ciliated  epithe- 
lium, and  others  with  short  columnar  cells.  Haemoglobin  is  found 
in  the  thymus  of  all  animals,  either  in  these  cysts,  or  in  cells 
near  to  or  of  the  concentric  corpuscles.  In  the  lymph  issuing 
from  the  thymus  are  found  cells  containing  coloured  blood  cor- 
puscles and  haemoglobin  granules,  and  in  the  lymphatics  of  the 
thymus  there  are  more  colourless  cells  than  in  the  lymphatics  of 
the  neck.  In  the  blood  of  the  thymic  vein,  there  appears  s«  >me- 
times  to  be  an  increase  in  the  colourless  corpuscles  and  also  masses 
of  granular  matter  (corpuscles  of  Zimmermann)  (Watney). 
The    arteries   radiate   from   the    centre   of    the  gland.       Lymph 

h  h  2 


463  THE  VASCULAR  GLANDS.  [chap.  xiv. 

sinuses  may  be  seen  occasionally  surrounding  a  greater  or  smaller 
portion  of  the  periphery  of  the  follicles  (Klein).  The  nerves  are 
very  minute. 

Function. — The  thymus  appears  to  take  part  in  producing 
coloured  corpuscles,  both  from  the  large  corpuscles  containing 
haemoglobin,  and  also  indirectly  from  the  colourless  corpuscles 
(Watney).  Respecting  the  function  of  the  gland  in  the  hyber- 
nating  animals,  in  which  it  exists  throughout  life ;  as  each 
successive  period  of  hybernation  approaches,  the  thymus  greatly 
enlarges  and  becomes  laden  with  fat,  which  accumulates  in  it 
and  in  fat-glands  connected  with  it,  in  even  larger  propor- 
tions than  it  does  in  the  ordinary  seats  of  adipose  tissue.  Hence 
it  appears  to  serve  for  the  storing  up  of  materials  which,  being 
re-absorbed  in  inactivity  of  the  hybernating  period,  may  maintain 
the  respiration  and  the  temperature  of  the  body  in  the  reduced 
state  to  which  they  fall  during  that  time. 


The  Thyroid. 

The  Thyroid  gland  is  situated  in  the  neck.  It  consists  of  two 
lobes  one  on  each  side  of  the  trachea  extending  upwards  to  the 
thyroid  cartilage,  covering  its  inferior  cornu  and  part  of  its 
body )  these  lobes  are  connected  across  the  middle  line  by  a 
middle  lobe  or  isthmus.  The  thyroid  is  covered  by  the  muscles 
of  the  neck.  It  is  highly  vascular,  and  varies  in  size  in  different 
individuals. 

Structure. — The  gland  is  encased  in  a  thin  transparent  layer 
of  dense  areolar  tissue,  free  from  fat,  containing  elastic  fibres. 
This  capsule  sends  in  strong  fibrous  trabecular,  which  enclose  the 
thyroid  vesicles — which  are  rounded  or  oblong  irregular  sacs,  con- 
sisting of  a  wall  of  thin  hyaline  membrane  lined  by  a  single  layer 
of  low  cylindrical  or  cubical  cells.  These  vesicles  are  filled  with 
a  coagulable  fluid  or  transparent  colloid  material.  The  colloid 
substance  increases  with  age,  and  the  cavities  appear  to  coalesce. 
In  the  interstitial  connective  tissue  is  a  round  meshed  capillary 
plexus  and  a  large  number  of  lymphatics.  The  nerves  adhere 
closely  to  the  vessels. 

In  the  vesicles  there  are  in   addition  to  the  yellowish  glassy 


CHAP.  XIV.] 


SUPRA-BENAL  CAPSULES. 


469 


colloid  material,  epithelium  cells,  colourless  blood  corpuscles,  and 
also  coloured  corpuscles  undergoing  disintegration. 


~ — ? 


Fig.  257. — Part  of  a  section  0/ the  human  Thyroid,  a,  fibrous  capsule;  b,  thyroid  vesicles 
filled  with,  e,  colloid  substance ;  c,  supporting  fibrous  tissue  ;  d,  short  columnar  cells 
lining  vesicles  ;  /,  arteries  ;  g,  veins  filled  with  blood  ;  h,  lymphatic  vessel  filled  with 
colloid  substance.      (S.  K.  Alcock). 

Function. — There  is  little  known  definitely  about  the  function 
of  the  thyroid  body.  It,  however,  produces  the  colloid  material  of 
the  vesicles,  which  is  carried  off  by  the  lymphatics  and  discharged 
into  the  blood,  and  so  may  contribute  its  share  to  the  elaboration 
of  that  fluid.  The  destruction  of  red  blood-corpuscles  is  also  sup- 
posed to  go  on  in  the  gland. 

Supra-renal  Capsules  or  Adrenals. 

These  are  two  flattened,  more  or  less  triangular  or  cocked-hat 
shaped  bodies,  resting  by  their  lower  border  upon  the  upper  border 
of  the  kidneys. 

Structure. — The  gland  is  surrounded  "by  an  outer  sheath  of 
connective  tissue,  which  sometimes  consists  of  two  layers,  sending 


470 


THE  VASCULAR   GLANDS. 


[chap.  XIV. 


in  exceedingly  fine  prolongations  forming  the  framework  of  the 
gland.  The  gland  tissue  proper  consists  of  an  outside  firmer 
cortical  portion,  and  an  inside  soft  dark  medullary  portion,  (i.) 
The  cortical  portion  is  divided  into  (fig.  258b)  an  external  narrow 
layer  of  small  rounded  or  oval  spaces,  the  zona  glomerulosa, 
made  by  the  fibrous  trabecular,  containing  multinucleated  masses 
of  protoplasm,  the  differentiation  of  which  into  distinct  cells 
cannot  be  made  out.  (b)  A  layer  of  cells  arranged  radially,  the 
zona  /"scicu/ata  (c).  The  substance  of  this  layer  is  broken  up  into 
cylinders,  each  of  which  is  surrounded  by  the  connective  tissue 
framework.  The  cylinders  thus  produced  are  of  three  kinds — one 
containing  an  opaque,  resistant,  highly  refracting  mass  (probably 
of  a  fatty  nature) ;  frequently  a  large  number  of  nuclei  are  present ; 
the  individual  cells  can  only  be  made  out  with  difficulty.  The 
second  variety  of  cylinders  is  of  a  brownish  colour,  and  contains 
finely  granular  cells,  in  which  are  fat  globules.  The  third  variety 
consists  of  grey  cylinders,  containing  a  number  of  cells  whose 
nuclei  are  filled  with  a  large  number  of  fat  granules.     The  third 


— ?'_ 


m 


\i  9  « 

I    '     - 


-  ■© 


, 


1       3'Q 


-    - 


c 


m  ■ 


a 


I    §  8 


0    §) 


m  A 


Fig.  258.  -  Vertical  section  through  part  of  the  cortical  portion  of  supra-renal  of  guinea-pig. 
a.  capsule;  b,  zona  glomerulosa,  c,  zona  fasieulata ;  rf,  connective  tissue  supporting 
the  columns  of  the  cells  of  the  latter,  and  also  indicating  the  position  of  the  blood- 
vessels.   (S.  K.  Alcock) . 

layer  of  the   cortical  portion  is  the  zona   reticularis  (not   shown 


ohap.  xiv.]  SUPBA-EENAL  CAPSULES.  47 1 

in  fig.  258).  This  layer  is  apparently  formed  by  the  breaking 
up  of  the  cylinders,  the  elements  being  dispersed  and  isolated 

The  cells  are  finely  granular,  and  have  no  deposit  of  Eat  in  their 
interior  ;  but  in  some  specimens  fat  may  be  present,  as  well  as 
certain  large  yellow  granules,  which  may  lie  called  pigment 
granuL 

(2.)  The  medullary  substance  consists  of  a  coarse  rounded  or 
pilar  mesh  work  of  fibrous  tissue,  in  the  alveoli  of  which  are 
3es  <>f  multinucleated  protoplasm  (fig.  259);  numerous  blood - 


..6:      '    '.;»•: 


Fig.  259. — Section  through  a  portion  of  t/>>  medullary  part  of  the  supra-renal  'of  guinea-pin-. 
The  vessels  are  veiy  numerous,  and  the  fibrous  stroma  more  distinct  than  in  the 
cortex,  and  is  moreover  reticulated.  The  cells  are  irregular  and  larger,  clean,  and 
free  from  oil  globules.     (S.  K.  Alcock). 

vessels  ;  and  an  abundance  of  nervous  elements.  The  cells  are 
very  irregular  in  shape  and  size,  poor  in  fat,  and  occasionally 
branched;  the  nerves  11m  through  the  cortical  substance,  and 
anastomose  over  the  medullary  portion. 

Function. — Of  the  function  of  the  supra-renal  bodies  nothing- 
can  be  definitely  stated,  but  they  are  in  all  probability  connected 
with  the  lymphatic  system. 

Addison  a  Dix<axc. — The  collection  of  large  numbers  of  cases  in  which  the 
supra- renal  capsules  have  l>een  diseased,  has  demonstrated  the  very  close 
relation  subsisting  between  disease  of  those  organs  and  brown  discoloration 
of  the  skin  (Addison's  disease);  but  the  explanation  of  this  relation  is  still 
involved  in  obscurity,  and  consequently  does  not  aid  much  in  determining 
the  functions  of  the  supra-renal  capsules. 


472  THE  VASCULAR   GLANDS.  [chap.  xiv. 

Pituitary  Body. 

This  body  is  a  small  reddish-grey  mass,  occupying  the  sella 
turcica  of  the  sphenoid  bone. 

Structure. — It  consists  of  two  lobes — a  small  posterior  one, 
consisting  of  nervous  tissue  ;  an  anterior  larger  one,  resembling 
the  thyroid  in  structure.  A  canal  lined  with  flattened  or  with 
ciliated  epithelium,  passes  through  the  anterior  lobe  ;  it  is  con- 
nected with  the  infundibulum.  The  gland  spaces  are  oval, 
nearly  round  at  the  periphery,  spherical  towards  the  centre  of  the 
organ ;  they  are  filled  with  nucleated  cells  of  various  sizes  and 
shapes  not  unlike  ganglion  cells,  collected  together  into  rounded 
masses,  filling  the  vesicles,  and  contained  in  a  semi-fluid  granular 
substance.  The  vesicles  are  enclosed  by  connective  tissue,  rich  in 
capillaries. 

Function. — Nothing  is  known  of  the  function  of  the  pituitary 
body. 

Pineal  Gland. 

This  gland,  which  is  a  small  reddish  body,  is  placed  beneath 
the  back  part  of  the  corpus  callosum,  and  rests  upon  the  corpora 
quadrigemina  (fig.  327,  g). 

Structure. — It  contains  a  central  cavity  lined  with  ciliated 
epithelium.  The  gland  substance  proper  is  divisible  into — (1.)  An 
outer  cortical  layer,  analogous  in  structure  to  the  anterior  lobe 
of  the  pituitary  body  ;  and  (2)  An  inner  central  layer,  wholly 
nervous.  The  cortical  layer  consists  of  a  number  of  closed 
follicles,  containing  (a)  cells  of  variable  shape,  rounded,  elongated, 
or  stellate ;  (b)  fusiform  cells.  There  is  also  present  a  gritty 
matter  (a.cervulus  cerebri),  consisting  of  round  particles  aggregated 
into  small  masses.  The  central  substance  consists  of  white  and 
grey  matter.  The  blood-vessels  are  small,  and  form  a  very  deli- 
cate capillary  plexus. 

Function. — Of  this  there  is  nothing  known. 

Functions  of  the  Vascular  Glands  in  General. 

The  opinion  that  the  vascular  glands  serve  for  the  higher 
organization  of  the  blood,  is  supported  by  their  being  all  especially 


CHAP,  xiv.]  VASCULAR   GLANDS    I.\    GENERAL,  473 

active  in  the  discharge  of  their  functions  during  foetal  life  and 
childhood,  when,  for  the  development  ami  growth  of  the  bodv, 
the  most  abundant  supply  «>f  highly  organised  blood  is  necessary. 

The  bulk  of  the  thymus  gland,  in  proportion  to  that  of  the  body, 
appears  to  bear  almost  a  direct  proportion  to  the  activity  of  the 
body's  development    and   growth,  and   when,   at    the   period    of 

puberty,  the  development  of  the  body  may  lie  said  to  be  complete, 
the  gland  wastes,  and  finally  disappears.  The  thyroid  gland  and 
supra-renal  capsules,  also,  though  they  probably  never  cease  to 
discharge  some  amount  of  function,  yet  are  proportionally  much 
smaller  in  childhood  than  in  fatal  life  and  infancy  ;  and  with  the 
years  advancing  to  the  adult  period,  they  diminish  yet  more  in 
proportionate  size  and  apparent  activity  of  function.  The  spleen 
more  nearly  retains  its  proportionate  size,  and  enlarges  nearly  as 
the  whole  body  does. 

The  vascular  glands  seem  not  essential  to  life,  at  least  not  in 
the  adult.  The  thymus  wastes  and  disappears  :  no  signs  of 
illness  attend  some  of  the  diseases  which  wholly  destroy  the 
structure  of  the  thyroid  gland ;  and  the  spleen  has  been  often 
removed  in  animals,  and  in  a  few  instances  in  men,  without  any 
evident  ill-consequence.  It  is  possible  that,  in  such  cases,  some 
compensation  for  the  loss  of  one  of  the  organs  may  be  afforded  by 
an  increased  activity  of  function  in  those  that  remain. 

Although  the  functions  of  all  the  vascular  glands  may  be 
similar,  in  so  far  as  they  may  all  alike  serve  for  the  elaboration 
and  maintenance  of  the  blood,  yet  each  of  them  probably  dis- 
charges a  peculiar  office,  in  relation  either  to  the  whole  economy, 
or  to  that  of  some  other  organ.  Respecting  the  special  office  of 
the  thyroid  gland,  nothing  reasonable  can  be  suggested ;  nor  is 
there  any  certain  evidence  concerning  that  of  the  supra-renal 
capsules.  Bergman  believed  that  they  formed  part  of  the  sym- 
pathetic nervous  system  from  the  richness  of  their  nervous  supply. 
Kolliker  states  that  he  is  inclined  to  look  upon  the  two  parts  as 
functionally  distinct,  the  cortical  part  belonging  to  the  blood 
vascular  system,  and  the  medullary  to  the  nervous  system. 


474 


CAUSES  AND   PHENOMENA   OF  MOTION.       [chap.  xv. 


CHAPTER    XY. 


CAUSES    AND    PHENOMENA    OF    MOTION. 

Ix  the  animal  body,  motion  is  produced  in  these  several  ways  : 
(i.)  The  oscillatory  or  vibratory  movement  of  Cilia.  (2.)  Amoeboid 
and  certain  Molecular  movements.  (3.)  The  contraction  of  Mus- 
cular fibre. 

I.  Ciliary  Motion. 

Ciliary,  which  is  closely  allied  to  amoeboid  and  muscular  motion 
(p.  9),  consists  in  the  incessant  vibration  of  fine,  pellucid  pro- 
cesses, about  5-0V0  °f  an  mcn  l°n8'>  termed  cilia  (figs.   260,  261), 

situated  on  the  free  extremities  of  the 
cells  of  epithelium  covering  certain  sur- 
faces of  the  body. 

The  distribution  and  structure  of  ciliary 
epithelium  and  the  microscopic  appear- 
ances of  cilia  in  motion  have  been  already 
described  (pp.  29,  30). 

Ciliary  motion  is  alike  independent  of 
the  will,   of  the  direct  influence  of  the 
nervous  system,  and  of  muscular  contrac- 
tion.    It  continues  for  several  hours  after 
death  or  removal  from  the  bod}',  provided  the  portion  of  tissue 
under   examination   be    kept    moist.       Its    independence    of  the 

nervous  s}Tstem  is  shown  also  in  its  occur- 
rence in  the  lowest  invertebrate  animals 
apparently  unprovided  with  anything  ana- 
logous to  a  nervous  s}Tstem,  in  its  persist- 
ence in  animals  killed  by  prussic  acid,  by 
narcotic  or  other  poisons,  and  after  the 
direct  application  of  narcotics  to  the  ciliary 
surface,  or  the  discharge  of  a  Leyden  jar, 
or  of  a  galvanic  shock  through  it.  The 
vapour  of  chloroform  arrests  the  motion; 
but  it  is  renewed  011  the  discontinuance  of 
the  application  (Lister).  The  movement 
ceases  in  an  atmosphere  deprived  of  oxygen,  but  is  revived  on  the 


Fig.  260. — Splieroidal  ciliated 
cells  from  the  mouth  of  the 
frog :  magnified  300  dia- 
meters.    (Sharpey.) 


Fig.  261. — Colu  nnar  ciliated 
crlls  from  the  h  man  nasal 
vir-mbrane :  mu'nilied  300 
diameters.     (Si  arpey.) 


.  hap.  xv.]  AMCBBOID  MOTION,  475 

admission  of  this  gas.    Carbonic  acid  stops  the  movement     The 

contact  of  various  substances  will  stop  the  motion  altogether  \ 
but  this  seems  to  depend  chiefly  on  destruction  of  the  delicate 
substance  of  which  the  cilia  are  composed. 

Nature  of  Ciliary  Action. — Little  or  nothing  is  known  with 
certainty  regarding  the  nature  of  ciliary  action.  It  is  a  special 
manifestation  of  a  similar  property  to  that  by  which  the  other 
motions  of  animals  are  effected,  namely,  by  what  we  term  vital 
contractility  (Sharpey).  The  fact  of  the  more  evident  movements 
of  the  larger  animals  being  effected  by  a  structure  apparently 
different  from  that  of  cilia,  is  no  argument  against  such  a  suppo- 
sition. For,  if  wre  consider  the  matter,  it  will  be  plain  that  our 
prejudices  against  admitting  a  relationship  to  exist  between  the 
two  structures,  muscles  and  cilia,  rests  on  no  definite  ground  ;  and 
for  the  simple  reason,  that  we  know  so  little  of  the  manner  of 
production  of  movement  in  either  case.  The  mere  difference  of 
structure  is  not  an  argument  in  point ;  neither  is  the  presence  or 
absence  of  nerves.  For  in  the  foetus  the  heart  begins  to  pulsate 
when  it  consists  of  a  mass  of  embryonic  cells,  and  long  before 
either  muscular  or  nervous  tissue  has  been  differentiated.  The 
movements  of  both  muscles  and  cilia  are  manifestations  of  enevjy, 
by  certain  special  structures,  which  we  call  respectively  muscles 
and  cilia.  We  know  nothing  more  about  the  means  by  which  the 
manifestation  is  effected  by  one  of  these  structures  than  by  the 
other  :  and  the  mere  fact  that  one  has  nerves  and  the  other  has 
not,  is  no  more  argument  against  cilia  having  what  we  call  a  vital 
power  of  contraction,  than  the  presence  or  absence  of  stripes  from 
voluntary  or  involuntary  muscles  respectively,  is  an  argument  for 
or  against  the  contraction  of  one  of  them  being  vital  and  the  other 
not  so. 

As  a  special  sub-division  of  ciliary  action  may  be  mentioned  the 
motion  of  spermatozoa  (fig.  403),  which  may  be  regarded  as  cells 
with  a  single  cilium. 

II.  Amoeboid  Motion. 

The  remarkable  movements  observed  in  colourless  blood  cor- 
puscles, connective  tissue  corpuscles,  and  many  other  cells  (p.  9), 
must  be  regarded  as  depending  on  a  kind  of  contraction  of  portions 
of  their  mass  very  similar  to  muscular  contraction. 

There  is  certainly  an  analogy  between  the  spherical  form  as- 


4/6 


CAUSES   AND   PHENOMENA   OF   MOTION.       [chap.  xv. 


sumed  by  a  colourless  blood-corpuscle  on  electric  stimulation  and 
the  condition  known  as  tetanus  in  muscles. 


III.  Muscular  Motion. 

Varieties  of  Muscular  Tissue. — There  are  two  chief  kinds 
of  muscular  tissue  :  (i.)  the  plain  or  non-striated,  and  (2.)  the 
striated,  and  they  are  distinguished  by  structural  peculiarities 
and  mode  of  action.  The  striped  form  of  muscular  fibre  is 
sometimes  called  voluntary  muscle,  because  all  muscles  under 
the  direct  control  of  the  will  are  constructed  of  it.  The  plain  or 
unstriped  variety  is  often  termed  involuntary,  because  it  alone  is 
found  in  the  greater  number  of  the  muscles  over  which  the  will 
has  no  power. 

(1.)  Plain  or  Unstriped  Muscle. 

Distribution. — Involuntary  muscle  forms  the  proper  muscular 
coats  (1.)  of  the  digestive  canal  from  the  middle  of  the  oesophagus 
to  the  internal  sphincter  ani ;  (2.)  of  the  ureters  and  urinary 
bladder;  (3.)  the  trachea  and  bronchi ;  (4.)  the  ducts  of  glands; 
(5.)  the  gall-bladder ;  (6.)  the  vesiculee  seminales;  (7.)  the  pregnant 
uterus;  (8.)  of  blood-vessels  and  lymphatics;  (9.)  the  iris,  and 
some  other  parts.    This  fonn  of  tissue  also  enters  (10.)  largely  into 

the  composition  of  the  tunica 
dartos,  and  is  the  principal 
cause  of  the  wrinkling  and  con- 
traction of  the  scrotum  on  ex- 
posure to  cold.  Unstriped  mus- 
cular tissue  occurs  largely  also 
(11.)  in  the  cutis  (p.  413),  being 
especially  abundant  in  the  in- 
terspaces between  the  bases  of 
the  papilla?.  Hence  when  it 
contracts  under  the  influence 
of  cold,  fear,  electricity,  or 
any  other  stimulus,  the  pa- 
pilla?  are  made  unusually  prominent,  and  give  rise  to  the 
peculiar  roughness  of  the  skin  termed  cutis  anserina,  or  goose 
skin.  It  occurs  also  in  the  superficial  portion  of  the  cutis,  in  all 
parts  where  hairs  occur,  in  the  form  of  flattened  roundish 
bundles,    which    lie    alongside    the    hair-follicles    and   sebaceous 


Fig.  262. —  Vertical  section  through  the  scalp 
with  two  hair-sacs  ;  c,  epidermis  ;  h,  cutis; 
c,  muscles  of  the  hair-follicles  (Kulliker, . 


,  hap.  xv.]        STRUCTURE   OF   UNSTRIPFT)    MUSf'LK. 


477 


glands.  They  pass  obliquely  from  without  inwards,  embrace  the 
Bebaceoua  -lands,  and  arc  attached  to  the  hair-follicles  near  their 
base  (fig.  228). 

Structure. — The  non-striated    muscles  are  made  up  of  elon- 
gated, spindle-shaped,  nucleated  fibre  cells  (fig.  263),  which  in  their 


Fig.  263.— A,  unstriped  muscle  cells  from  mesentery  of  newt,  sheath  with  transverse  marking 
faintly  seen,  x  180.  B,  from  similar  preparation,  showing- each  muscle  cell  con 
of  a  central  bundle  of  fibrils  (contractile  part)  connected  with  the  intranuclear  network 
and  a  sheath  with  annular  thickenings.  The  cells  show  varicosities  due  to  local  con- 
traction and  on  these  the  annular  thickenings  are  most  marked,  x  450.  (Klein  and 
Noble  Smith.) 

perfect  form  are  flat,  from  about  4  5\,  0  to  3al00  of  an  inch 
broad,  and  -^y  to  3-^  of  an  inch  in  length, — very  clear,  granular, 
and  brittle,  so   that  when  they  break  they  often  have   abruptly 


Fig.  264. — Plexus  of  bundles  0/  unstriped  muscle  cells  of  the  pulmonary  pleura  of  the  guinea- 
pig,     x  180.     (Klein  and  Noble  Smith.) 

rounded  or  square  extremities.  Each  muscle  cell  consists  of  a 
fine  sheath,  probably  elastic ;  of  a  central  bundle  of  fibrils 
representing  the  contractile  substance  ;  and  of  an  oblong  nucleus 


478 


CAUSES  AND   PHENOMENA   OF   MOTION.       [chap,  xy 


which  includes  within  a  membrane  a  fine  network  anastomosing 
at  the  poles  of  the  nucleus  with  the  contractile  fibrils.  The 
ends  of  fibres  are  usually  single,  sometimes  divided.  Between 
the  fibres  is  an  albuminous  cementing  material  (endomysium)  in 
which  are  found  connective  tissue  corpuscles,  and  a  few  fibres.  The 
perimysium  is  the  fibrous  connective  tissue  surrounding  and 
separating  the  bundles  of  muscle  cells. 


(2.)  Striated  or  Striped  Muscle. 

Distribution. — The  striated  muscles  include  the  whole  class  of 
voluntary  muscles,  the  heart,  and  those  muscles  neither  completely 
voluntary  nor  involuntary,  which  form  part  of  the  walls  of  the 
pharynx,  and  exist  in  many  other  parts  of  the  body,  as  the  internal 
ear,  urethra,  &c. 

Structure.- — All  these  muscles  are  composed  of  larger  or 
smaller  bundles  of  muscular  fibres  called  fasciculi,  enclosed  in 
coverings  of  fibro-cellular  tissue  (j^erimysium),  by  which  each  is  at 
once  connected  with  and  isolated  from  those  adjacent  to  it  (fig.  265). 

Supporting  the  fibres  con- 
tained in  each  fasciculus  is  a 
scanty  amount  of  fine  connec- 
tive tissue  (endomysium). 

Each  muscular  fibre  is  thus 
constructed  : — Externally  is  a 
fine,  transparent,  structureless 
membrane,  called  the  sarco- 
lemma  (fig.  266,  A),  which  in  the 
form  of  a  tubular  investing 
sheath  forms  the  outer  wall  of 
the  fibre,  and  is  filled  up  by  the 
contractile  material  of  which  the 
fibre  is  chiefly  composed.  Sometimes,  from  its  comparative  tough- 
ness, the  sarcolemma  will  remain  untorn,  when  by  extension  the 
contained  part  can  be  broken  (fig.  269),  and  its  presence  is  in 
this  way  best  demonstrated.  The  fibres,  which  are  cylindriform 
or  prismatic,  with  an  average  diameter  of  about  3^  of  an  inch, 
are  of  a  pale  yellow  colour,  and  apparently  marked  by  fine  strise, 
which  pass  transversely  round  them,  in  slightly  curved  or  wholly 
parallel  lines.     Each  fibre  is  found  to  consist  of  broad  dim  bands 


Fig.  265. — A  .small  portion  of  muscle,  natural 
size,  consisting  of 'larger  and  smaller  fasci- 
culi, seen  in  a  transverse  section,  and  the 
same  magnified  5  diameters  (Sharpey). 


en  LP.  xv.] 


STRIPED   MUSCLE. 


479 


(iIHiiiiiili! 


r 


of  highly  refractive  substance  representing  the  contractile 
portion  <>f  the  muscle  fibre — the  contractile  discs  (fig.  267,  A,  0) 
— alternating  with  narrow  bright  bands  of  a  less  refractive 
substance — the    interstitial    discs    (fig. 

267,  A,  /).  After  hardening,  each  con- 
tractile disc  becomes  longitudinally 
striated,  the  thin  oblong  rods  thus 
tunned  being  the  sarcous  elements  of 
Bowman.  The  sarcous  elements  are 
not  the  optical  units,  since  each  con- 
sists of  minute  doubly-refracting  ele- 
ments —  the  disdiaclasts  of  Brucke. 
When  seen  in  transverse  section  the 
contractile  discs  appear  to  be  sub- 
divided by  clear  lines  into  polygonal 
areas  Cohnheim's  fields  (fig.  271),  each 
corresponding  to  one  sarcous  element 
prism.  The  clear  lines  are  due  to  a 
transparent  interstitial  fluid  substance 
pressed  out  of  the  sarcous  elements 
when  they  coagulate.  There  is  still 
some  doubt  regarding  the  nature 
of  the  fibrils.  Each  of  them  appears 
to  be  composed  of  a  single  row  of 
minute  dark  quadrangular  particles, 
called  sarcous  elements,  which  are  sepa- 
rated from  each  other  by  a  bright  space 
formed  of  a  pellucid  substance  continu- 
ous   with    them.       Sharpey    believes 

that,  even  in  a  fibril  so  constituted,  the  ultimate  anatomical 
element  of  the  fibre  has  not  been  isolated.  He  believes  that 
each  fibril  with  quadrangular  sarcous  elements  is  composed  of  a 
number  of  other  fibrils  still  finer,  so  that  the  sarcous  element 
of  an  ultimate  fibril,  would  be  not  quadrangular  but  as  a  streak. 
In  either  case  the  appearance  of  striation  in  the  whole  fibre  would 
be  produced  by  the  arrangement,  side  by  side,  of  the  dark  and 
light  portions  respectively  of  the  fibrils  (fig.  267,  B,  </). 

A  fine  streak  can  usually  be  discerned  passing  across  the  inter- 
stitial disc  between  the  sarcous  elements  :  this  streak   is  termed 


Fig.  266. — Part  of  a  striped  muscle- 
fibre  of  a  water-beetle  (hydro- 
philus)  prepared  with  absolute 
alcohol.  A,  sarcolemma  ;  B, 
Krause's  membrane.  Owing 
to  contraction  during  harden- 
ing, the  sarcolemma  shows  re- 
gular bulgings.  Above  and 
below  Krause's  membrane  are 
seen  the  transparent  "lateral 
discs."  The  chief  mass  of  a 
muscular  compartment  is  occu- 
pied by  the  contractile  disc 
composed  of  sarcous  elements. 
The  substance  of  the  individual 
sarcous  elements  has  collected 
more  at  the  extremity  than  in 
the  centre :  hence  this  latter  is 
more  transparent.  The  optical 
effect  of  this  is  that  the  con- 
tractile disc  appears  to  possess 
a  "  median  disc  "  (Disc  of  Hen- 
sen)  .  Several  nuclei  of  muscle 
corpuscles,  C  and  D,  are  shown, 
and  in  them  a  minute  network. 
x  300.  (Klein  and  Noble 
Smith.' 


4So 


CAUSES   AXD   PHENOMENA   OF   MOTION.       [chap.  xv. 


Krause's  membrane  :  it  is  continuous  at  each  end  with  the  sarco- 
lemma  investing  the  muscular  fibre  (fig.  266,  B). 


55V     m 


Fi<*.  267. A.  Portion  of  a  medium-sized  human  muscular  fibre.    X  Soo.    B.  Separated  bundles 

of  fibrils  equally  masnified  :  r/.  ^.  larger,  and  6,  &,  smaller  collections  :  c,  still  smaller  : 
d  d  the  smallest  which  could  be  detached,  possibly  representing  a  single  series  of 
sarc'ous  elements  :  Sharp 

Thus  the  space  enclosed  by  the  sarcolemma  is  divided  into  a 
series  of  compartments  by  the   transverse  partitions  known   as 
Krause's  membranes ;  these  compartments  being 
,-,.  occupied  by  the   true  muscle  substance.      On 

each  side  (above  and  below)  of  Krause's  mem- 
brane is  a  bright  border  (lateral  disc).  In  the 
centre  of  the  dark  zone  of  sarcous  elements  a 
lighter  band  can  sometimes  be  dimly  discerned  : 
this  is  termed  the  middle  disc  of  Hensen  (see 
fig.  266,  A). 

In  some  fibres,  chiefly  those  from  insects, 
each  lateral  disc  contains  a  row  of  bright 
granules  forming  the  granular  layer  of  Flogel. 
The  fibres  contain  nuclei,  which  are  roundish 
ovoid,  or  spindle-shaped  in  different  animals. 
These   nuclei  are  situated  close  to   the  sarco- 


Mm 


(VJ-.v:.v» 


Fig.  268. —  Trea 
section  of  a  muscle- 
fibre  of  u-ater- 
(hydrophilus  pis- 
ceus),  showing  the 
position  of  the  mus- 
cle nuclei  "Walter 
Pye). 


OHAP.  XV.] 


STRIPED    MUSCLE. 


481 


lemma,  their  long  axes  being  parallel  to  the  fibres  which  contain 
them.     Each  nucleus  is  composed  of  a  uniform  network  of  fibril* 


Fig.  269.— Muscular  flbn   torn  across;  the  sarcolemma  still  connecting  the  two  parts  of  the 

fibre  (Todd  and  Bowman). 

and  is  embedded  in  a  thin,  more  or  less  branched  film  of  protoplasm. 
The  nucleus  and  protoplasm  together  form  the  muscle  cell  or 
///  >'scfe  corpuscle  of  Max  Schultze. 


jrjo.  270  —Section  through  the  muscular  substance  of  the  tongue,  with  capillaries  injected,  their 
° 'meshes  running  parallel  to  the  fibres.    Three  muscular  fibres  are  seen  running  longi- 
tudinally, and  two  bundles  of  fibres  in  transverse  section,     x  150.     (Klein  and  Noble 
Smith.) 

The    sarcous  elements    and    Krause's   membranes  are  doubly 
refracting,  the  rest  of  the  fibre  singly  refracting  (Briicke). 


gfc  271.— Transverse  section  through  muscular  fibres  of  human  tongue  /the  fibres  appear  in 
transverse  section  of  different  sizes  owing  to  their  being  more  or  less  spindle-shaped. 
The  muscle-corpuscles  are  indicated  by  their  deeply-stained  nuclei  situated  at  the 
inside  of  the  sarcolemma.  Each  muscle-fibre  shows  the  "  Cohnheim  s  fields,  that  is 
the  sarcous  elements  in  transverse  section  separated  by  clear  (apparently  linear) 
interstitial  substance,     x  450.     (Klein  and  Noble  Smith.) 


482 


CAUSES    AND    PHENOMENA    OF    MOTION.      [chai\  xv. 


According  to  Schafer,  the  granules,  which  have  been  mentioned  on  either 
side  of  Krause's  membrane,  are  little  knobs  attached  to  the  ends  of  "  muscle- 
rods  ;  "  and  these  muscle-rods,  knobbed  at  each  end  and  imbedded  in  a 
homogeneous  protoplasmic  ground-substance,  form  the  substance  of  the 
muscles.  This  view,  however,  of  the  structure  of  muscle  requires  further 
confirmation  before  it  can  be  accepted. 

Although  each  muscular  fibre  may  be  considered  to  be  formed 
of  a  number  of  longitudinal  fibrils,  arranged  side  by  side,  it  is 
also  true  that  they  are  not  naturally  separate  from  each  other, 
there  being  lateral  cohesion,  if  not  fusion,  of  each  sarcous  element 
with  those  around  and  in  contact  with  it ;  so  that  it  happens 
that  there  is  a  tendency  for  a  fibre  to  split,  not  only  into 
separate  fibrils,  but  also  occasionally  into  plates  or  disks,  each  of 
which  is  composed  of  sarcous  elements  laterally  adherent  one  to 
another. 

Muscular  Fibres  of  the  Heart  (figs.  272  and  273)  form  the 
chief,  though  not  the  only  exception  to  the  rule,  that  involuntary 


Pig.E/2. — Muscular  fibres  from 

the  heart,  magnified,  snow- 
ing their  cross-stride,  divi- 
sions, and  junctions  (Kcil- 
liker). 


Fig.  273. — Network  of  muscular  fibres  (striated; 
from  the  heart  of  a  pig.  The  nuclei  of  the 
muscle-corpuscles  are  well  shown.  X  450. 
(Klein  and  Noble  Smith.) 


muscles  are  constructed  of  plain  fibres ;  but  although  striated  and 
ho  far  resembling  those  of  the  skeletal  muscles,  they  present 
these  distinctions  : — Each  muscular  fibre  is  made  up  of  elongated, 


CHAP.   XV 


DEVELOPMENT    OF    MUSCLE. 


433 


nucleated,  and    branched  cells,  the   nuclei  oi    amscle-corpaBclea 
being  centrally  placed  in  the  fibre.     The  fibres  are  finer  and  less 


Fig.  274. — Muscular  fibre  alls  from  the  heart.      E.  A.  Schiifer. 


distinctly  striated  than  those  of  the  voluntary  muscles ;  and  no 
sarcolemma  can  he  usually  discerned. 

Blood  and  Nerve  Supply. — The  voluntary  muscles  are  freely 
supplied  with  blood-vessels  :  the  capillaries  form  a  network  with 
oblong  meshes  around  the  fibres  on  the  outside  of  the  sarcolemma. 
No  vessels  penetrate  the  sarcolemma  to  enter  the  interior  of  the 
fibre  (fig.  270).  Nerves  also  are  supplied  freely  to  muscles  (pp. 
549,  554)  ;  the  voluntary  muscles  receiving  chiefly  nerves  from  the 
cerebro-spinal  system,  and  the  unstriped  muscles  from  the  sympa- 
thetic or  ganglionic  system. 

Development. — (1.)  Unstriped. — The  cells  of  unstriped  muscle 
:ire  derived  directly  from  embryonic  cells,  by  an  elongation  of  the 
cell,  and  its  nucleus ;  the  latter  changing  from  a  vesicular  to  a  rod 
shape. 

(2.)  Striped. — Formerly  it  was  supposed  that  striated  fibres  are 
formed  by  the  coalescence  of  several  cells,  but  recently  it  has  been 
proved,  that  each  fibre  is  formed  from  a  single  cell,  the  process 
involving  an  enormous  increase  in  size,  a  multiplication  of  the 
nucleus  by  fission,  and  a  differentiation  of  the  cell-contents  (Remak, 
Wilson  Fox).  This  view  differs  but  little  from  that  previously 
taken  by  Savory,  that  the  muscular  fibre   is  produced,  not   by 

1  1  2 


484  CAUSES    AXD    PHENOMENA    OF    MOTION,      [chap.  xv. 

multiplication  of  cells,  but  by  arrangement  of  nuclei  in  a  growing 
mass  of  protoplasm  (answering  to  the  cell  in  the  theory  just 
referred  to),  which  becomes  gradually  differentiated  so  as  to 
assume  the  characters  of  a  fully  developed  muscular  fibre. 

Growth  of  Muscle. — The  growth  of  muscles,  both  striated 
and  non-striated,  is  the  result  of  an  increase  both  in  the  number 
and  size  of  the  individual  elements. 

In  the  pregnant  uterus  the  fibre-cells  may  become  enlarged  to 
ten  times  their  original  length.  In  involution  of  the  uterus 
after  parturition  the  reverse  changes  occur,  accompanied  generally 
by  some  fatty  infiltration  of  the  tissue  and  degeneration  of  the 
fibres. 

Physiology  of  Muscle. 

Muscle  may  exist  in  three  different  conditions  ;  rest,  activity, 
and  rigor. 

I.  Rest. 

Physical  condition. — During  rest  or  inactivity  a  muscle  has  a 
slight  but  very  perfect  elasticity  ;  it  admits  of  being  considerably 
stretched ;  but  returns  readily  and  completely  to  its  normal 
length.  In  the  living  body  the  muscles  are  always  stretched  some- 
what beyond  their  natural  length,  they  are  always  in  a  condition 
of  slight  tension  ;  an  arrangement  which  enables  the  whole  force 
of  the  contraction  to  be  utilised  in  approximating  the  points  of 
attachment.  It  is  obvious  that  if  the  muscles  were  lax,  the  first 
part  of  the  contraction  till  the  muscle  became  tight  would  be 
wasted. 

There  is  no  doubt  that  even  in  a  condition  of  rest  oxygen  is 
being  abstracted  from  the  blood  and  carbonic  acid  given  out  by  a 
muscle  ;  for  the  blood  becomes  venous  in  the  transit,  and  since 
the  muscles  form  b}^  far  the  largest  element  in  the  composition 
of  the  body,  chemical  changes  must  be  constantly  going  on  in 
them  as  in  other  tissues  and  organs,  although  not  necessarily 
accompanied  by  contraction.  "When  cut  out  of  the  body  such 
muscles  retain  their  contractility  longer  in  an  atmosphere  of 
oxygen  than  in  an  atmosphere  of  hydrogen  or  carbonic  acid,  and 
during  life,  an  amount  of  oxygen  is  no  doubt  necessary  to  the 
manifestation  of  energy  as  well  as  for  the  metabolism  going  on  in 
the  resting-  condition. 


pHAP.  xv.]  COMPOSITION    OF    MUSCLE.  485 

Chemical  composition.  Tl  10  reaction  of  living  muscle  is  neutral 
or  slightly  alkaline.  The  substance  or  muscle  plasma  which  forms 
the  contractile  principal  element  in  its  composition  undergoes 
coagulation  when  the  muscle  is  removed  from  the  body,  and 
the  process  may  be  observed  if  the  coagulation  be  delayed 
by  <old.  If  the  muscles  of  a  frog  be  frozen,  minced  whilst  in 
that  condition,  and  reduced  to  a  pulp  by  being  rubbed  up  with  a 
1  per  cent,  solution  of  sodium  chloride,  the  temperature  of 
which  must  be  very  low,  on  filtration  in  the  cold,  a  colourless, 
somewhat  turbid  filtrate  separates  with  difficulty,  which  is  muscle 
plasma.  This  fluid  at  the  ordinary  temperature  of  the  air  under- 
goes a  coagulation  or  clotting,  by  which  it  is  separated,  as  in  the 
case  of  blood,  into  muscle-serum  and  muscle-clot.  The  latter,  how- 
ever, is  not  made  up  of  fibrin  but  of  myosin,  which  is  a  globulin 
(p.  846).  Myosin  may  also  be  obtained  from  dead  muscle  by 
subjecting  it,  after  all  the  blood,  fat,  fibrous  tissue,  and  substances 
soluble  in  water,  have  been  removed,  to  a  ten  per  cent,  solution 
of  sodium  chloride,  filtering  and  allowing  the  filtrate  to  drop 
into  a  large  quantity  of  water;  myosin  separating  out  as  a  white 
flocculent  precipitate.  Obtained  in  either  way,  viz.,  from  living 
or  dead  muscle,  myosin  is  soluble  in  dilute  saline  solutions,  and 
the  solution  undergoes  coagulation  at  a  lower  temperature  than 
serum  -  albumin  or  paraglobulin,  viz.,  at  131  ° — 1400  F. 
(550 — 6o°C).  It  is  coagulated  also  by  alcohol.  It  is  dissolved 
and  converted  into  acid-albumin  by  dilute  acid,  such  as  hydro- 
chloric. 

Muscle-serum  is  acid  in  reaction,  contains  serum-albumin  and 
several  other  proteids  as  well  as  other  bodies,  among  which  are 
fats  ;  free  acids,  especially  sarco-lactic,  formic,  and  acetic ;  glucose, 
glycogen  and  inosite  ;  kreatin,  hypoxanthin,  or  carnin,  taurin, 
and  other  nitrogenous  crystalline  bodies ;  many  salts,  of  which 
the  chief  is  potassium  phosphate ;  Carbonic  acid,  and  lastly 
Haemoglobin,  on  which  the  colour  of  muscles  partially  depends. 
There  are  also  traces  of  ferments,  pepsin  among  others. 

Electrical  Condition ;  Natural  muscle  currents.  —  In  muscles 
which  have  been  removed  from  the  body,  it  has  been  found  that 
electrical  currents  can  be  demonstrated  for  some  little  time, 
passing  from  point  to  point  on  their  surface ;  but  as  soon  as  the 
muscles  die  or  enter  into  rigor  mortis,  these  currents  disappear. 


486  CAUSES    AND    PHENOMENA    OF    MOTION,      [chap.  xv. 

The  method  of  demonstration  usually  employed  is  as  follows  : 
The  frog's  muscles  are  most  convenient  for  experiment,  and  a 
muscle  of  regular  shape,  in  which  the  fibres  are  parallel,  is 
selected.  The  ends  are  cut  off  by  clean  vertical  cuts,  and  the 
resulting  piece  of  muscle  is  called  a  regular  muscle  prism.  The 
muscle  prism  is  insulated,  and  a  pair  of  non-polarisable  electrodes 
connected  with  a  very  delicate  galvanometer  are  applied  to  various 
points  of  the  prism,  and  by  a  deflection  of  the  needle  to  a  greater 
or  less  extent  in  one  direction  or  another,  the  strength  and  direc- 
tion of  the  currents  in  the  piece  of  muscle  can  be  estimated. 
It  is  necessary  to  use  non-polarisable  and  not  metallic  electrodes 
in  this  experiment,  as  otherwise   there  is  no   certainty  that   the 


Pig.  275. — Diagram  of  Du  Bois  BeymoniX's  non-polarisable  electrodes,  a,  glass  tube  filled 
■with  a  saturated  solution  of  zinc  sulphate,  in  the  end,  r,  of  -which  is  china  clay  drawn 
out  to  a  point ;  in  the  solution  a  well  amalgamated  zinc  rod  is  immersed  and  connected 
by  means  of  the  wire  which  passes  through  a  with  the  galvanometer.  The  remainder 
of  the  apparatus  is  simply  for  convenient  application.  The  muscle  to  the  end  of  the 
second  electrode  is  to  the  right  of  the  figure. 

whole  of  the  current  observed  is  communicated  from  the  muscle 
and  is  not  derived  from  the  metallic  electrodes  themselves  in 
consequence  of  the  action  of  the  saline  juices  of  the  tissues  upon 
them.  The  form  of  the  non-polarisable  electrodes  is  a  modifica- 
tion of  Du  Bois  Reymond's  apparatus  (fig.  275),  which  consists  of 
a  somewhat  flattened  glass  cylinder  a,  drawn  abruptly  to  a  point 
and  fitted  to  a  socket  capable  of  movement  and  attached  to  a 
stand  A,  so  that  it  can  be  raised  or  lowered  as  required.  The 
lower  portion  of  the  cylinder  is  filled  with  china  clay  moistened 
with  saline  solution,  part  of  which  projects  through   its  drawn" 


rHAr.  xv.]        ELECTRICAL    CONDITION    OF    MUSCLE. 


487 


out  point  ;  the  rest  of  the  cylinder  is  fitted  with  a  saturated  solu- 
tion of  zinc  sulphate  into  which  dips  a  well  amalgamated  piece 
of  zinc  which  is  connected  by  means  of  a  wire  with  the  galva- 
nometer. In  this  way  the  zinc  sulphate  forms  an  homogeneous 
and  non-polarisable  conductor  between  the  zinc  and  the  china 
clay.  A  second  electrode  of  the  same  kind  is,  of  course, 
necessary. 

In  such  a  regular  muscle  prism  the  currents  are  found  to  be  as 
follows  : — 


Fig.  276. — Diagram  of  the  currents  in  a  muscle  prism.     (Du  Bois  Eeymond.) 

If  from  a  point  on  the  surface  a  line — the  equator — be  drawn 
across  the  muscle  prism  equally  dividing  it,  currents  pass  from 
this  point  to  points  away  from  it,  which  are  weak  if  the  points  are 
near,  and  increase  in  strength  as  the  points  are  further  and  further 
away  from  the  equator ;  the  strongest  passing  from  the  equator  to 
a  point  representing  the  middle  of  the  cut  ends  (fig.  276,  2) ; 
currents  also  pass  from  points  nearer  the  equator  to  those  more 
remote  (fig.  276,  1,  3,  4),  but  not  from  points  equally  distant,  or 
iso-electric  points  (fig.  276,  6,  7,  8).  The  cut  ends  are  always 
negative  to  the  equator.  These  currents  are  constant  for  some 
time  after  removal  of  the  muscle  from  the  body,  and  in  fact 
remain  as  long  as  the  muscle  retains  its  life.  They  are  in  all 
probability  due  to  chemical  change  going  on  in  the  muscles. 

The  currents  are  diminished  by  fatigue  and  are  increased  by  an 
increase  of  temperature  within  natural  limits.  If  the  uninjured 
tendon  be  used  as  the  end  of  the  muscle,  and  the  muscle  be 
examined  without  removal  from  the  body,  the  currents  are  very 
feeble,  but   they  are  at   once  much    increased  by  injuring   the 


488  CAUSES    AXD    PHENOMENA    OF    MOTION,      [chap.  xv. 

muscle,  as  by  cutting  off  its  tendou.  The  last  observation 
appeal's  to  show  that  they  are  right  who  believe  that  the  currents 
do  not  exist  in  muscles  uninjured  in  situ,  but  that  injury,  either 
mechanical,  chemical  or  thermal,  will  render  the  injured  part 
electrically  negative  to  other  points  on  the  muscle.  In  a  frog's 
heart  it  has  been  shown,  too,  that  no  currents  exist  during  its 
inactivity,  but  that  as  soon  as  it  is  injured  in  any  way  currents 
are  developed,  the  injured  part  being  negative  to  the  rest  of  the 
muscle.  The  currents  which  have  been  above  described  are 
called  either  natural  muscle  currents  or. currents  of  rest,  according 
as  they  are  looked  upon  as  always  existing  in  muscle  or  as  deve- 
loped when  a  part  of  the  muscle  is  subjected  to  injury  :  in  either 
case,  up  to  a  certain  point,  it  is  agreed  that  the  strength  of  the 
currents  is  in  direct  proportion  to  the  injury. 

II.  Activity. 

The  property  of  muscular  tissue,  by  which  its  peculiar  func- 
tions are  exercised,  is  its  contractility,  which  is  excited  by  all 
kinds  of  stimuli  applied  either  directly  to  the  muscles,  or  indirectly 
to  them  through  the  medium  of  their  motor  nerves.  This  pro- 
perty, although  commonly  brought  into  action  through  the 
nervous  system,  is  inherent  in  the  muscular  tissue.  For — (i).  it 
may  be  manifested  in  a  muscle  which  is  isolated  from  the  influence 
of  the  nervous  system  by  division  of  the  nerves  supplying  it,  so 
long  as  the  natural  tissue  of  the  muscle  is  duly  nourished ;  and 
(2).  it  is  manifest  in  a  portion  of  muscular  fibre,  in  which,  under 
the  microscope,  no  nerve-fibre  can  be  traced.  (3).  Substances 
such  as  vrari,  Avhich  paralyse  the  nerve-endings  in  muscles,  do 
not  at  all  diminish  the  irritability  of  the  muscle.  (4).  When  a 
muscle  is  fatigued,  a  local  stimulation  is  followed  by  a  contraction 
of  a  small  part  of  the  fibre  in  the  immediate  vicinity  without  any 
regard  to  the  distribution  of  nerve-fibres. 

If  the  removal  of  nervous  influence  be  long  continued,  as  by 
division  of  the  nerves  supplying  a  muscle,  or  in  cases  of  paralysis 
of  long-standing,  the  irritability,  i.e.,  the  power  of  both  per- 
ceiving and  responding  to  a  stimulus,  may  be  lost  ;  but  probably 
this  is  chiefly  due  to  the  impaired  nutrition  of  the  muscular 
tissue,  which  ensues  through  its  inaction.  The  irritability  of 
muscles  is  also  of  course  soon  lost,  unless  a  supply  of  arterial 


•iiAi-.  xv.]  KTJSCULAB    CONTRACTION.  489 

blood  to  them  is  kept  up.  Thus,  after  ligature  of  the  main 
arterial  trunk  of  a  limb,  the  power  of  moving  the  muscles  is  par- 
tially or  wholly  lost,  until  thr  collateral  circulation  is  established  ; 
and  when,  in  animals,  the  abdominal  aorta  is  tied,  the  hind  legs 
are  rendered  almost  powerless. 

The  same  fact  may  be  readily  shown  by  compressing  the  abdo- 
minal aorta  in  a  rabbit  for  about  10  minutes;  if  the  pressure  be 
released  and  the  animal  be  placed  on  the  ground,  it  will  work 
itself  along  with  its  front  legs,  while  the  hind  legs  sprawl  help- 
lessly behind.  Gradually  the  muscles  recover  their  power  and 
become  quite  as  efficient  as  before. 

So,  also,  it  is  to  the  imperfect  supply  of  arterial  blood  to  the 
muscular  tissue  of  the  heart,  that  the  cessation  of  the  action  of 
this  organ  in  asphyxia  is  in  some  measure  due. 

Sensibility. — Besides  the  property  of  contractility,  the  muscles, 
especially  the  striated,  possess  sensibility  by  means  of  the  sensory 
nerve-fibres  distributed  to  them.  The  amount  of  common  sensi- 
bility in  muscles  is  not  great;  for  they  may  be  cut  or  pricked 
without  giving  rise  to  severe  pain,  at  least  in  their  healthy  con- 
dition. But  they  have  a  peculiar  sensibility,  or  at  least  a  peculiar 
modification  of  common  sensibility,  which  is  shown  in  that  their 
nerves  can  communicate  to  the  mind  an  accurate  knowledge  of 
their  states  and  positions  when  in  action.  By  this  sensibility, 
we  are  not  only  made  conscious  of  the  morbid  sensations  of 
fatigue  and  cramp  in  muscles,  but  acquire,  through  muscular 
action,  a  knowledge  of  the  distance  of  bodies  and  their  relation 
to  each  other,  and  are  enabled  to  estimate  and  compare  their 
weight  and  resistance  by  the  effort  of  which  we  are  conscious 
in  measuring,  moving,  or  raising  them.  Except  with  such  know- 
ledge of  the  positiou  and  state  of  each  muscle,  we  could  not  tell 
how  or  when  to  move  it  for  any  required  action;  nor  without 
such  a  sensation  of  effort  could  we  maintain  the  muscles  in  con- 
traction for  any  prolonged  exertion. 

Muscular  Contraction. 

The  power  which  muscles  possess  of  contraction  may  be  called 
forth  by  stimuli  of  various  kinds,  viz.,  by  Mechanical,  Thermal, 
Chemical,  and  Electrical  means,  and   these   stimuli  may  also  be 


490  CAUSES    AND    PHENOMENA    OF    MOTION.      [chap.  xv. 

applied  directly  to  the  muscle  or  indirectly  to  the  nerve  supply- 
ing it.  There  are  distinct  advantages,  however,  in  applying  the 
stimulus  through  the  nerves,  as  it  is  more  convenient,  as  well  as 
more  potent. 

Mechanical  stimuli,  as  by  a  blow,  pinch,  prick  of  the  muscle  or 
its  nerve,  will  produce  a  contraction,  repeated  on  the  repetition 
of  the  stimulus  ;  but  if  applied  to  the  same  point  for  a  limited 
number  of  times  only,  as  such  stimuli  will  soon  destroy  the 
irritability  of  the  preparation. 

Thermal  stimuli. — If  a  needle  be  heated  and  applied  to  a  muscle 
or  its  nerve,  the  muscle  will  contract.  A  temperature  of  over 
ioo°F.  (37*8° C.)  will  cause  the  muscles  of  a  frog  to  pass  into  a 
condition  known  as  heat  rigor. 

Chemical  stimuli. — A  great  variety  of  chemical  substances 
will  excite  the  contraction  of  muscles,  some  substances  being 
more  potent  in  irritating  the  muscle  itself,  and  other  substances 
having  more  effect  upon  the  nerve.  Of  the  former  may  be  men- 
tioned, dilute  acids,  salts  of  certain  nietals,  e.;/.,  zinc,  copper  and 
iron  ;  to  the  latter  belong  strong  glycerin,  strong  acids,  ammonia 
and  bile  salts  in  strong  solution. 

Electrical  stimuli. — These  are  most  frequently  used  as  muscle 
stimuli,  as  the  strength  of  the  stimulus  may  be  more  conveniently 


Fig.  277. — Diagram  of  a  BanxtlVs  battery.     (After  Balfour  Stewart]. 

regulated.  The  kind  of  current  employed  may  be,  for  the  sake  of 
clearness,  treated  of  under  two  heads  : — (1)  The  continuous  current, 
and  (2)  The  induced  current.  (1)  The  continuous  current  is  sup- 
plied by  a  battery  such  as  that  of  Daniell,  by  which  an  electrical 
current   which   varies  but  little  in  intensity  is  obtained.      The 


ohaf.xt.]  MU8CULAB    CONTRACTION.  491 

battery  (fig.  277)  consists  of  a  positive  plate  of  irell-amalgamated 
one  immersed  in  ■  poroua  cell,  containing  dilute  sulphuric  acid  ; 
and  this  oell  is  again  contained  within  a  larger  copper  vessel  (form- 
ing the  negative  plate),  containing  saturated  solution  of 
oopper  sulphate.  The  electrical  current  is  made  continuous  by 
the  use  of  the  two  fluids  in  the  following  manner.  The  action  of 
the  dilute  sulphuric  acid  upon  the  zine  {date  partly  dissolves  it 
and  liberates  hydrogen,  and  this  gas  passes  through  the  porous 
I  ssel  and  decomposes  the  copper  sulphate  into  copper  and  sul- 
phuric acid.  The  former  is  deposited  upon  the  copper  plate  and 
the  latter  passes  through  the  porous  vessel  to  renew  the  sulphuric 
acid  which  is  being  used  up.  The  copper  sulphate  solution  is 
renewed  by  spare  cr}'stals  of  the  salt  which  are  kept  on  a  little 
shelf  attached  to  the  copper  plate  and  slightly  below  the  level  of 
the  solution  in  the  vessel.  The  current  of  electricity  supplied  by 
this  battery  will  continue  without  variation  for  a  considerable 
time.  Other  continuous-current  batteries  such  as  Grove's  may 
be  used  in  place  of  Daniell's.  The  way  in  which  the  apparatus 
is  arranged  is  to  attach  wires  to  the  copper  and  zinc  plates  and  to 
bring  them  to  a  key,  which  is  a  little  apparatus  for  connecting 
the  wires  of  a  battery.  One  often  employed  is  Du  Bois  Reymond's 
(fig.  280,  d)  ;  it  consists  of  two  pieces  of  brass  about  an  inch  long, 
in  each  of  which  are  two  holes  for  wires  and  binding  screws  to  fix 
them  tightly  ;  these  pieces  of  brass  are  fixed  upon  a  vulcanite  plate, 
to  the  under  surface  of  which  is  a  screw  clamp  by  which  it  can  1  le 
secured  to  the  table.  The  interval  between  the  pieces  of  brass  can 
be  bridged  over  by  means  of  a  third  thinner  piece  of  similar  metal 
fixed  by  a  screw  to  one  of  the  brass  pieces  and  capable  of  move- 
ment by  a  handle  at  right  angles,  so  as  to  touch  the  other  piece 
of  I  trass.  If  the  wires  from  the  battery  are  brought  to  the  inner 
binding  screws,  and  the  bridge  be  brought  to  connect  them,  the 
current  passes  across  it  and  back  to  the  battery.  Wires  are 
connected  with  the  outer  binding  screws,  and  the  other  ends  are 
approximated  for  about  two  inches,  but,  being  covered  except  at 
their  points,  are  insulated,  the  uncovered  points  are  about  an 
eighth  of  an  inch  apart.  These  wires  are  the  electrodes,  and  the 
electrical  stimulus  is  applied  to  the  muscle,  if  they  are  placed 
behind  its  nerve  and  the  connection  between  the  two  brass  plates 
of  the  key  be  broken  by  depressing  the  handle  of  the  bridge  and 


492  CAUSES    AND    PHENOMENA    OF    MOTION.      [chap.  xv. 

so  raising  the  connecting  piece  of  metal.  The  key  is  then  said 
to  be  opened.  (2)  The  induced  current. — An  induced  current  is 
developed  by  means  of  an  apparatus  called  an  induction  coil,  and 
the  one  employed  for  physiological  purposes  is  mostly  the  one 
(fig.  278). 


Fig.  278. — Du  Bois  Jiet/7no7id,s  induction  coiU 

Wires  from  a  battery  are  brought  to  the  two  binding  screws 
d'  and  d,  a  key  intervening.  These  binding  screws  are  the  ends 
of  a  coil  of  coarse  covered  wire  c,  called  the  primary  coil.  The 
ends  of  a  coil  of  finer  covered  wire  g,  are  attached  to  two  binding 
screws  to  the  left  of  the  figure,  one  only  of  which  is  visible.  This 
is  the  secondary  coil  and  is  capable  of  being  moved  nearer  to  c 
along  a  grooved  and  graduated  scale.  To  the  binding  screws 
to  the  left  of  g,  the  wires  of  electrodes  used  to  stimulate  the 
muscle  are  attached.  If  the  key  in  the  circuit  of  wires  from  the 
battery  to  the  primary  coil  (primary  circuit)  be  closed,  the  current 
from  the  battery  passes  through  the  primary  coil  and  across  the 
key  to  the  battery  and  continues  to  pass  as  long  as  the  key  con- 
tinues closed.  At  the  moment  of  closure  of  the  key,  at  the 
exact  instant  of  the  completion  of  the  primary  circuit,  an  instan- 
taneous current  of  electricity  is  induced  in  the  secondary  coil,  g, 
if  it  be  sufficiently  near,  and  the  nearer  it  is  to  c,  the  stronger  is 
the  current.  The  induced  current  is  only  momentary  in  duration 
and  does  not  continue  during  the  whole  of  the  period  when  the 


CHAP.  w.  | 


MUSCULAK    CONTRACTION. 


493 


primary  circuit  is  complete.  When,  however,  the  primary  currenl 
is  broken  by  opening  the  key,  a  second,  also  momentary,  current 
is  induced  in  g.  The  former  induced  current  is  called  the  making, 
and    the   latter    the    breaking    shock  ;    the    former    is    in    the 

opposite  to,  and  the  latter  in  the  same  direction,  as  the  primary 
current. 

The  induction  coil  may  be  used  to  produce  a  rapid  Beriee  of 
shocks  by  means  of  another  and  accessory  part  of  the  apparatus 
at  the  right  of  the  fig.  If  the  wires  from  a  battery  are  connected 
with  the  two  pillars  by 
the  binding  screws,  one 
below  c,  and  the  other, 
a,  the  course  of  the  cur- 
rent is  indicated  in  fig. 
279,  the  direction  being- 
indicated  by  the  arrows. 
The  current  passes  up  the 
pillar  from  e,  and  along 
the  spring,  if  the  end  of 
d!  be  close  to  the  spring, 
and  the  current  passes 
to  the  primary  coil  c,  and 
to  wires  covering  two  upright  pillars  of  soft  iron,  from  them  to  the 
pillar  a,  and  out  by  the  wires  to  the  battery;  in  passing  along  the 
wire,  b,  the  soft  iron  is  converted  into  a  magnet  and  so  attracts 
the  hammer,  /,  of  the  spring,  breaks  the  connection  of  the  spring 
-with  d'  and  so  cuts  off  the  current  from  the  primary  coil  and  also 
from  the  electro-magnet.  As  the  pillars,  b,  are  no  longer  mag 
netized  the  spring  is  released  and  the  current  passes  in  the  first 
direction,  and  is  in  like  manner  interrupted.  At  each  make  and 
break  of  the  primary  current,  currents  corresponding  are  induced 
in  the  secondary  coil.  These  currents  arc,  as  before,  in  an 
opposite  direction,  but  are  not  equal  in  intensity,  the  break 
shock  being  greater.  In  order  that  the  shocks  should  be  about 
equal  at  the  make  and  break,  a  wire  (fig.  279,  e)  connects  e  and 
d\  and  the  screw  d'  is  raised  out  of  reach  of  the  spring,  and  d  is 
raised  (as  in  fig.  279),  so  that  part  of  the  current  always  p 
through  the  primary  coil  and  electro-magnet.  When  the  spring 
touches  d,   the   current  in  b  is    diminished,   but    never  entirely 


Fig-.  279. — Diagram  of  the  course  of  the  current  in  the 
magnetic  interrupter  of  Du  Bois  Reymond's  induction 
'■"'<■!.     (Helmholz's  modification.) 


494 


CAUSES    AND    PHENOMENA    OF    MOTION,      [chap.  xv. 


withdrawn,  and  the  primary  current   is  altered   in  intensity  at 
each  contact  of  the  spring  with  d,  but  never  entirely  broken. 

Record  of  Muscular  Contraction  under  Stimuli. 

The  muscles  of  the  frog  are  those  which  can  most  conveniently 
be  experimented  with  and  their  contractions  recorded.  The  frog 
is  pithed,  that  is  to  say  its  central  nervous  system  is  entirely 
destroyed  by  the  insertion  of  a  stout  needle  into  the  spinal  cord 


Fig.  280. — Arrangement  0/ the  apparatus  necessary  for  recording  muscle  contractions  yrith  a 
revolving  cylinder  carrying  smoked  paper.  A.  revolving  cylinder  ;  B,  the  frog  arranged 
upon  a  cork-covered  board  -which  is  capable  of  being  raised  or  lowered  on  the  upright, 
■which  also  can  be  moved  along  a  solid  triangular  bar  of  metal  attached  to  the  base  of 
the  recording  apparatus — the  tendon  of  the  gastrocnemius  is  attached  to  the  ■writing 
lever  properly  -weighted  by  a  ligature.  The  electrodes  from  the  secondary  coil  pass  to 
the  apparatus — being,  for  the  sake  of  convenience,  first  of  all  brought  to  a  key,  D 
(Du  Bois  Raymond's)  ;  C,  the  induction  coil  :  F,  the  battery  (in  this  fig.  a  bichromate 
one   ;  E,  the  key   Hone's]  in  the  primary  circuit. 

and  the  parts  above  it.  One  of  its  lower  extremities  is  used 
in  the  following  manner.  The  large  trunk  of  the  sciatic  nerve  is 
dissected  out  at  the  back  of  the  thigh,  and  a  pair  of  electrodes  is 


CHAP,  xv.]  MTJSCULAB    CONTRACTION.  495 

inserted  behind  it.  The  tendo-achillia  is  divided  from  its  attach- 
ment to  the  oe  oalcis,  and  a  ligature  is  tightly  tied  round  it.  This 
tendon  is  part  of  the  broad  muscle  of  the  thigh  (gastrocnemius) 

which  arises  from  above  the  OOndylea  of  the  femur.  The  femur  is 
now  fixed  to  a  board  covered  with  cork,  and  the  ligature  attached 

to  the* tendon  is  tied  to  the  upright  of  a  piece  of  metal  bent  at 
right  angles  (fig.  280,  h),  which  is  capable  of  movement  about 
pivot  at  its  knee,  the  horizontal  portion  carrying  a  writing  lever 
(myograph).  When  the  muscle  contracts  the  lever  is  raised.  It 
is  necessary  to  attach  a  small  weight  to  the  lever.  In  this 
arrangement  the  muscle  is  in  situ,  and  the  nerve  disturbed  from 
its  relations  as  little  as  possible. 

The  muscle  may,  however,  be  detached  from  the  body  with  the 
lower  end  of  the  femur  from  which  it  arises,  and  the  nerve  going 
to  it  may  be  taken  away  with  it.  The  femur  is  divided  at  about 
the  lower  third.  The  bone  is  held  in  a  firm  clamp,  the  nerve  is 
placed  upon  two  electrodes  connected  with  an  induction  appa 
fatus,  and  the  lower  end  of  the  muscle  is  connected  by  means  of 
a  ligature  attached  to  its  tendon  with  a  lever  which  can  write  on 
a  recording  apparatus. 

To  prevent  evaporation  this  so-called  nerve-muscle  preparation  is 
placed  under  a  glass  shade,  the  air  in  which  is  kept  moist  by 
means  of  blotting  paper  saturated  with  saline  solution. 

Effect  of  a  single  Induction  Shock. 

Taking  the  nerve-muscle  preparation  in  either  of  these  ways, 
on  closing  or  opening  the  key  in  the  primary  circuit  we  obtain 
and  can  record  a  contraction,  and  if  we  use  the  clockwork  appa- 
ratus revolving  rapidly,  a  curve  is  traced  such  as  is  shown  in 
(tig.  281). 

Another  way  of  recording  the  contraction  is  by  the  pendulum 
myograph  (fig.  282).  Here  the  movement  of  the  pendulum  along 
a  certain  arc  is  substituted  for  the  clockwork  movement  of  the 
other  apparatus.  The  pendulum  carries  a  smoked  glass  plate 
upon  which  the  writing  lever  of  a  myograph  is  made  to  mark. 
The  opening  or  breaking  shock  is  sent  into  the  nerve-muscle 
preparation  by  the  pendulum  in  its  swing  opening  a  key  (tig.  2S2, 
in  the  primary  circuit. 


496 


CAUSES    AXD    PHENOMENA    OF    MOTION,      [chap.  xv. 


Single  Muscle  Contraction. —  The  tracings  obtained  in  a 
manner  above  described  and  seen  in  fig.  281,  may  be  thus 
explained. 


pjo-,  281. — Muscle-curve  obtained  by  the  pendulum  myograph,  s,  indicates  the  exact  instant 
of  the  induction  shock  ;  c,  commencement ;  and  m  x,  the  maximum  elevation  of  lever ; 
t,  the  line  of  a  vibrating  tuning-fork.     (M.  Foster.) 


Fig.  282. — Simple  form  of  pendulum  myograph  and  accessory  parts.  A,  pivot  upon  which 
pendulum  swings;  B,  catch  on  lower  end  of  myograph  opening  the  key,  C,  in  its 
swing ;  D,  a  spring-catch  which  retains  myograph,  as  indicated  by  dotted  lines,  and 
on  pressing  down  the  handle  of  which  the  pendulum  swings  along  the  arc  to  D  on  the 
left  of  figure,  and  is  caught  by  its  spring. 


ojiap.  xv.]  MUSCULAR  CONTRACTION.  497 

The  upper  line  (m)  represents  the  curve  traced  by  the  end  of 
the  lever  after  stimulation  of  the  muscle  by  a  Bingle  induction- 
Bhock  :  the  middle  line  (/)  is  that  described  by  the  marking-lever, 

and  indicates  by  a  sudden  drop  the  exact  instant  at  which  the 
induction-shock  was  given.  The  lower  wavy  line  (t)  is  traced  by 
a  vibrating  tuning-fork,  and  serves  to  measure  precisely  the  inter- 
vals of  time  occupied  in  each  part  of  the  contraction. 

It  will  be  observed  that  after  the  stimulus  has  been  applied,  as 
indicated  by  the  vertical  line  *,  there  is  an  interval  before  the  con- 
traction commences,  as  indicated  by  the  line  c.  This  interval, 
termed  the  w  latent  period  "  (Helmholtz),  when  measured  by  the 
number  of  vibrations  of  the  tuning-fork  between  the  lines  s  and  c, 
is  found  to  be  about  y^y  sec. 

The  contraction  progresses  rapidly  at  first  and  afterwards  more 
slowdy  to  the  maximum  (the  point  in  the  curve  through  which 
the  line  mx  is  drawn),  which  takes  -^  sec,  and  then  the  muscle 
elongates  again  as  indicated  by  the  descending  curve,  at  first 
rapidly,  afterwards  more  slowly,  till  it  attains  its  original  length 
at  the  point  indicated  by  the  line  c,  occupying  y|o  sec- 

The  muscle  curve  obtained  from  the  heart  resembles  that  of 
unstriped  muscles  in  the  long  duration  of  the  effect  of  stimula- 
tion ;  the  descending  curve  is  very  much  prolonged. 


gfe  283.— Tracinq  of  a  double  muscle-curve.  To  be  read  from  left  to  right  .While  the 
muscle  was  engaged  in  the  first  contraction  (whose  complete  course,  had  nothing  inter- 
vened, is  indicated  by  the  dotted  line),  a  second  induction-shock  was  thrown  in,  at  such 
a  time  that  the  second  contraction  began  just  as  the  first  was  beginning  to  decline. 
The  second  curve  is  seen  to  start  from  the  first,  as  does  the  first  from  the  base  line. 
(M.  Foster.) 

The  greater  part  of  the  latent  period  is  taken  up  by  changes  in 
the  muscle  itself,  the  rest  being  occupied  in  the  propagation  of  the 
shock  along  the  nerve  (M.  Foster). 

K    K 


498  CAUSES   AND   PHENOMENA    OF   MOTION.      [chap.  xv. 

Tetanus. — If  instead  of  a  single  induction-shock  through  the 
preparation  we  pass  two,  one  immediately  after  the  other,  when 
the  point  of  stimulation  of  the  second  one  corresponds  to  the 
maximum  of  the  first,  a  second  curve  (fig.  283)  will  occur  which  will 
commence  at  the  highest  point  of  the  first  and  will  rise  as  high,  so 
that  the  sum  of  the  height  of  the  two  exactly  equals  twice  the 


Fig.  284. — Curve  of  tetanus,  obtained  from  the  gastrocnemius  of  a  frog,  where  the  shocks 
were  sent  in  from  an  induction  coil,  about  sixteen  times  a  second,  by  the  interruption 
of  the  primary  current  by  means  of  a  vibrating  spring-,  which  dipped  into  a  cup  of 
mercury,  and  "broke  the  primary  current  at  each  vibration. 

height  of  the  first.  If  a  third  and  a  fourth  shock  be  passed,  a 
similar  effect  will  ensue,  and  curves  one  above  the  other  will  be 
traced,  the  third  being  slightly  less  than  the  second,  and  the 
fourth  than  the  third.  If  the  shocks  be  repeated  at  short  inter- 
vals, however,  the  lever  after  a  time  ceases  to  rise  any  further, 
and  the  contraction  which  has  reached  its  maximum  is  main- 
tained (fig.  285),  and  the  lever  marks  a  straight  line  on  the  re- 
cording cylinder.      This  condition  is  called  tetanus  of  muscle.     The 


Fig.  285. — Curve  of  tetanus,  from  a  series  of  very  rapid  shocks  from  a  magnetic  interrupter. 

condition  of  "  an  ordinary  tetanic  muscular  movement  is  essen- 
tially a  vibratory  movement,  the  apparently  rigid  .  and  firm 
muscular  mass  is  really  the  subject  of  a  whole  series  of  vibra- 
tions,   a    series  namely   of   simple    spasms;    it    will    be    readily 


ohap.xv.]  MUSCLE  WOBK   AND   FATIGUE.  499 

understood    why  a    tetanised    muscle,   like   all    other    vibrating 
bodies,  gives  out  a  sound  "  (M.  Foster). 

If  the  stimuli  are  not  quite  so  rapidly  sent  in  the  line  of  maxi- 
mum contraction  becomes  somewhat  wavy,  indicating  a    slight 

tendency  of  the  muscle  to  relax  during  the  intervals  between  the 
stimuli  (fig.  284). 

Muscular  Work. — We  have  seen  (p.  153)  that  ivork  is  esti- 
mated by  multiplying  the  weight  raised,  by  the  height  through 
which  it  has  been  lifted.  It  has  been  found  that  in  order  to 
obtain  the  maximum  of  work,  a  muscle  must  be  moderately 
loaded:  if  the  weight  be  increased  beyond  a  certain  point,  the 
muscle  becomes  strained  and  raises  the  weight  through  so  small 
a  distance  that  less  work  is  accomplished.  If  the  load  is  still 
further  increased  the  muscle  is  completely  overtaxed,  cannot 
raise  the  weight,  and  consequently  does  no  work  at  all.  Practical 
illustrations  of  these  facts  must  be  familiar  to  every  one. 

The  power  of  a  muscle  is  usually  measured  by  the  maximum 
weight  which  it  will  support  without  stretching.  In  man  this  is 
readily  determined  by  weighting  the  body  to  such  an  extent  that 
it  can  no  longer  be  raised  on  tiptoe  :  thus  the  power  of  the  calf- 
muscles  is  determined  (Weber.) 

The  power  of  a  muscle  thus  estimated  depends  of  course  upon 
its  cross-section.  The  power  of  a  human  muscle  is  from  two 
to  three  times  as  great  as  a  frog's  muscle  of  the  same  sectional 
area. 

Fatigue  of  Muscle. — A  muscle  becomes  rapidly  exhausted 
from  repeated  stimulation,  and  the  more  rapidly,  the  more  quickly 
the  induction-shocks  succeed  each  other. 

This  is  indicated  by  the  diminished  height  of  contraction  in 
the  accompanying  diagrams  (fig,  286).  It  will  be  seen  that  the 
vertical  lines,  which  indicate  the  extent  of  the  muscular  contrac- 
tion, decrease  in  length  from  left  to  right.  The  line  a  b  drawn 
along  the  tops  of  these  lines  is  termed  the  "  fatigue  curve."  It  is 
usually  a  straight  line. 

In  the  first  diagram  the  effects  of  a  short  rest  are  shown  : 
there  is  a  pause  of  three  minutes,  and  when  the  muscle  is  again 
stimulated  it  contracts  up  to  a',  but  the  recovery  is  only  tempor- 
ary, and  the  fatigue  curve,  after  a  few  more  contractions,  becomes 
continuous  with  that  before  the  rest. 

k  k  2 


500  CAUSES  AXD   PHENOMENA  OF  MOTION.       [chap.  xy. 

In  the  second  diagram  is  represented  the  effect  of  a  stream  of 
oxygenated  blood.  Here  we  have  a  sudden  restoration  of  energy  : 
the  muscle  in  this  case  makes  an  entirely  fresh  start  from  a,  and 


Fig.  286. — Fatigue  muscle-curves.     (Ray  Lankester.) 

the  new  fatigue  curve  is  parallel  to,  and  never  coincides  with  the 

old  one. 

A  fatigued  muscle  has  a  much  longer  "  latent  period  "  than  a 

fresh  one.     The  slowness  with  which  muscles  respond  to  the  will 

when  fatigued  must  be  familiar  to  every  one. 

In   a  muscle   which    is    exhausted,   stimulation  only  causes    a 

contraction  producing  a  local   bulging  near  the  point   irritated. 

A  similar  effect  may  be  produced  in  a  fresh  muscle  by  a  sharp 

blow,  as  in  striking  the  biceps  smartly  with  the  edge  of  the  hand, 

when  a  hard  muscular  swelling  is  instantly  formed. 

Accompaniments  of  Muscular  Contraction. — (1.)  Heat  is 

developed  in  the  contraction  of  muscles.     Becquerel  and  Breschet 

found,  with  the  thermo- multiplier,  about  i°  Fahr.  of  heat  pro- 
duced by  each  forcible  contraction  of  a  man's  biceps  ;  and  when 
the  actions  were  long  continued,  the  temperature  of  the  muscle 
increased  20.  This  estimate  is  probably  high,  as  in  the  frog's 
muscle  a  considerable  contraction  has  been  found  to  produce 
an  elevation  of  temperature  equal  on  an  average  to  less  than  i°  C. 
It  is  not  known  whether  this  development  of  heat  is  due  to 
chemical   changes   ensuing  in  the  muscle,  or  to  the  friction  of  its 


chap,  xv.]  MUSCULAB   BOUND.  501 

fibres  vigorously  acting  :  in  either  case,  we  may  refer  to  it  a  part 

of  the  heat  developed  in  active  exercise  (p.  383). 

(2.)  Sound    is   said    to   be    produced   when    muscles  contract 

forcibly,  as  mentioned  above.  Wollaston  showed  that  this  sound 
might  be  easily  heard  by  placing  the  tip  of  the  little  finger  in 
the  ear,  and  then  making  some  muscles  contract,  as  those  of  the 
ball  of  the  thumb,  whose  sound  may  be  conducted  to  the  ear 
through  the  substance  of  the  hand  and  finger.  A  low  shaking 
or  rumbling  sound  is  heard,  the  height  and  loudness  of  the  note 
being  in  direct  proportion  to  the  force  and  quickness  of  the  mus- 
cular action,  and  to  the  number  of  fibres  that  act  together,  or,  as 
it  were,  in  time. 

(3.)  Changes  in  shape. — The  mode  of  contraction  in  the  trans- 
versely-striated muscular  tissue  has  been  much  disputed.  The 
most  probable  account  is,  that  the  contraction  is  effected  by  an 
approximation  of  the  constituent  parts  of  the  fibrils,  which,  at 
the  instant  of  contraction,  without  any  alteration  in  their  general 
direction,  become  closer,  flatter,  and  wider ;  a  condition  which  is 
rendered  evident  by  the  approximation  of  the  transverse  stria) 
seen  011  the  surface  of  the  fasciculus,  and  by  its  increased  breadth 
and  thickness.  The  appearance  of  the  zigzag  lines  into  which 
it  was  supposed  the  fibres  are  thrown  in  contraction,  is  due  to 
the  relaxation  of  a  fibre  which  has  been  recently  contracted,  and 
is  not  at  once  stretched  again  by  some  antagonist  fibre,  or 
whose  extremities  are  kept  close  together  by  the  contractions 
of  other  fibres.  The  contraction  is  therefore  a  simple,  and, 
according  to  Ed.  Weber,  an  uniform,  simultaneous,  and  steady 
shortening  of  each  fibre  and  its  contents.  What  each  fibril  or 
fibre  loses  in  length,  it  gains  in  thickness  :  the  contraction  is  a 
change  of  form  not  of  size ;  it  is,  therefore,  not  attended  with 
any  diminution  in  bulk,  from  condensation  of  the  tissue.  This 
has  been  proved  for  entire  muscles,  by  making  a  mass  of  muscle. 
or  many  fibres  together,  contract  in  a  vessel  full  of  water,  with 
which  a  fine,  perpendicular,  graduated  tube  communicates.  Any 
diminution  of  the  bulk  of  the  contracting  muscle  would  be 
attended  by  a  fall  of  fluid  in  the  tube  ;  but  when  the  experiment 
is  carefully  performed,  the  level  of  the  water  in  the  tube  remains 
the  same,  whether  the  muscle  be  contracted  or  not. 

In   thus   shortening,  muscles    appear    to    swell   up,   becoming 


502 


CAUSES  AXD   PHENOMENA   OF   MOTION.       [chap.  xv. 


rounder,  more  prominent,  harder,  and  apparently  tougher.  But 
this  hardness  of  muscle  in  the  state  of  contraction,  is  not  due  to 
increased  firmness  or  condensation  of  the  muscular  tissue,  but  to 
the  increased  tension  to  which  the  fibres,  as  well  as  their  tendons 
and  other  tissues,  are  subjected  from  the  resistance  ordinarily 
opposed  to  their  contraction.  "When  no  resistance  is  offered,  as 
when  a  muscle  is  cut  off  from  its  tendon,  not  only  is  no  hardness 
perceived  during  contraction,  but  the  muscular  tissue  is  even 
softer,  more  extensile,  and  less  elastic  than  in  its  ordinary  uncon- 
tracted  state. 

(4.)  Chemical  changes. — (a)  The  reaction  of  the  muscle  which 
is  normally  alkaline  or  neutral  becomes  decidedly  acid,  from  the 
development  of  sarcolactic  acid,  (b)  The  muscle  gives  out  car- 
bonic acid  gas  and  takes  up  oxygen,  the  amount  of  the  carbonic 
acid  given  out  not  appearing  to  be  entirely  dependent  upon  the 
oxygen  taken  in,  and  so  doubtless  in  part  arising  upon  some  other 
source.  (c)  Certain  imperfectly  understood  chemical  changes 
occur,  in  all  probability  connected  with  (a)  and  (b).  Glycogen  is 
diminished,  and  muscle  sugar  (inosite)  appears  ;  the  extractives 
are  increased. 

(5.)  Electrical  changes. — When  a  muscle  contracts  the  natural 
muscle  current  or  currents  of  rest  undergo  a  distinct  diminution, 
which  is  due  to  the  appearance  in  the  actively  contracting  muscle 
of  currents  in  an  opposite  direction  to  those  existing  in  the  muscle 
at  rest.  This  causes  a  temporary  deflection  of  the  needle  of  a 
galvanometer  in  a  direction  opposite  to  the  original  current,  and 
is  called  by  some  the  negative  variation  of  the  muscle  current,  and 
by  others  a  current  of  action. 

Conditions  of  Contraction. — (a)  The  irritability  of  muscle  is 
greatest   at   a   certain   mean   temperature  ;  (b)  after  a  number  of 


Fig.  287. — Muscle-curves  from  the  gastrocnemius  of  a  frog,  illustrating  effects  of  alterations 

in  temperature. 

contractions   a    muscle    gradually   becomes   exhausted ;    (c)    the 
activity  of  muscles  after  a  time  disappears  altogether  when  they 


ohap.xv.]    CONDITIONS   OP   KUSCULAB  CONTRACTION.  503 

ire  removed  from  t lie  body  or  the  arteries  are  tied;  (</)  oxygen 
is  used  up  in  muscular  contraction,  but  a  muscle  will  act  for 
■  time  '  or  a   gas  which  contains  no  oxygen  :    in   this 

f    course  using    up   the   oxygen    already   in 
<  Hermann). 

Response  to  Stimuli. — The  two  kinds  of  fibres,  the  striped 
ami  unstriped,  have  characteristic  differences  in  the  mode  in 
which  they  act  on  the  application  of  the  same  stimulus  ;  differ- 
ences which  may  be  ascribed  in  great  part  to  their  respective 
differences  of  structure,  but  to  some  degree,  possibly,  to  their 
ctive  modes  of  connection  with  the  nervous  system.  When 
irritation  is  applied  directly  to  a  muscle  with  striated  fibres,  or  to 
the  motor  nerve  supplying  it,  contraction  of  the  pait  irritated, 
and  of  that  only,  ensues  ;  and  this  contraction  is  instantaneous, 
and  ceases  on  the  instant  of  withdrawing  the  irritation.  But 
when  any  part  with  unstriped  muscular  fibres,  e.g.,  the  intestines 
or  bladder,  is  irritated,  the  subsequent  contraction  ensues  more 
slowly,  extends  beyond  the  part  irritated,  and,  with  alternating 
relaxation,  continues  for  some  time  after  the  withdrawal  of  the 
irritation.  The  difference  in  the  modes  of  contraction  of  the  two 
kinds  of  muscular  fibres  may  be  particularly  illustrated  by  the 
effects  of  the  electro-magnetic  stimulus.  The  rapidly  succeeding 
shocks  given  by  this  means  to  the  nerves  of  muscles  excite  in  all 
the  transversely-striated  muscles  a  fixed  state  of  tetanic  contrac- 
tion as  previously  described,  which  lasts  as  long  as  the  stimulus 
is  continued,  and  on  its  withdrawal  instantly  ceases ;  but  in  the 
muscles  with  smooth  fibres  they  excite,  if  any  movement,  only 
one  that  ensues  slowly,  is  comparatively  slight,  alternates  with 
rest,  and  continues  for  a  time  after  the  stimulus  is  withdrawn. 

In  their  mode  of  responding  to  these  stimuli,  all  the  skeletal 
muscles,  or  those  with  transverse  stria?,  are  alike  ;  but  among 
those  with  plain  or  unstriped  fibres  there  are  many  differences, — a 
fact   which   tends   to  confirm  the   opinion  that  their  peculiarity 

iids  as  well  on  their  connection  with  nerves  and  ganglia  as 
their  own  properties.  The  ureters  and  gall-bladder  are  the  parts 
excited  by  stimuli :  they  do  not  act  at  all  till  the  stimulus 
has  been  long  applied,  and  then  contract  feebly,  and  to  a  small 
extent.  The  contractions  of  the  caecum  and  stomach  are  quicker 
and    wider-spread  :    still    quicker   those    of   the    iris,   and   of  the 


504  CAUSES  AND   PHENOMENA   OF  MOTION.      [chap.  xv. 

urinary  bladder  if  it  be  not  too  full.  The  actions  of  the  small 
and  large  intestines,  of  the  vas  deferens,  and  pregnant  uterus,  are 
yet  more  vivid,  more  regular,  and  more  sustained ;  and  they 
require  no  more  stimulus  than  that  of  the  air  to  excite  them. 
The  heart,  on  account,  doubtless,  of  its  striated  muscle,  is  the 
quickest  and  most  vigorous  of  all  the  muscles  of  organic  life  in 
contracting  upon  irritation,  and  appears  in  this,  as  in  nearly  all 
other  respects,  to  be  the  connecting  member  of  the  two  classes  of 
muscles. 

All  the  muscles  retain  their  property  of  contracting  under  the 
influence  of  stimuli  applied  to  them  or  to  their  nerves  for  some 
time  after  death,  the  period  being  longer  in  cold-blooded  than 
in  warm-blooded  Vertebrata,  and  shorter  in  Birds  than  in 
Mammalia.  It  would  seem  as  if  the  more  active  the  respiratory 
process  in  the  living  animal,  the  shorter  is  the  time  of  duration 
of  the  irritability  in  the  muscles  after  death ;  and  this  is  con- 
firmed by  the  comparison  of  different  species  in  the  same  order 
of  Vertebrata.  But  the  period  during  which  this  irritability 
lasts,  is  not  the  same  in  all  persons,  nor  in  all  the  muscles  of  the 
same  persons.  In  a  man  it  ceases,  according  to  Nysten,  in  the 
following  order  : — first  in  the  left  ventricle,  then  in  the  intestines 
and  stomach,  the  urinary  bladder,  right  ventricle,  oesophagus, 
iris ;  then  in  the  voluntary  muscles  of  the  trunk,  lower  and 
upper  extremities  ;  lastly  in  the  right  and  left  auricle  of  the 
heart. 

III.  Rigor  Mortis. 

After  the  muscles  of  the  dead  body  have  lost  their  irritability 
or  capability  of  being  excited  to  contraction  by  the  application 
of  a  stimulus,  they  spontaneously  pass  into  a  state  of  contraction, 
apparently  identical  with  that  which  ensues  during  life.  It 
affects  all  the  muscles  of  the  body ;  and,  where  external  circum- 
stances do  not  prevent  it,  commonly  fixes  the  limbs  in  that  which 
is  their  natural  posture  of  equilibrium  or  rest.  Hence,  and  from 
the  simultaneous  contraction  of  all  the  muscles  of  the  trunk,  is 
produced  a  general  stiffening  of  the  body,  constituting  the  rigor 
mortis  or  post-mortem  rigidity. 

When  this  condition  has  set  in,  the  muscle  becomes  acid  in 
reaction  (due  to  sarco-lactic  acid),  and  gives  off  carbonic  acid  in 


map.  xv.  RIGOB  MORTIS.  -05 

slightly  diminished  :   the  muscular 
aed  and  opaque,  and  their  m 
firm.     If  -  on  much  more  rapidly  after  muscular  activity, 

and  is  hasi        I  by  warmth.     It  maybe  brought  on,  in  mm 
expoc  riment,  by  the  action  of  distilled  water  and  many 

acids,  also  by  freezing  and  thawing  again 

Cause.—  The  immediate  cause  of  rigor  Bet  igulation  of 

the  muscle  plasma  (Briicke,  Kiihne.  Norris).     We  may  distinguish 
three  main  stages.       1.    Gradual  coagulation.     (2.)  Contraction 

B  dated  muscle-clot  (myosin)  and  squeezing  out  of  mi 

scrum.     (3.)  Putrefaction.      After  the  first  stage,    restoration  is 

I    n  ble   through  the  circulation  of  arterial  blood    through    the 

.  and  even  when  the  second  .stage  lias  set  in,  vitality  may 

•   red  by  dissolving  the  coagulum  of  the  muscle  in  salt  solu- 

.    and  pase     _    arterial   Hood  through  its   vest  Is.       In   the 

third  stage  recvery  is  impossible. 

Order  of  Occurrence. — The  muscles  are  not  affected  sirnul- 
osly  by  postr-mortem    contraction.     It   affects  the  neck    and 
rjaw  first:  next,  the  upper  extremities,  extending  from  above 
downwards  :   and  lastly,   reaches  the  lower  limbs  ;  in  some  rare 
nst  .ices  only,  it  affects  the  lower  extremities  before,  or  simulta- 
neously with,  the    upper  extremities.     It   usually  ceases  in   the 
order  in  which  it   began  ;   first  at  the  head,   then  in  the   upper 
extremities,  and  lastly  in   the  lower  extremities.     It  never  com- 
mences earlier  than  ten  minutes,   and    never    later   than    seven 
hours,  after  death;  and   its  duration  is  greater  in  proportion  to 
the  lateness  of  its         —ion.     Heat  is  developed  during  the  pass 
of  a  muscular  fibre  into  the  condition  of  rigor  mortis. 

S  ice  rigidity  does  not  ensue  until  muscles  have  lost  the  capa- 
city "f  being  excited  by  external  stimuli,  it  follows  that  all 
circumstances  which  cause  a  speedy  exhaustion  of  muscular  irri- 
tability, induce  an  early  occurrence  of  the  rigidity,  while  condi- 
by  which  the  disappearance  of  the  irritability  is  delayed, 
are  succeeded  by  a  tardy  onset  «>f  this  rigidity.  Hence  its  speedy 
occurrence,  and  equally  speedy  departure  in  the  bodies  of  pt: 
exhausted  by  chronic  Ik  -  -  :  and  its  tardy  onset  and  long  con- 
tinuance after  sudden  death  from  acute  die  ses.  In  some  c 
of  sudden  death  from  lightning,  violent  injuries,  or  paroxyso 

■n,  rigor  mortis  has  been  .-aid   not  to  occur  at  all  ;  but  this 


506  CAUSES  AND   PHENOMENA   OF   MOTION.       [chap.  xv. 

is  not  always  the  case.  It  may,  indeed,  be  doubted  whether  there 
is  really  a  complete  absence  of  the  post-mortem  rigidity  in  any 
such  cases ;  for  the  experiments  of  Brown-Sequard  make  it  pro- 
bable that  the  rigidity  may  supervene  immediately  after  death, 
and  then  pass  away  with  such  rapidity  as  to  be  scarcely 
observable. 

Experiments. — Brown-Sequard  took  five  rabbits,  and  killed  them  by 
removing  their  hearts.  In  the  first,  rigidity  came  on  in  10  hours,  and  lasted 
192  hours  :  in  the  second,  which  was  feebly  electrified,  it  commenced  in  7 
hours,  and  lasted  144  ;  in  the  third,  which  was  more  strongly  electrified,  it 
came  on  in  two,  and  lasted  72  hours  ;  in  the  fourth  which  was  still 
more  strongly  electrified,  it  came  on  in  one  hour,  and  lasted  20  ;  while, 
in  the  last  rabbit,  which  was  submitted  to  a  powerful  electro-galvanic 
current,  the  rigidity  ensued  in  seven  minutes  after  death,  and  passed  away 
in  25  minutes.  From  this  it  appears  that  the  more  powerful  the  electric 
current,  the  sooner  does  the  rigidity  ensue,  and  the  shorter  is  its] duration  ; 
and  as  the  lightning  shock  is  so  much  more  powerful  than  any  ordinary 
electric  discharge,  the  rigidity  may  ensue  so  early  after  death,  and  pass 
away  so  rapidly  as  to  escape  detection.  The  influence  exercised  upon  the 
onset  and  duration  of  post-mortem  rigidity  by  causes  which  exhaust  the 
irritability  of  the  muscles,  was  well  illustrated  in  further  experiments  by 
the  same  physiologist,  in  which  he  found  that  the  rigor  mortis  ensued  far 
more  rapidly,  and  lasted  for  a  shorter  period  in  those  muscles  which  had  been 
powerfully  electrified  just  before  death  than  those  which  had  not  been  thus 
acted  upon. 

The  occurrence  of  rigor  mortis  is  not  prevented  by  the  previous 
existence  of  paralysis  in  a  part,  provided  the  paralysis  has  not 
been  attended  with  very  imperfect  nutrition  of  the  muscular 
tissue. 

The  rigidity  affects  the  involuntary  as  well  as  the  voluntary 
muscles,  whether  they  be  constructed  of  striped  or  unstriped 
fibres.  The  rigidity  of  involuntary  muscles  with  striped  fibres 
is  shown  in  the  contraction  of  the  heart  after  death.  The  con- 
traction of  the  muscles  with  unstriped  fibres  is  shown  by  an 
experiment  of  Valentin,  who  found  that  if  a  graduated  tube 
connected  with  a  portion  of  intestine  taken  from  a  recently-killed 
animal,  be  filled  with  water,  and  tied  at  the  opposite  end,  the 
water  will  in  a  few  hours  rise  to  a  considerable  height  in  the  tube, 
owino-  to  the  contraction  of  the  intestinal  walls.  It  is  still  better 
shown  in  the  arteries,  of  which  all  that  have  muscular  coats  con- 
tract after  death,  and  thus  present  the  roundness  and  cord-like 
feel  of  the  arteries  of  a  limb  lately  removed,  or  those  of  a  body 


I  HAP.   XV.] 


nI;l)KKS    (»F    LEY  Kits. 


507 


itly  dead.  Subsequently  they  relax,  as  do  all  the  other 
muscles,  and  Peel  Lax  and  flabby,  and  lie  as  if  flattened,  and  with 
their  walls  nearly  in  contact. 


Actions  of  the  Voluntary  Muscles. 

The  greater  part  of  the  voluntary  muscles  of  the  body  act  as 
sources  of  power  for  removing  levers, — the  latter  consisting  of  the 
various  bones  to  which  the  muscles  are  attached. 

f  the  three  orders  of  levers  in  the  Hitman  Body . — All  levers 
been  divided  into  three  kinds,  according  to  the  relative  position  of  the 
power,  the  weight  to  be  removed,  and  the  axis  of  motion  or  fulcrum.  In  a 
of  the  first  kind  the  power  is  at  one  extremity  of  the  lever,  the  weight 
at  the  other,  and  the  fulcrum  between  the  two.  If  the  initial  letters  only 
of  the  power,  weight,  and  fulcrum  be  used,  the  arrangement  will  stand 
thus  : — P.F.W.  A  poker,  as  ordinarily  used,  or  the  bar  in  fig.  288  may  be 
cited  as  an  example  of  this  variety  of  lever  ;  while,  as  an  instance  in  which 
the  bones  of  the  human  skeleton  are  used  as  a  lever  of  the  same  kind,  may 
l^e  mentioned  the  act  of  raising  the  body  from  the  stooping  posture  by 
means  of  the  hamstring  muscles  attached  to  the  tuberosity  of  the  ischium 
(fig.  288). 


Fig.  288. 

In  a  lever  of  the  second  kind,  the  arrangement  is  thus  : — P.W.F.  ;  and  this 
leverage  is  employed  in  the  act  of  raising  the  handles  of  a  wheelbarrow,  or 
in  stretching  an  elastic  band  as  in  fig.  289.  In  the  human  body  the  act  of 
opening  the  mouth  by  depressing  the  lower  jaw  is  an  example  of  the  same 
kind. — the  tension  of  the  muscles  which  close  the  jaw  representing  the 
weight  (fig.  289). 

In  a  lever  of  the  third  kind  the  arrangement  is — F.  1'.  W„  and  the  act  of 


;o8 


CAUSES  AXD   PHENOMENA   OF  MOTION.       [ciiAr.  xv. 


raising  a  pole,  as  in  fig.  290,  is  an  example.     In  the  human  body  there  are 
numerous  examples  of  the  employment  of  this  kind  of  leverage.     The  act  of 


w     T 


ElasticBBand 


_" 


Fig.  289. 

bending  the  fore-arm  may  be  mentioned  as  an  instance  (fig.  290).     The  act 
of  biting  is  another  example. 

At  the  ankle  we  have  examples  of  all  three  kinds  of  lever.  1st  kind- 
Extending  the  foot.  3rd  kind— Flexing  the  foot.  In  both  these  cases  the 
foot  represents  the  weight :  the  ankle  joint  the  fulcrum,  the  power  being 


Fig.  290. 


the  calf  muscles  in  the  first  case,  and  the  tibialis  anticus  in  the  second  case. 
2nd  kind — When  the  body  is  raised  on  tip-toe.  Here  the  ground  is  the 
fulcrum,  the  weight  of  the  body  acting  at  the  ankle  joint  the  weight,  and 
the  calf  muscles  the  power. 

In  the  human  body,  levers  are  most  frequently  used  at  a  disadvantage  as 
regards  power,  the  latter  being  sacrificed  for  the  sake  of  a  greater  range  of 
motion.  Thus  in  the  diagrams  of  the  first  and  third  kinds  it  is  evident  that 
the  power  is  so  close  to  the  fulcrum,  that  great  force  must  be  exercised  in 
order  to  produce  motion.  It  is  also  evident,  however,  from  the  same  dia- 
grams, that  by  the  closeness  of  the  power  to  the  fulcrum  a  great  range  of 
movement  can  be  obtained  by  means  of  a  comparatively  slight  shortening  of 
the  muscular  fibres. 

The  greater  number  of  the  more  important  muscular  actions 
of  the  human  body — those,  namely,  which  are  arranged  harmo- 
niously so   as  to  subserve  some  definite  purpose  or  other  in  the 


•  II  VI'.    XV.  j 


WALKING. 


509 


animal  economy — are  described  in  various  parts  of  this  work,  in 
the  sections  which  treat  of  the  physiology  of  the  processes  by 

which  these  muscular  actions  are  resisted  »>r  carried  out.  Tier! 
are,  however,  one  or  two  very  important  and  somewhat  compli 
cated  muscular  acts  which  may  be  best  described  in  this  place. 

Walking.— In  the  act  of  walking,  almost  every  voluntary  muscle  in  the 
body  is  brought  into  play,  cither  directly  for  purposes  of  progression,  or  in- 
directly for  the  proper  balancing  of  the  head  and  trunk.  The  muscles  of 
the  arms  arc  least  concerned  ;  but  even  these  are  for  the  most  part  instinctively 
in  action  also  to  some  extent. 

Among  the  chief  muscles  engaged  directly  in  the  act  of  walking  are  those 
of  the  calf,  which,  by  pulling  up  the  heel,  pull  up  also  the  astragalus,  and 
with  it.  of  course,  the  whole  body,  the  weight  of  wdrich  is  transmitted 
through  the  tibia  to  this  bone  (fig.  291).  When  starting  to  walk,  say  with 
the  left  leg,  this  raising  of  the  body  is  not  left  entirely  to  the  muscles  of  the 
left  calf,  but  the  trunk  is  thrown  forward  in  such  a  wray  that  it  would  fall 
prostrate  were  it  not  that  the  right  foot  is  brought  forward  and  planted  on 
the  ground  to  support  it.  Thus  the  muscles  of  the  left  calf  are  assisted  in 
their  action  by  those  muscles  on  the  front  of  the  trunk  and  legs  which,  by 
their  contraction,  pull  the  body  forwards  ;  and,  of  course,  if  the  trunk  form 


Fig.  291. 


a  slanting  line,  with  the  inclination  forwards,  it  is  plain  that  when  the 
heel  is  raised  by  the  calf -muscles,  the  whole  body  will  be  raised,  and  pushed 
obliquely  forwards  and  upwards.  The  successive  acts  in  taking  the  first 
step  in  walking  are  represented  in  fig.  291,  1,  2,  3. 

Now  it  is  evident  that  by  the  time  the  body  has  assumed  the  position 
No.  3,  it  is  time  that  the  right  leg  should  be  brought  forward  to  support  it 
and  prevent  it  from  falling  prostrate.  This  advance  of  the  other  leg  (in 
this  case  the  right)  is  effected  partly  by  its  mechanically  swinging  forwards, 
pendulum-wise,  and  partly  by  muscular  action  ;  the  muscles  used  being, — 
1st,  those  on  the  front  of  the  thigh,  which  bend  the  thigh  forwards  on  the 
pelvis,  especially  the  rectus  femoris,  with  the  psoas  and  the  iliacus  ;  znrfhj, 
the  hamstring  muscles,  which  slightly  bend  the  leg  on  the  thigh  ;  and  ^rdly, 
the  muscles  on  the  front  of  the  leg,  which  raise  the  front  of  the  foot  and 
toes,  and  so  prevent  the  latter  in  swinging  forwards  from  hitching  in  the 
ground. 


510  CAUSES   AND   PHENOMENA   OF  MOTION.       [chap.  xv. 

The  second  part  of  the  act  of  walking,  which  has  been  just  described,  is 
shown  in  the  diagram  (4,  fig.  291). 

When  the  right  foot  has  reached  the  ground  the  action  of  the  left  leg  has 
not  ceased.  The  calf-muscles  of  the  latter  continue  to  act,  and  by  pulling 
up  the  heel,  throw  the  body  still  more  forwards  over  the  right  leg,  now 
bearing  nearly  the  whole  weight,  until  it  is  time  that  in  its  turn  the  left  leg 
should  swing  forwards,  and  the  left  foot  be  planted  on  the  ground  to  prevent 
the  body  from  falling  prostrate.  As  at  first,  while  the  calf -muscles  of  one 
leg  and  foot  are  preparing,  so  to  speak,  to  push  the  body  forward  and  upward 
from  behind  by  raising  the  heel,  the  muscles  on  the  front  of  the  trunk  and 
of  the  same  leg  (and  of  the  other  leg,  except  when  it  is  swinging  forwards) 
are  helping  the  act  by  pulling  the  legs  and  trunk,  so  as  to  make  them  incline 
forward,  the  rotation  in  the  inclining  forwards  being  effected  mainly  at  the 
ankle  joint.  Two  main  kinds  of  leverage  are,  therefore,  employed  in  the 
act  of  walking,  and  if  this  idea  be  firmly  grasped,  the  detail  will  be  under- 
stood with  comparative  ease.  One  kind  of  leverage  employed  in  walking  is 
essentially  the  same  with  that  employed  in  pulling  forward  the  pole,  as  in 
fig.  290.  And  the  other,  less  exactly,  is  that  employed  in  raising  the  handles 
of  a  wheelbarrow.  Now.  supposing  the  lower  end  of  the  pole  to  be  placed 
in  the  barrow,  we  should  have  a  very  rough  and  inelegant,  but  not  altogether 
bad  representation  of  the  two  main  levers  employed  in  the  act  of  walking. 
The  body  is  pulled  forward  by  the  muscles  in  front,  much  in  the  same  way 
that  the  pole  might  be  by  the  force  applied  at  P.  (fig.  290),  while  the  raising 
of  the  heel  and  pushing  forwards  of  the  trunk  by  the  calf -muscles  is  roughly 
represented  on  raising  the  handles  of  the  barrow.  The  manner  in  which 
these  actions  are  performed  alternately  by  each  leg,  so  that  one  after  the 
other  is  swung  forwards  to  support  the  trunk,  which  is  at  the  same  time 
pushed  and  pulled  forwards  by  the  muscles  of  the  other,  may  be  gathered 
from  the  previous  description. 

There  is  one  more  thing  to  be  noticed  especially  in  the  act  of  walking. 
Inasmuch  as  the  body  is  being  constantly  supported  and  balanced  on  each 
leg  alternately,  and  therefore  on  only  one  at  the  same  moment,  it  is  evident 
that  there  must  be  some  provision  made  for  throwing  the  centre  of  gravity 
over  the  line  of  support  formed  by  the  bones  of  each  leg,  as,  in  its  turn,  it 
supports  the  weight  of  the  body.  This  may  be  done  in  various  ways,  and 
the  manner  in  which  it  is  effected  is  one  element  in  the  differences  which 
exist  in  the  walking  of  different  people.  Thus  it  may  be  done  by  an  in- 
stinctive slight  rotation  of  the  pelvis  on  the  head  of  each  femur  in  turn,  in 
such  a  manner  that  the  centre  of  gravity  of  the  body  shall  fall  over  the  foot 
of  this  side.  Thus  when  the  body  is  pushed  onwards  and  upwards  by  the 
raising,  say,  of  the  right  heel,  as  in  fig.  291,  3,  the  pelvis  is  instinctively  by 
various  muscles,  made  to  rotate  on  the  head  of  the  left  femur  at  the  ace- 
tabulum, to  the  left  side,  so  that  the  weight  may  fall  over  the  line  of  support 
formed  by  the  left  leg  at  the  time  that  the  right  leg  is  swinging  forwards, 
and  leaving  all  the  work  of  support  to  fall  on  its  fellow.  Such  a  "  rocking  " 
movement  of  the  trunk  and  pelvis,  however,  is  accompanied  by  a  movement 
of  the  whole  trunk  and  leg  over  the  foot  which  is  being  planted  on  the 
ground  (fig.  292)  ;  the  action  being  accompanied  with  a  compensatory  out- 
ward movement  at  the  hip,  more  easily  appreciated  by  looking  at  the  figure 
(in  which  this  movement  is  shown  exaggerated)  than  described. 

Thus  the  body  in  walking  is  continually  rising  and  swaying  alternately 
from  one  side  to  the  other,  as  its  centre  of  gravity  has  to  be  brought  alter- 


CHAP.  x\  .  | 


WALKING— LEAPING— RUNNING, 


511 


natclv  over  one  or  other  leg  :  and  the  curvatures  of  the  apine  are  altered  In 
correspondence  with  the  varying  position  of  the  weight  which  it  has  to 
support.  The  extent  to  which  the  body  is  raised  01  swayed  differs  much  in 
different  people. 

In  walking,  one  fool  or  the  other  is  always  on  the  ground.  The  act  of 
leaping  or  jumping  t  consists  in  bo  Budden  a  raising  of  the  heels  by  the  Bharp 
and  strong  contraction  of  the  calf-muscles,  that  the  body  is  jerked  off  the 


Fig.  292. 

ground.  At  the  same  time  the  effect  is  much  increased  by  first  bending  the 
thighs  on  the  pelvis,  and  the  legs  on  the  thighs,  and  then  suddenly  straighten- 
ing out  the  angles  thus  formed.  The  share  which  this  action  has  in  pro- 
ducing the  effect  may  be  easily  known  by  attempting  to  leap  in  the  upright 
posture,  with  the  legs  quite  straight. 

Running  is  performed  by  a  series  of  rapid  low  jumps  with  each  leg  alter- 
nately ;  so  that,  during  each  complete  muscular  act  concerned,  there  is  a 
moment  when  both  feet  are  off  the  ground. 

In  all  these  cases,  however,  the  description  of  the  manner  in  which  any 
given  effect  is  produced,  can  give  but  a  very  imperfect  idea  of  the  infinite 
number  of  combined  and  harmoniously  arranged  muscular  contractions  which 
are  necessary  for  even  the  simplest  acts  of  locomotion. 


Actions  of  the  Involuntary  Muscles. — The  involuntary 
muscles  arc  for  the  most  part  not  attached  to  bones  arranged  to 
act  as  levers,  but  enter  into  the  formation  of  such  hollow  parts  as 
require  a  diminution  of  their  calibre  by  muscular  action,  under 
particular  circumstances.     Examples  of  this  action  are  to  be  found 


512  CAUSES  AXD   PHENOMENA   OF   MOTION.      [chap.  xv. 

in  the   intestines,  urinary  bladder,  heart  and  blood-vessels,  gall- 
bladder, gland-ducts,  etc. 

The  difference  in  the  manner  of  contraction  of  the  striated  and 
non-striated  fibres  has  been  already  referred  to  (p.  503) ;  and  the 
peculiar  vermicular  or  peristaltic  action  of  the  latter  fibres  has 
been  described  at  p.  503. 

Source  of  Muscular  Action. 

It  was  formerly  supposed  that  each  act  of  contraction  on  the 
part  of  a  muscle  was  accompanied  by  a  correlative  waste  or 
destruction  of  its  own  substance ;  and  that  the  quantity  of  the 
nitrogenous  excreta,  especially  of  urea,  presumably  the  expression 
of  this  waste,  was  in  exact  proportion  to  the  amount  of  muscular 
work  performed.  It  has  been  found,  however,  both  that  the 
theory  itself  is  erroneous,  and  that  the  supposed  facts  on  which 
it  was  founded  do  not  exist. 

It  is  true  that  in  the  action  of  muscles,  as  of  all  other  parts, 
there  is  a  certain  destruction  of  tissue  or,  in  other  words,  a 
certain  '  wear  and  tear,'  which  may  be  represented  by  a  slight 
increase  in  the  quantity  of  urea  excreted  :  but  it  is  not  the 
correlative  expression  or  only  source  of  the  power  manifested. 
The  increase  in  the  amount  of  urea  which  is  excreted  after  mus- 
cular exertion  is  by  no  means  so  great  as  was  formerly  supposed  ; 
indeed,  it  is  very  slight.  And  as  there  is  no  reason  to  believe 
that  the  waste  of  muscle-substance  can  be  expressed,  with  un- 
important exceptions,  in  any  other  way  than  by  an  increased 
excretion  of  urea,  it  is  evident  that  we  must  look  elsewhere  than 
in  destruction  of  muscle,  for  the  source  of  muscular  action.  For, 
it  need  scarcely  be  said,  all  force  manifested  in  the  living  body 
must  be  the  correlative  expression  of  force  previously  latent  in 
the  food  eaten  or  the  tissue  formed ;  and  evidences  of  force 
expended  in  the  body  must  be  found  in  the  excreta.  If,  there- 
fore, the  nitrogenous  excreta,  represented  chiefly  by  urea,  are  not 
in  sufficient  quantity  to  account  for  the  work  done,  we  must 
look  to  the  non-nitrogenous  excreta  as  carbonic  acid  and  water, 
which,  presumably,  cannot  be  the  expression  of  wasted  muscle- 
substance. 

The  quantity  of  these  non-nitrogenous  excreta  is  undoubtedly 
increased  bv  active  muscular  efforts,  and  to  a  considerable  extent; 


OHAP.  XV.]  XKRVE  CURRENTS.  513 

and  whatever  may  be  the  Bource  <>f  the  water,  the  carbonic  acid, 
at  Least,  is  the  result  of  chemical  action  in  the  system,  and  espe- 
cially of  the  combustion  of  non-nitrogenous  food,  although,  doubt- 
of  nitrogenous  food  also.  We  are,  therefore,  driven  to  the 
conclusion, — that  the  substance  of  muscles  is  not  wasted  in  pro- 
portion to  the  work  they  perform  ;  and  that  the  con-nitrogenous 
as  well  as  tin'  nitrogenous  foods  may,  in  their  combustion,  afford 
the  requisite  conditions  for  muscular  action.  The  urgent  neces- 
sity for  nitrogenous  food,  especially  after  exercise,  is  probably  due 
more  to  the  need  of  nutrition  by  the  exhausted  muscles  and  other 
tissues  for  which,  of  course,  nitrogen  is  essential,  than  to  such 
food  being  superior  to  non-nitrogenous  substances  as  a  source  of 
muscular  power. 

The  electrical  condition  of  Nerves  is  so  closely  connected  with 
the  phenomena  of  muscular  contraction,  that  it  will  be  convenient 
to  consider  it  in  the  present  chapter. 

Electrical  currents  in  Nerves  — If  a  piece  of  nerve  be 
removed  from  the  body  and.  subjected  to  examination  in  a  way 
similar  to  that  adopted  in  the  case  of  muscle  which  has  been 
described  (p.  485),  electrical  currents  are  found  to  exist  which 
correspond  exactly  to  the  natural  muscle  currents,  and  which 
are  called  natural  nerve  currents  or  currents  of  rest,  according  as  one 
or  other  theory  of  their  existence  be  adopted,  as  in  the  case  with 
muscle.  One  point  (corresponding  to  the  equator)  on  the  surface 
being  positive  to  all  other  points  nearer  to  the  cut  ends,  and  the 
greatest  deflection  of  the  needle  of  the  galvanometer  taking  place 
when  one  electrode  is  applied  to  the  equator  and  the  other  to  the 
centre  of  either  cut  end.  As  in  the  case  of  muscle,  these  nerve- 
currents  undergo  a  negative  variation  when  the  nerve  is  stimu- 
lated, the  variation  being  momentary  and  in  the  opposite  direction 
to  the  natural  currents  ;  and  are  similarly  known  as  the  currents 
of  action.  The  currents  of  action  are  propagated  in  both  directions 
from  the  point  of  the  application  of  the  stimulus,  and  are  of 
m<  anentary  duration. 

Rheoscopic  Frog. — The  negative  variation  of  the  nerve  cur- 
rent may  be  demonstrated  by  means  of  the  following  experiment. 
— The  new  current  produced  by  stimulating  the  nerve  of  one  nerve- 
muscle  preparation  may  be  used  to  stimulate  the  nerve  of  a  second 
nerve-muscle  preparation.     The  foreleg  of  a  frog  with  the  nerve 

L  h 


5 14  CAUSES  AND  PHENOMENA   OF  MOTION.      [chap.  xv. 

going  to  the  gastrocnemius  cut  long  is  placed  upon  a  glass  plate, 
and  arranged  in  such  a  way  that  its  nerve  touches  in  two  places 
the  sciatic  nerve,  exposed  but  preserved  in  situ  in  the  thigh  of  the 
opposite  leg.  The  electrodes  from  an  induction  coil  are  placed  be- 
hind the  sciatic  nerve  of  the  second  preparation,  high  up.  On  stimu- 
lating the  nerve  with  a  single  induction  shock,  the  muscles  not 
only  of  the  same  leg  are  found  to  undergo  a  twitch,  but  also 
those  of  the  first  preparation,  although  this  is  not  near  the  elec- 
trodes, and  so  the  stimulation  cannot  be  due  to  an  escape  of  the 
current  into  the  first  nerve.  This  experiment  is  known  under 
the  name  "of  the  rheoscopic  frog. 

Nerve -stimuli. — Nerve-fibres  require  to  be  stimulated  before 
they  can  manifest  any  of  their  properties,  since  they  have  no 
power  of  themselves  of  generating  force  or  of  originating  impulses. 
The  stimuli  which  are  capable  of  exciting  nerves  to  action,  are, 
as  in  the  case  of  muscle,  very  diverse.  They  are  of  very  similar 
nature  in  each  case.  The  mechanical,  chemical,  thermal,  and  electric 
stimuli  which  may  be  used  in  the  one  case  are  also,  with  certain 
differences  in  the  methods  employed,  efficacious  in  the  other.  The 
chemical  stimuli  are  chiefly  these  :  withdrawal  of  water,  as  by 
drying,  strong  solutions  of  neutral  salts  of  potassium,  sodium,  &c., 
free  inorganic  acids,  except  phosphoric ;  some  organic  acids ;  ether, 
chloroform,  and  bile  salts.  The  electrical  stimuli  employed  are  the 
induction  and  continuous  currents  concerning  which  the  observa- 
tions in  reference  to  muscular  contraction  should  be  consulted 
p.  491  et  seq.  Weaker  electrical  stimuli  will  excite  nerve  than 
will  excite  muscle  ;  the  nerve  stimulus  appears  to  gain  strength  as 
it  descends,  and  a  weaker  stimulus  applied  far  from  the  muscle 
will  have  the  same  effect  as  a  somewhat  stronger  one  applied  to 
the  nerve  near  the  muscle. 

It  will  be  only  necessary  here  to  add  some  account  of  the  effect 
of  a  constant  electrical  current,  such  as  that  obtained  from 
Daniell's  battery,  upon  a  nerve.  This  effect  may  be  studied  with 
the  apparatus  described  before.  A  pair  of  electrodes  are  placed 
behind  the  nerve  of  the  nerve-muscle  preparation,  with  a  Du 
Bois  Eeymond's  key  arranged  for  short  circuiting  the  battery 
current,  in  such  a  way  that  when  the  key  is  opened  the  current 
is  sent  into  the  nerve,  and  when  closed  the  current  is  cut  off. 
It  will  be  found  that  with  a  current  of  moderate  strength  there 


CHAP,  xv.]  NERVE  CURRENTS.  5,5 

will  be  a  contraction  of  the  muscle  both  at  the  opening  and  at  the 
closing  of  the  key  (called  respectively  making  and  breaking  con- 
tractions), but  that  during  the  interval  between  these  two  1  vents 
the  muscle  remains  flaccid,  provided  the  battery  current  continues 
of  constant  intensity,  [f  the  current  be  a  very  weak  or  a  very 
strong  one  the  effect  is  not  quite  the  same;  one  or  other  of 
the  contractions  may  be  absent.  Which  of  these  contractions 
is  absent  depends  upon  another  circumstance,  viz.,  the  direc- 
tion of  the  current.  The  direction  of  the  current  may  be 
ascending  or  descending;  if  ascending,  the  anode  or  positive 
pole  is  nearer  the  muscle  than  the  kathode  or  negative  pole, 
and  the  current  to  return  to  the  battery  has  to  pass  up  the 
nerve,  if  descending,  the  position  of  the  electrodes  is  reversed. 
It  will  be  necessary  before  considering  this  question  further  to 
return  to  the  want  of  apparent  effect  of  the  constant  current 
during  the  interval  between  the  make  and  break  contraction  :  to 
all  appearance,  indeed,  no  effect  is  produced  at  all,  but  in 
reality  a  very  important  change  is  brought  about  in  the  nerve 
by  the  passage  of  the  current.  This  may  be  shown  in  two 
ways,  first  of  all  by  the  galvanometer.  If  a  piece  of  nerve  be 
taken,  and  if  at  either  end  an  arrangement  lie  made  to  test  the 
electrical  condition  of  the  nerve  by  means  of  a  pair  of  non-polari- 
sable  electrodes  connected  with  a  galvanometer,  while  to  the 
central  portion  a  pair  of  electrodes  connected  with  a  Daniell's 
battery  be  applied,  it  will  be  found  that  the  natural  nerve- 
currents  are  profoundly  altered  on  the  passage  of  the  constant 
current  (which  is  called  the  polarising  current)  in  the  neigh- 
bourhood. If  the  polarising  current  be  in  the  same  direction 
as  the  latter  the  natural  current  is  increased,  but  if  in  the 
direction  opposite  to  it,  the  natural  current  is  diminished.  This 
change,  produced  by  the  continual  passage  of  the  battery-current 
through  a  portion  of  the  nerve  is  to  be  distinguished  from  the 
negative  variation  of  the  natural  current  to  which  allusion  has 
been  already  made,  and  which  is  a  momentary  change  occurring 
on  the  sudden  application  of  the  stimulus.  The  condition  pro- 
duced in  a  nerve  by  the  passage  of  a  constant  current  is  known 
by  the  name  of  electroto 

The  other  way  of  showing  the  effect  of  the  same  polarising  cur- 
rent is  by  taking  a  nerve-muscle  preparation  and  applying  to  the 

L   L   2 


5i6 


CAUSES   AND   PHENOMENA   OF   MOTION.       [chap.  xy. 


nerve  a  pair  of  electrodes  from  an  induction  coil  whilst  at   a  point 
further  removed  from  the  muscle,   electrodes    from   a    Darnell's 
battery  are  arranged  with  a  key  for  short  circuiting  and  an  ap- 
paratus (reverser)  by  which  the  battery  current  may  be  reversed 
in  direction.     If  the  exact  point  be  ascertained  to  which  the  secon- 
dary coil  should  be  moved  from  the  primary  coil  in  order  that  a 
minimum  contraction  be  obtained  by  the  induction  shock,   and 
the  secondary  coil  be  removed  slightly  further  from  the  primary, 
the  induction  current  cannot  now  produce  a  contraction  ;  but  if  the 
polarising  current  be  sent  in  a  descending  direction,  that  is  to 
say,  with  the    kathode  nearest  the  other   electrodes,  the  induc- 
tion current,  which  was  before  insufficient,   will  prove  sufficient 
to  cause  a  contraction ;  whereby  indicating  that  with  a  descending 
current  the  irritability  of  the  nerve  is  increased.     By  means  of  a 
somewhat  similar  experiment  it  may  be  shown  that  an  ascending 
current   will  diminish   the  irritability  of  a  nerve.     Similarly,  if 
instead  of  applying  the  induction  electrodes  below  the  other  elec- 
trodes they  are  applied  between  them,  like  effects  are  demonstrated, 
indicating  that  in  the  neighbourhood  of  the  kathode  the  irritabi- 
lity of  the  nerve  is  increased  by  a  constant  current,  and  in  the 
neighbourhood  of  the  anode  diminished.     This  increase  in  irrita- 
bility is  called  katelectrotonus,  and  similarly  the  decrease  is  called 


Jt 


Fig.  293. — Diagram  illustrating  the  effects  of various  intensities  of the  polarising  currents.  n,n' 
nerve  ■  o,  anode ;  k,  kathode ;  the  curves  above  indicate  increase,  and  those  below 
decrease  of  u-ritabilitv,  and  when  the  current  is  small  the  increase  and  decrease  are 
both  small,  with  the  "neutral  point  near  a,  and  so  on  as  the  current  is  increased  in 
strength. 

anelectrotonus.  As  there  is  between  the  electrodes  both  an  increase 
and  a  decrease  of  irritability  on  the  passage  of  a  polarising  cur- 
rent it  must  be  evident  that  the  increase  must  shade  off  into  the 
decrease,  and  that  there  must  be  a  neutral  point  where  there  is 
neither  increase  nor  decrease  of  irritability.     The  position  of  this 


I  B  LP.  XV.  | 


NERVE   <  OB  RENTS. 


517 


neutral  point  is  found  to  vary  with  the  intensity  of  the  polarising 
current,  w  hen  the  current  is  weak  the  point  is  Dearer  the  anode,  when 
strong  nearer  the  kathode  (fig.  293).  When  a  constant  current 
passes  into  a  nerve,  therefore,  if  a  making  contraction  result,  it 
may  be  assumed  that  it  is  due  to  the  increased  irritability  pro- 
duced in  the  neighbourhood  of  the  kathode,  but  the  breaking 
contraction  must  be  produced  by  a  rise  in  irritability  from  a 
lowered  state  to  the  normal  in  the  neighbourhood  of  the  anode. 
The  contractions  produced  in  the  muscle  of  a  nerve-muscle  prepa 
ration  by  a  constant  current  have  been  arranged  in  a  table  which 
is  known  as  Pfliiger's  Law  of  Contractions.  It  is  really  only  a 
statement  as  to  when  a  contraction  may  be  expected  : — 


Descending  Current. 

Ascending  Current. 

Make.            Break. 

Make. 

Break. 

Weak  

Moderate    . . . 
Strong 

Yes. 
Yes. 
Yes. 

No. 
Yes. 
No. 

Yes. 
Yes. 

No. 

No. 

'"i  1  8. 

Yes. 

The  difficulty  in  this  table  is  chiefly  in  the  effect  of  a  weak 
current,  but  the  following  statement  will  explain  it.  The  increase  of 
irritability  at  the  kathode  is  more  potent  to  produce  a  contraction 
than  the  rise  of  irritability  from  a  lower  to  a  normal  condition  at 
the  anode.  With  weak  currents  the  only  effect  is  a  contraction  at 
the  make  of  both  ascending  and  descending  currents,  the  descend- 
ing current  being  more  potent  than  the  ascending  (and  with  still 
weaker  currents  is  the  only  one  which  produces  any  effect),  since 
the  kathode  is  near  the  muscle,  whereas  in  the  case  of  the  ascending- 
current  the  stimulus  has  to  pass  through  a  district  of  diminished 
irritability,  which  may  either  act  as  an  entire  block,  or  may 
diminish  slightly  the  contraction  which  follows.  As  the  polarising 
current  becomes  stronger,  recovery  from  anelectrotonus  is  able  to 
produce  a  contraction  as  well  as  katelectrotonus,  and  a  contrac- 
tion occurs  both  at  the  make  and  the  break  of  the  current. 
The  absence  of  contraction  with  a  very  strong  current  at  the 
break  of  the  ascending  current  may  be  explained  by  supposing 
that  the  region  of  fall  in  irritability  at  the  kathode  blocks  the 
stimulus  of  the  rise  in  irritability  at  the  anode. 


5 1 8  VOICE  AXD   SPEECH.  [chap.  xvi. 

Thus  we  have  seen  that  two  circumstances  influence  the  effect 
of  the  constant  current  upon  a  nerve,  viz.,  the  strength  and  direc- 
tion of  the  current.  It  is  also  necessary  that  the  stimulus  should 
be  applied  suddenly  and  not  gradually,  and  that  the  irritability  of 
the  nerve  be  normal,  and  not  increased  or  diminished.  Sometimes 
(when  the  nerve  is  specially  irritable  1)  instead  of  a  simple  con- 
traction a  tetanus  occurs  at  the  make  or  break  of  the  constant 
current.  This  is  especially  liable  to  occur  at  the  break  of  a  strong 
ascending  current  which  has  been  passing  for  some  time  into  the 
preparation  ;  this  is  called  Bitter  s  tetanus,  and  may  be  increased 
by  passing  a  current  in  an  opposite  direction  or  stopped  by  passing 
a  current  in  the  same  direction. 


CHAPTEE  XYI. 

THE    VOICE    AXD    SPEECH. 


In  nearly  all  air-breathing  vertebrate  animals  there  are  arrange- 
ments for  the  production  of  sound,  or  voice,  in  some  parts  of  the 
respiratory  apparatus.  In  many  animals,  the  sound  admits  of 
being  variously  modified  and  altered  during  and  after  its  produc- 
tion ;  and,  in  man,  one  such  modification  occurring  in  obedience 
to  dictates  of  the  cerebrum,  is  speech. 

Mode  of  Production  of  the  Human  Voice. 

It  has  been  proved  by  observations  on  living  subjects,  by 
means  of  the  laryngoscope,  as  well  as  by  experiments  on  the 
larynx  taken  from  the  dead  body,  that  the  sound  of  the  human 
voice  is  the  result  of  the  inferior  laryngeal  ligaments,  or  true 
vocal  cords  (A,  cv,  fig.  298)  which  bound  the  glottis,  being  thrown 
into  vibration  by  currents  of  expired  air  impelled  over  their  edges. 
Thus,  if  a  free  opening  exists  in  the  trachea,  the  sound  of  the 
voice  ceases,  but  returns  if  the  opening  is  closed.  An  opening 
into  the  air-passages  above  the  glottis,  on  the  contrary,  does  not 
prevent  the  voice  being  formed.     Injury  of  the  laryngeal  nerves 


OHAP.  xvi.] 


VOICE   AND   SPEECH. 


519 


move  the  vocal  cords  puts  an  end  to 

;   and  when  these  nerves  are  divided 


supplying  the  muscles  which 
the  formation  of  vocal  sounds 

on  both  sides,  the  lo^s  of 
voice  is  complete.  More- 
over, by  forcing  a  current 
of  air  through  the  larynx 
in  the  dead  subject,  clear 
vocal  sounds  are  produced, 
though  the  epiglottis,  the 
upper  ligaments  of  the 
larynx  or  false  vocal  cords, 
the  ventricles  between  them 
and  the  inferior  ligaments 
or  true  vocal  cords,  and 
the  upper  part  of  the  ary- 
tenoid cartilages,  be  all 
removed ;  provided  the 
true  vocal  cords  remain 
entire,  with  their  points  of 
attachment,  and  be  kept 
tense  and  so  approximated 
that  the  fissure  of  the  glot- 
tis may  be  narrow. 

The  vocal  ligaments  or 
cords,  therefore,  may  be  re- 
garded as  the  proper  organs 
of  the  mere  voice :  the 
modifications  of  the  voice 
being  effected  by  other 
parts — tongue,  teeth,  lips, 
etc.,  as  well  as  by  them. 
The  structure  of  the  vocal 
cords  is  adapted  to  enable 
them  to  vibrate  like  tense 
membranes,  for  they  are 
essentially     composed      of 

elastic  tissue  ;  and  they  are  so  attached  to  the  cartilaginous  parts 
of  the  larynx  that  their  position  and  tension  can  be  variously 
altered  by  the  contraction  of  the  muscles  which  act  on  these  parts. 


|S 


Fig".  294. —  Outline  showing  the  general  form  of  the 
In  rytiXf  trachea,  and  bronchi,  as  seen  from  L 
h,  the  great  cornu  of  the  hyoid  bone ;  e,  epi- 
glottis ;  t,  superior,  and  t',  inferior  cornu  of 
the  .thyroid  cartilage  ;  c,  middle  of  the  cricoid 
cartilage;  tr,  the  trachea,  showing  sixteen 
cartilaginous  rings ;  b,  the  right,  and  V ,  the 
left  bronchus,     x  A.     (Allen  Thomson.) 


520 


VOICE  AXD   SPEECH. 


[CHAP.  XVI. 


The  Larynx. — The  larynx,  or  organ  of  voice,  consists  essen- 
tially of  the  two  vocal  cords,   which   are  so  attached   to  certain 

cartilages,  and  so  under 
the  control  of  certain  mus- 
cles, that  they  can  be  made 
the  means  not  only  of 
closing  the  aperture  of  the 
larynx  (rima  glottidis),  of 
which  they  are  the  lateral 
boundaries,  against  the  en- 
trance and  exit  of  air  to  or 
from  the  lungs,  but  also 
can  be  stretched  or  relaxed, 
shortened  or  lengthened, 
in  accordance  with  the  con- 
ditions that  may  be  neces- 
sary for  the  air  in  passing 
over  them,  to  set  them 
vibrating  and  produce  vari- 
ous sounds.  Their  action 
in  respiration  has  been  al- 
ready referred  to  (p.  234). 
In  the  present  chapter  the 
sound  produced  by  the 
vibration  of  the  vocal  cords 
is  the  only  part  of  their 
function  with  which  we 
have  to  deal. 


Fig.  295. —  Outline  showing  the  general  form  of  the 
larynx,  trachea,  and  brow 

ft,  great  cornu  of  the  hyoid  bone  :  t,  superior, 
and  t',  the  inferior  cornu  of  the  thyroid  carti- 
lage ;  e,  the  epiglottis  ;  ",  points  to  the  back 
of  both  the  arytenoid  cartilages,  which  are 
surmounted  by"  the  cornicula ;  c,  the  middle 
ridge  on  the  back  of  the  cricoid  cartilage ; 
t  r,  the  posterior  membranous  part  of  the 
trachea  ;  b,  V,  right  and  left  bronchi.  X  h. 
(Allen  Thomson.) 


Anatomy  of  the  Larynx-  — 
The  principal  parts  entering 
into  the  formation  of  the  larynx 
(figs.  294  and  295)  are — (7)  the 
thyroid  cartilage  ;  (js)  the  cri- 
coid cartilage  ;  (a~)  the  two 
arytenoid  cartilages  ;  and  the 
two  true  vocal  cords  (A.  cv,  fig. 
298).  The  epiglottis  (fig.  29S  e), 
has  but  little  to  do  with  the 


voice,  and  is  chiefly  useful  in 
falling  down  as  a  "lid"  over  the  upper  part  of  the  larynx,  to  help  in 
preventing  the  entrance  of  food  and  drink  in  deglutition.  It  also  guides 
mucus    or    other   fluids  in    small    amount   from   the    mouth    around    the 


OHAP.  xvi.] 


THE    l.AKY.W. 


521 


sides  of  the  upper  opening  of  the  glottis  into  the  pharynx  and  oesophagus: 
thus  preventing  them  from  entering  the  larynx.  The  raise  rocal  cords 
{evt,  fig.  298),  and  the  ventricle  of  the  larynx,  which  is  a  space  bi 
t  Ik-  Ealse  and  the  true  cord  of  either  side,  aeed  !>'•  here  only  referred  to. 
Cartilages. — The  thyroid  cartilage  (fig.  206.  1  to  4)  does  nol  form  a  corn- 
ring  around  the  larynx,  but  only  covers  the  front  portion.  The 
cricoid  cartilage   ( li.-r-  296,  5,  6),  on  the  other 

hand,  is  a  complete   rin<_r  ;    the   l>a<-k    pari    of 

the  ring  being  much  broader  than  the  front. 
On  the  top  of  this  broad  portion  of  the  cricoid 
are  the  arytenoid  cartilages  (fig.  298  a)  the 
connection  between  the  crioid  below  and 
arytenoid  cartilages  above  being  a  joint 
with  synovial  membrane  and  ligaments,  the 
latter  permitting  tolerably  free  motion  be- 
tween them.  But  although  the  arytenoid 
cartilages  can  move  on  the  cricoid,  they  of 
course  accompany  the  latter  in  all  their 
movements,  just  as  the  head  may  nod  or  turn 
on  the  top  of  the  spinal  column,  but  must 
accompany  it  in  all  its  movements  as  a  whole. 

Ligaments. — The  thyroid  cartilage  is  also 
connected  with  the  cricoid,  not  only  by  liga- 
ments, but  by  two  joints  with  synovial  mem- 
brane (t',  figs.  294  and  295) ;  the  lower  comma 
of  the  thyroid  clasping,  or  nipping,  as  it  were, 
the  cricoid  between  them,  but  not  so  tightly 
but  that  the  thyroid  can  revolve,  within  a 
certain  range,  around  an  axis  passing  trans- 
versely through  the  two  joints  at  which  the 
cricoid  is  clasped.  The  vocal  cords  are  at- 
tached (behind)  to  the  front  portion  of  the 
base  of  the  arytenoid  cartilages,  and  (in 
front)  to  the  re-entering  angle  at  the  back 
]  >art  of  the  thyroid  ;  it  is  evident,  therefore, 
that  all  movements  of  either  of  these  carti- 
lages must  produce  an  effect  on  them  of  some  kind  or  other.  Inasmuch* 
too,  as  the  arytenoid  cartilages  rest  on  the  top  of  the  back  portion  of  the 
cricoid  cartilage  (a,  fig.  29S),  and  are  connected  with  it  by  capsular  and 
other  ligaments,  all  movements  of  the  cricoid  cartilage  must  move  the 
arytenoid  cartilages,  and  also  produce  an  effect  on  the  vocal  cords. 

Intrinsic  Muscles. — The  so-called  intrinsic  muscles  of  the  larynx,  or 
th>  ee  which,  in  their  action,  have  a  direct  action  on  the  vocal  cords,  are  nine 
in  number — four  pairs,  and  a  single  muscle  ;  namely,  two  erico-thyroid 
muscles,  two  thyro-arytenoid,  two  posterior  erico-arytenoid,  two  lateral 
crico-arytenoid,  and  one  arytenoid  muscle.  Their  actions  are  as  follows  : — 
When  the  crico-thyroid  muscles  (10,  fig.  297)  contract,  they  rotate  the 
cricoid  on  the  thyroid  cartilage  in  such  a  manner  that  the  upper  and  back 
part  of  the  former,  and  of  necessity  the  arytenoid  cartilages  on  the  top  of  it, 
are  tipped  backwards,  while  the  thyroid  is  inclined  forward  :  and  thus,  of 
course,  the  vocal  cords  being  attached  in  front  to  one,  and  behind  to  the 
other,  are  "  put  on  the  stretch." 


Fig.  296.— Cartilages  of  the  larynx 
si  ■  n  from  before,  i  to  4,  thyroid 
cartilage ;  1,  vertical  ridge  or 
poraum  Adami  ;  2,  right  ala  ;  .;, 
superior,  and  4,  inferior  cornu  of 
the  right  side  ;  5,  6,  cricoid  carti- 
lage ;  5,  inside  of  the  posterior 
part  ;  6,  anterior  narrow  part  of 
the  ring  ;  7,  arytenoid  cartilages. 
x  f. 


522 


VOICE  AND    SPEECH.  [chap.  xvi. 


The  thyro-arytenoid  muscles  (7.  fig.  300)  on  the  other  hand,  have  an  oppo- 
site action. — pulling  the  thyroid  backwards,  and  the  arytenoid  and  upper  and 
back  part  of.  the  cricoid  cartilages  forwards,  and  thus  relaxing  the  vocal 

cords. 

The  crico-arytenoidti  pogtiei  muscles  (fig.  299.  V)  dilate  the  glottis,  and 

separate  the  vocal  cords,  the  one  from  the  other,  by  an  action  on  the  ary- 
tenoid cartilage  which  will  be  plain  on 
reference  to  B'  and  C,  (fig.  298).  By 
their  contraction  they  tend  to  pull  toge- 
ther the  outer  angles  of  the  arytenoid 
cartilages  in  such  a  fashion  as  to  rotate 
/  the  latter  at  their  joint  with  the  cricoid, 

and  of  course  to  throw  asunder  their  an- 
terior angles  to  which  the  vocal  cords 
are  attached. 

\  These  posterior  crico-arytenoid  muscles 

/  ^  are  opposed  by  the  eryeo-arytenoidei 
lateral  a.  which,  pulling  in  the  opposite 
direction  from  the  other  side  of  the  axis 
of  rotation,  have  of  course  exactly  the 
opposite  effect,  and  close  the  glottis  (fig. 
300,  4  and  5). 

The  aperture  of  the  glottis  can  be  also 
contracted  by  the  arytenoid  muscle 
(.-.  fig.  299  and  6,  fig.  300),  which,  in  its 
contraction,  pulls  together  the  upper 
parts  of  the  arytenoid  cartilages  between 
which  it  extends. 

Fig.  297.— L  ■  of  exterior  of         Nerve  Supply.— In  the  performance  of 

the  larynx.    8.  thyroid  cartilage :  9,      the  functions  of  the  lamix  the  sensory 

2SL;C£'£&M&HS     ®™"**»  of  the  Pneumo^mc  supply 
12,  first  rings  of  trachea.    (Willis.)        that  acute  sensibility  by  which  the  glottis 

is  guarded  against  the  ingress  of  foreign 
bodies,  or  of  irrespirable  gases.  The  contact  of  these  stimulates  the  filaments 
of  the  superior  laryngeal  branch  of  the  pneumogastric  :  and  the  impression 
conveved  to  the  medulla  oblongata,  whether  it  produce  sensation  or  not,  is 
reflected  to  the  filaments  of  the  recurrent  or  inferior  laryngeal  branch,  and 
excites  contraction  of  the  muscles  that  close  the  glottis.  Botli  these 
branches  of  pneumogastric  co-operate  also  in  the  production  and  regulation 
of  the  voice  ;  the  inferior  laryngeal  determining  the  contraction  of  the 
muscles  that  vary  the  tension  of  the  vocal  cords,  and  the  superior  laryngeal 
conveving  to  the  mind  the  sensation  of  the  state  of  these  muscles  necessary 
for  their  continuous  guidance.  And  both  the  branches  co-operate  in  the 
actions  of  the  larynx  in  the  ordinary  slight  dilatation  and  contraction  of  the 
elottis  in  the  acts  of  expiration  and  inspiration,  and  more  evidently  in 
those  of  coughing  and  other  forcible  respiratory  movements. 

Movements  of  Vocal  Cords. — The  placing  of  the  vocal 
cords  in  a  position  parallel  one  with  the  other,  is  effected  by  a 
combined  action  of  the  various  little  muscles  which  act  on  them 
the  thvro-arytenoidei  having,  without  much  reason,  the  credit 


CHAP,  xvi.]  MOVEMENTS   OF  VOCAL  CORDS.  523 

of  taking  the  largest  share  in  the  production  of  this  effect  Fig. 
298  is  intended  to  show  the  various  positions  of  the  vocal  cord 
under  different  circumstances.      Thus,  in  ordinary  tranquil  breath- 


Fig.  298. — Three  laryngoscopic  views  of  the  superior  aperture  of  the  larynx  and  surrounding 
to.  A,  the  glottis  during  the  emission  of  a  high  note  in  singing ;  B,  in  easy  and. 
quiet  inhalation  of  air  ;  C,  in  the  state  of  widest  possible  dilatation,  as  in  inhaling  a 
very  deep  breath.  The  diagrams  A',  B',  and  C,  have  been  added  to  Czermak's  figures, 
to  .-how  in  horizontal  sections  of  the  glottis  the  position  of  the  vocal  ligaments  and 
arytenoid  cartilages  in  the  three  several  states  represented  in  the  other  figures.  In  all 
the  figures,  so  far  as  marked,  the  letters  indicate  the  parts  as  follows,  viz.  :  /,  the  base 
of  the  tongue  ;  e,  the  upper  free  part  of  the  epiglottis  ;  >■' ,  the  tubercle  or  cushion  of 
the  epiglottis  ;  ph ,  part  of  the  anterior  wall  of  the  pharynx  behind  the  larynx  ;  in  the 
margin  of  the  aryteno-epiglottidean  fold  w,  the  swelling  of  the  membrane  caused  by 
the  cartilages  of  \Vrisberg ;  s,  that  of  the  cartilages  of  Santorini  ;  ",  the  tip  or  summit 
of  the  arytenoid  cartilages ;  c  v,  the  true  vocal  cords  or  lips  of  the  rima  glottidis  ; 
cvs,  the  superior  or  false  vocal  cords  ;  between  them  the  ventricle  of  the  larynx  ;  in 
C,  tr  is  placed  on  the  anterior  wall  of  the  receding  trachea,  and  b  indicates  the  com- 
mencement of  the  two  bronchi  beyond  the  bifurcation  which  may  be  brought  into 
view  in  this  state  of  extreme  dilatation.     (Czermak.)     (From  Quain's  Anatomy.) 

ing,  the  opening  of  the  glottis  is  wide  and  triangular  (b)  becoming 
a  little  wider  at  each  inspiration,  and  a  little  narrower  at  each 
expiration.  On  making  a  rapid  and  deep  inspiration  the  opening 
of  the  glottis  is  widely  dilated  (as  in  c),  and  somewhat  lozenge- 
shaped.     At  the  moment  of  the  emission  of  sound,  it  is  narrowed, 


524 


VOICE  AXD   SPEECH. 


[tHAP.  XVI. 


the  margins  of  the  arytenoid  cartilages  being  brought  into  contact 
and  the  edges  of  the  vocal  cords  approximated  and  made  parallel, 
at  the  same  time  that  their  tension  is  much  increased.  The 
higher  the  note  produced,  the  tenser  do  the  cords  become  (fig. 
29S,  a)  ;  and  the  range  of  a  voice  depends,  of  course,  in  the  main, 


Fig.  2:     -  of  the  larynx  and  part  of  the  trachea  from  beh ind.  -with  the  muscles  dis- 

sected ;  h.  the  body  of  the  hyoid  bone  ;  e,  epiglottis  :  t,  the  posterior  borders  of  the 
thyroid  cartilage  :  c,  the  median  ridge  of  the  cricoid  ;  o,  upper  part  of  the  arytenoid; 
.-.placed  on  one  of  the  oblique  fasciculi  of  the  arytenoid  muscle;  b.  left  posterior 
erico-arytenoid  muscle ;  ends  of  the  incomplete  cartilaginous  rings  of  the  trachea  : 
7.  fibrous  membrane  crossing  the  back  of  the  trachea ;  u,  muscular  fibres  exposed  in  a 
part  ;from  Quain's  Anatomy). 


on  the  extent  to  which  the  degree  of  tension  of  the  vocal  cords 
can  be  thus  altered.  In  the  production  of  a  high  note,  the  vocal 
cords  are  brought  well  within  sight,  so  as  to  be  plainly  visible 
with  the  help  of  the  laryngoscope.  In  the  utterance  of  grave 
tones,  on  the  other  hand,  the  epiglottis  is  depressed  and  brought 
over  them,  and  the  arytenoid  cartilages  look  as  if  they  were  trying 
to  hide  themselves  under  it  (fig.  301).  The  epiglottis,  by  being 
somewhat  pressed  down  so  as  to  cover  the  superior  cavity  of  the 
larynx,  serves  to  render  the  notes  deeper  in  tone,  and  at  the  same 


CHAP.  \'\  l.  ] 


MOVEMENTS  OF  VOCAL  CORDS. 


525 


time  somewhat  duller,  just  as  covering  the  end  of  a  short  tube 
placed   iu  front  of  caoutchouc  tongues  lowers  the  tone.     In  no 
other    respect  does  the  epiglottis 
appear  to  have  any  effect  in  modi- 
fying the  vocal  sounds. 

The  degree  of  approximation  of 
the  vocal  cords  also  usually  corre- 
sponds with  the  height  of  the  note 
produced  ;  but  probably  not  always, 
for  the  width  of  the  aperture  has 
no  essential  influence  on  the  height 
of  the  note,  as  long  as  the  vocal 
cords  have  the  same  tension  :  only 
with  a  wide  aperture,  the  tone  is 
more  difficult  to  produce,  and  is 
less  perfect,  the  rushing  of  the  air 
through  the  aperture  being  heard 
at  the  same  time. 

No  true  vocal  sound  is  produced 
at  the  posterior  part  of  the  aper- 
ture of  the  glottis,  that,  viz.,  which 

is  formed  by  the  space  between  the  arytenoid  cartilages.     For,  as 
Mailer's  experiments  showed,  if  the  arytenoid  cartilages  be   ap- 
proximated in  such  a  manner  that  ., 
their  anterior  processes  touch  each 
other,   but   yet   leave  an  opening 
behind  them  as  well  as  in  front, 
no  second  vocal  tone  is  produced 
by  the  passage  of  the  air  through 
the  posterior  opening,  but  merely 
a  rustling  or  bubbling  sound  ;  and 
the  height    or  pitch  of  the   note 
produced  is  the  same  whether  the 
posterior   part   of   the    glottis   be 
open  or  not,  provided  the  vocal  cords  maintain  the  same  degree 
of  tension. 


Fig.  300. —  View  of  the  anterior  of  la  ryn  K 
from  above.  1,  aperture  of  glottis  ; 
2 ,  arytenoid  cartilages ;  3 ,  vocal  cords ; 

4,  posterior  crico-arytenoid  muscles  ; 

5,  lateral  crico-arytenoid  muscle  of 
right  side,  that  of  leftside  removed 

6,  arytenoid  muscle ;  7,  thyro-ary- 
tenoid  muscle  of  left  side,' that  of 
right  side  removed  ;  8,  thyroid  carti- 
lage; 9,  cricoid  cartilage;  13,  pos- 
terior crico  -  arytenoid  ligament. 
(Willis.) 


K/ih.      " 


Fig.  301. — View  of  the  upper  part  of  the 
larynx  as  seen  by  means  of  the  laryn- 
goscope during  the  utterance  of  a 
grave  note,  e,  epiglottis  ;  s,  tuber- 
cles of  the  cartilages  of  Santorini ; 
a,  arytenoid  cartilages ;  2,  base  of 
the  tongue  ;  hph,  the  posterior  wall 
of  the  pharynx  (Czermak). 


526  VOICE  AXD   SPEECH.  [chap.  xvi. 

Application  of  the  Voice  in  Singing  and  Speaking. 

Varieties  of  Vocal  Sounds. — The  notes  of  the  voice  thus 
produced  may  observe  three  different  kinds  of  sequence.  Thefrst 
is  the  monotonous,  in  which  the  notes  have  nearly  all  the  same 
pitch  as  in  ordinary  speaking;  the  variety  of  the  sounds  of  speech 
being  due  to  articulation  in  the  mouth.  In  speaking,  however, 
occasional  syllables  generally  receive  a  higher  intonation  for  the 
sake  of  accent.  The  second  mpde  of  sequence  is  the  successive 
transition  from  high  to  low  notes,  and  vice  versa,  without  intervals  ; 
such  as  is  heard  in  the  sounds,  which,  as  expressions  of  passion, 
accompany  crying  in  men,  and  in  the  howling  and  whining  of  dogs. 
The  third  mode  of  sequence  of  the  vocal  sounds  is  the  musical,  in 
which  each  sound  has  a  determinate  number  of  vibrations,  and 
the  numbers  of  the  vibrations  in  the  successive  sounds  have 
the  same  relative  proportions  that  characterise  the  notes  of  the 
musical  scale. 

Compass  of  the  Voice. — In  different  individuals  this  compre- 
hends one,  two,  or  three  octaves.  In  singers — that  is,  in  persons 
apt  for  singing — it  extends  to  two  or  three  octaves.  But  the  male 
and  female  voices  commence  and  end  at  different  points  of  the 
musical  scale.  The  lowest  note  of  the  female  voice  is  about  an 
octave  higher  than  the  lowest  of  the  male  voice  ;  the  highest  note 
of  the  female  voice  about  an  octave  higher  than  the  highest  of  the 
male.  The  compass  of  the  male  and  female  voices  taken  together, 
or  the  entire  scale  of  the  human  voice,  includes  about  four  octaves. 
The  principal  difference  between  the  male  and  female  voice  is, 
therefore,  in  their  pitch  ;  but  they  are  also  distinguished  by  their 
tone, — the  male  voice  is  not  so  soft. 

Pitch  and  Timbre.  —  The  voice  presents  other  varieties 
besides  that  of  male  and  female ;  there  are  two  kinds  of  male 
voice,  technically  called  the  bass  and  tenor,  and  two  kinds  of 
female  voice,  the  contralto  and  soprano,  all  differing  from  each 
other  in  tone.  The  bass  voice  usually  reaches  lower  than  the 
tenor,  and  its  strength  lies  in  the  low  notes  ;  while  the  tenor 
voice  extends  higher  than  the  bass.  The  contralto  voice  has 
generally  lower  notes  than  the  soprano,  and  is  strongest  in  the 
lower  notes  of  the  female  voice  ;  while  the  soprano  voice  reaches 
higher  in  the  scale.     But  the  difference  of  compass,  and  of  power 


.hap.  xvi.]  VARIETIES  OF  VOICES.  527 

in  different  parts  of  the  scale,  is  not  the  essential  distinction 
between  the  different  voices;  for  bass  singers  can  sometimes  go 
very  high,  and  the  contralto  frequently  Bings  the  high  notes  like 
soprano  singers.  The  essentia]  difference  between  the  bass  and 
tenor  voices,  and  between  the  contralto  and  soprano,  consists  in 
their  tone  or  "  timbre,"  which  distinguishes  them  even  when  they 
are  singing  the  same  note.  The  qualities  of  the  barytone  and 
mezzo-soprano  voices  are  less  marked  ;  the  barytone  being  inter- 
mediate, between  the  bass  and  tenor,  the  mezzo-soprano  between 
the  contralto  and  soprano.  They  have  also  a  middle  position  as 
to  pitch  in  the  scale  of  the  male  and  female  voices. 

The  different  pitch  of  the  male  and  the  female  voices  depends 
on  the  different  length  of  the  vocal  cords  in  the  two  sexes ;  their 
relative  length  in  men  and  women  being  as  three  to  two.  The 
difference  of  the  two  voices  in  tone  or  "  timbre,"  is  owing  to  the 
different  nature  and  form  of  the  resounding  walls,  which  in  the 
male  larynx  are  much  more  extensive,  and  form  a  more  acute 
angle  anteriorly.  The  different  qualities  of  the  tenor  and  bass, 
and  of  the  alto  and  soprano  voices,  probably  depend  on  some 
peculiarities  of  the  ligaments,  and  the  membranous  and  cartila- 
ginous parietes  of  the  laryngeal  cavity,  which  are  not  at  present 
understood,  but  of  which  wre  may  form  some  idea,  by  recollecting 
that  musical  instruments  made  of  different  materials,  e.g.,  metallic 
and  gut-strings,  may  be  tuned  to  the  same  note,  but  that  each 
will  give  it  with  a  peculiar  tone  or  "  timbre." 

Varieties  of  Voices. — The  larynx  of  boys  resembles  the 
female  larynx ;  their  vocal  cords  before  puberty  have  not  two- 
thirds  the  length  which  they  acquire  at  that  period ;  and  the 
angle  of  their  thyroid  cartilage  is  as  little  prominent  as  in  the 
female  larynx.  Boys'  voices  are  alto  and  soprano,  resembling  in 
pitch  those  of  women,  but  louder,  and  differing  somewhat  from 
them  in  tone.  But,  after  the  larynx  has  undergone  the  change 
produced  during  the  period  of  development  at  puberty,  the  boy's 
voice  becomes  bass  or  tenor.  While  the  change  of  form  is  taking 
place,  the  voice  is  said  to  "crack;"  it  becomes  imperfect,  frequently 
hoarse  and  crowing,  and  is  unfitted  for  singing  until  the  new  tones 
are  brought  under  command  by  practice.  In  eunuchs,  who  have 
been  deprived  of  the  testes  before  puberty,  the  voice  does  not 
undergo  this  change.     The  voice  of  most  old  people  is  deficient  in 


528  VOICE  AND   SPEECH.  [chap.  xvi. 

tone,  unsteady,  and  more  restricted  in  extent  :  the  first  defect  is 
owing  to  the  ossification  of  the  cartilages  of  the  larynx  and  the 
altered  condition  of  the  vocal  cord ;  the  want  of  steadiness  arises 
from  the  loss  of  nervous  power  and  command  over  the  muscles ; 
the  result  of  which  is  here,  as  in  other  parts,  a  tremulous 
motion.  These  two  causes  combined  render  the  voices  of  old 
people  void  of  tone,  unsteady,  bleating,  and  weak. 

In  any  class  of  persons  arranged,  as  in  an  orchestra,  according 
to  the  character  of  voices,  each  would  possess,  with  the  general 
characteristics  of  a  bass,  or  tenor,  or  any  other  kind  of  voice, 
some  peculiar  character  by  which  his  voice  would  be  recognised 
from  all  the  rest.  The  conditions  that  determine  these  distinc- 
tions are,  however,  quite  unknown.  They  are  probably  inherent 
in  the  tissues  of  the  larynx,  and  are  as  indiscernible  as  the 
minute  differences  that  characterise  men's  features  ;  one  often 
observes,  in  like  manner,  hereditary  and  family  peculiarities  of 
voice,  as  well  marked  as  those  of  the  limbs  or  face. 

Most  persons,  particularly  men,  have  the  power,  if  at  all 
capable  of  singing,  of  modulating  their  voices  through  a  double 
series  of  notes  of  different  character  :  namely,  the  notes  of  the 
natural  voice,  or  chest-notes,  and  the  falsetto  notes.  The  natural 
voice,  which  alone  has  been  hitherto  considered,  is  fuller,  and 
excites  a  distinct  sensation  of  much  stronger  vibration  and 
resonance  than  the  falsetto  voice,  which  has  more  a  flute-like 
character.  The  deeper  notes  of  the  male  voice  can  be  produced 
only  with  the  natural  voice,  the  highest  with  the  falsetto  only ; 
the  notes  of  middle  pitch  can  be  produced  either  with  the  natural 
or  falsetto  voice ;  the  two  registers  of  the  voice  are  therefore 
not  limited  in  such  a  manner  as  that  one  ends  when  the  other 
begins,  but  they  run  in  part  side  by  side. 

Method  of  the  Production  of  Notes. — The  natural  or 
chest-notes,  are  produced  by  the  ordinary  vibrations  of  the  vocal 
cords.  The  mode  of  production  of  the  falsetto  notes  is  still 
obscure. 

By  Midler  the  falsetto  notes  were  thought  to  be  due  to  vibra- 
tions of  only  the  inner  borders  of  the  vocal  cords.  In  the  opinion 
of  Petrequin  and  Diday,  they  do  not  result  from  vibrations  of  the 
vocal  cords  at  all,  but  from  vibrations  of  the  air  passing  through 
the  aperture   of  the  glottis,  which  they  believe  assumes,  at  such 


chap,  xvi.]  VABIETIES  OF  VOICES.  529 

times,  the  contour  of  the  embouchun  of  a  flute.     Othi  rs  der- 

ing  Bome  degree  of  similarity  which  exists  between  the  falsetto 
notes  and  the  peculiar  turns  called  harmonic,  which  are  produced 
when,    by   touching   or   Btopping   a   harp-string   at  a   particular 

point,  only  a  portion  of  its  length  is  allowed  to  vibrate)  have 
supposed  that,  in  the  falsetto  notes,  portions  of  the  vocal  liga- 
ments are  thus  isolated,  and  made  to  vibrate  while  the  rest  are 
held  still.  The  question  cannot  yet  he  settled;  hut  any  one  in 
the  habit  of  singing  may  assure  himself,  both  by  the  difficulty  of 
passing  smoothly  from  one  set  of  notes  to  the  other,  and  by  the 
necessity  of  exercising  himself  in  both  registers,  lest  he  should 
become  very  deficient  in  one,  that  there  must  be  some  great 
difference  in  the  modes  in  which  their  respective  notes  are 
produced. 

The  strength  of  the  voice  depends  partly  on  the  degree  to  which 
the  vocal  cords  can  be  made  to  vibrate  ;  and  partly  on  the  fitni 
for  resonance  of  the  membranes  and  cartilages  of  the  larynx,  of 
the  parietes  of  the  thorax,  lungs,  and  cavities  of  the  mouth, 
nostrils,  and  communicating  sinuses.  It  is  diminished  by  any- 
thing which  interferes  with  such  capability  of  vibration.  The 
intensity  or  loudness  of  a  given  note  with  maintenance  of  the 
same  "pitch,"  cannot  be  rendered  greater  by  merely  increasing  the 
force  of  the  current  of  air  through  the  glottis;  for  increase  of 
the  force  of  the  current  of  air.  casterti  paribus,  raises  the  pitch 
both  of  the  natural  and  the  falsetto  notes.  Yet,  since  a  singer 
possesses  the  power  of  increasing  the  loudness  of  a  note  from  the 
faintest  "  piano  "  to  "  fortissimo  "  without  its  pitch  being  altered, 
there  must  be  some  means  of  compensating  the  tendency  of  the 
vocal  cords  to  emit  a  higher  note  when  the  force  of  the  current 
of  air  is  increased.  This  means  evidently  consists  in  modifving 
the  tension  of  the  vocal  cords.  When  a  note  is  rendered  louder 
and  more  intense,  the  vocal  cords  must  be  relaxed  by  remission 
of  the  muscular  action,  in  proportion  as  the  force  of  the  current 
of  the  breath  through  the  glottis  is  increased.  "When  a  note  is 
rendered  fainter,  the  reverse  of  this  must  occur. 

The  arches  of  the  palate  and  the  uvula  become  contracted  during 
the  formation  of  the  higher  notes  ;  but  their  contraction  is  the 
>ame  for  a  note  of  given  height,  whether  it  be  falsetto  or  not ; 
and  in  either  case  the  arches  of  the  palate  may  be  touched  with 

M    M 


530  VOICE  AND  SPEECH.  [chap.  xvi. 

the  finger,  without  the  note  being  altered.  Their  action,  there- 
fore, in  the  production  of  the  higher  notes  seems  to  be  merely 
the  result  of  involuntary  associate  nervous  action,  excited  by  the 
voluntarily  increased  exertion  of  the  muscles  of  the  larynx.  If 
the  palatine  arches  contribute  at  all  to  the  production  of  the 
higher  notes  of  the  natural  voice  and  the  falsetto,  it  can  only  be 
by  their  increased  tension  strengthening  the  resonance. 

The  office  of  the  ventricles  of  the  larynx  is  evidently  to  afford  a 
free  space  for  the  vibrations  of  the  lips  of  the  glottis ;  they 
may  be  compared  with  the  cavity  at  the  commencement  of  the 
mouth-piece  of  trumpets,  which  allows  the  free  vibration  of  the 
lips. 

Speech. 

Besides  the  musical  tones  formed  in  the  larynx,  a  great  number 
of  other  sounds  can  be  produced  in  the  vocal  tubes,  between  the 
glottis  and  the  external  apertures  of  the  air-passages,  the  com- 
bination of  which  sounds  by  the  agency  of  the  cerebrum  into 
different  groups  to  designate  objects,  properties,  actions,  etc.. 
constitutes  language.  The  languages  do  not  employ  all  the 
sounds  which  can  be  produced  in  this  manner,  the  combination  of 
some  with  others  being  often  difficult.  Those  sounds  which  are 
easy  of  combination  enter,  for  the  most  part,  into  the  formation 
of  the  greater  number  of  languages.  Each  language  contains  a 
certain  number  of  such  sounds,  but  in  no  one  are  all  brought 
together.  On  the  contrary,  different  languages  are  characterised 
by  the  prevalence  in  them  of  certain  classes  of  these  sounds,  while 
others  are  less  frequent  or  altogether  absent. 

Articulate  Sounds. — The  sounds  produced  in  speech,  or 
articulate  sounds,  are  commonly  divided  into  vowels  and  consonants  : 
the  distinction  between  which  is,  that  the  sounds  for  the  former 
are  generated  by  the  larynx,  while  those  for  the  latter  are  pro- 
duced by  interruption  of  the  current  of  air  in  some  part  of  the 
air-passages  above  the  larynx.  The  term  consonant  has  been 
given  to  these  because  several  of  them  are  not  properly  sounded, 
except  consonantly  icith  a  vowel.  Thus,  if  it  be  attempted  to 
pronounce  aloud  the  consonants  b,  d,  and  g,  or  their  modifications, 
p,  f,  £,  the  intonation  only  follows  them  in  their  combination  with 


chap,  xn.]  BPBECH.  531 

a  rowel.     T<>  recognize  the  essential  properties  of  the  articulate 

sounds,  we  must,  according  to  Midler,  first  examine  them  as  they 
are  produced  in  whispering,  and  then  investigate  which  of  them 
can  also  be  uttered  in  n  modified  character  conjoined  with  ■ 
tone.  By  this  procedure  we  find  two  series  of  sounds:  in 
one  the  sounds  are  mute,  and  cannot  l>e  uttered  with  a  vocal 
tone;  the  sounds  of  the  other  series  can  be  formed  indepen- 
dently <'f  voice,  but  are  also  capable  of  being  uttered  in  conjunc- 
tion with  it. 

All  the  vowels  can  he  expressed  in  a  whisper  without  vocal 
tone,  that  is,  mutely.  These  mute  vowel-sounds  differ,  however, 
in  some  measure,  as  to  their  mode  of  production,  from  the 
consonants.  All  the  mute  consonants  are  formed  in  the  vocal 
tube  above  the  glottis,  or  in  the  cavity  of  the  mouth  or  nose,  by 
the  mere  rushing  of  the  air  between  the  surfaces  differently 
modified  in  disposition.  But  the  sound  of  the  vowels,  even  when 
mute,  has  its  source  in  the  glottis,  though  its  vocal  cords  are  not 
thrown  into  the  vibrations  necessary  for  the  production  of  voice  ; 
and  the  sound  seems  to  be  produced  by  the  passage  of  the  current 
of  air  between  the  relaxed  vocal  cords.  The  same  vowel  sound 
can  be  produced  in  the  larynx  when  the  mouth  is  closed,  the 
nostrils  being  open,  and  the  utterance  of  all  vocal  tone  avoided. 
This  sound,  when  the  mouth  is  open,  is  so  modified  by  varied 
forms  of  the  oral  cavity,  as  to  assume  the  characters  of  the  vowels 
a,  c,  i,  0,  v.,  in  all  their  modifications. 

The  cavitv  of  the  mouth  assumes  the  same  form  for  the 
articulation  of  each  of  the  mute  vowels  as  for  the  corresponding 
vowel  when  vocalized  ;  the  only  difference  in  the  two  cases  lies 
in  the  kind  of  sound  emitted  by  the  larynx.  Krantzenstein  and 
Kempelen  have  pointed  out  that  the  conditions  necessary  for 
changing  one  and  the  same  sound  into  the  different  vowels,  are 
differences  in  the  size  of  two  parts — the  oral  canal  and  the  oral 
Opening  ;  and  the  same  is  the  case  with  regard  to  the  mute 
vowels.  By  oral  canal,  Kempelen  means  here  the  space  between 
the  tongue  and  palate  :  for  the  pronunciation  of  certain  vowels 
both  the  opening  of  the  mouth  and  the  space  just  mentioned  are 
widened  ;  for  the  pronunciation  of  other  vowels  both  are  con- 
tracted;  and  for  others  one  is  wide,  the  other  contracted. 
Admitting  five  degrees  of  size,  both  of  the  opening  of  the  mouth 

M  m  2 


532  VOICE  AND   SPEECH.  [chap.  xvi. 

and  of  the  space  between  the  tongue  and  palate,  Keinpelen  thus 
states  the  dimensions  of  these  parts  for  the  following  vowel 
sounds  : — 

Vowel.  Pound.       Size  of  oral  opening.  Size  of  oral  canal. 

a    as  in "  far "  5  ...  3 

a         ,,     "name"  4  ...  2 

e         ..     "  theme "  3  1 

0        „    "go"  2  ...  4 

00      .,    "  cool :'  1  ...  5 

Another  important  distinction  in  articulate  sounds  is,  that  the 
utterance  of  some  is  only  of  momentary  duration,  taking  place 
during  a  sudden  change  in  the  conformation  of  the  mouth,  and 
being  incapable  of  prolongation  by  a  continued  expiration.  To 
this  class  belong  l>,  p,  d,  and  the  hard  g.  In  the  utterance  of 
other  consonants  the  sounds  may  be  continuous ;  they  may  be 
prolonged,  ad  libitum,  as  long  as  a  particular  disposition  of  the 
mouth  and  a  constant  expiration  are  maintained.  Among  these 
consonants  are  h,  on,  n,  f,  s,  r,  I.  Corresponding  differences  in 
respect  to  the  time  that  may  be  occupied  in  their  utterance  exist 
in  the  vowel  sounds,  and  principally  constitute  the  differences  of 
long  and  short  syllables.  Thus  the  a  as  in  "for"  and  "fate," 
the  0  as  in  "go"  and  "fort,''  may  be  indefinitely  prolonged; 
but  the  same  vowels  (or  more  properly  different  vowels  expressed 
by  the  same  letters),  as  in  "can"  and  "fact,"  in  "dog"  and 
"  rotten,"  cannot  be  prolonged. 

All  sounds  of  the  first  or  explosive  kind  are  insusceptible  of 
combination  with  vocal  tone  ("  intonation  "),  and  are  absolutely 
mute  ;  nearly  all  the  consonants  of  the  second  or  continuous 
kind  may  be  attended  with  "intonation." 

Ventriloquism. — The  peculiarity  of  speaking,  to  which  the 
term  ventriloquism  is  applied,  appears  to  consist  merely  in  the 
varied  modification  of  the  sounds  produced  in  the  larynx,  in 
imitation  of  the  modifications  which  voice  ordinarily  suffers  from 
distance,  etc.  From  the  observations  of  Midler  and  Colombat,  it 
seems  that  the  essential  mechanical  parts  of  the  process  of  ven- 
triloquism consist  in  taking  a  full  inspiration,  then  keeping  the 
muscles  of  the  chest  and  neck  fixed,  and  speaking  with  the  mouth 
almost  closed,  and  the  lips  and  lower  jaw  as  motionless  as  possible, 
while  air  is  very  slowly  expired  through  a  very  narrow  glottis ; 


CHAP,  xvir.]     IXCOME  AND   EXPENDITURE  OF   BODY.  533 

care  being  taken  also,  that  none  of  the  expired  air  passes  through 
the  nose.  But,  as  observed  by  Midler,  much  of  the  ventriloquist's 
skill  in  imitating  the  voices  coming  from  particular  directions, 
consists  in  deceiving  other  senses  than  hearing.  We  never  dis- 
tinguish very  readily  the  direction  in  which  sounds  reach  our 
ear;  and,  when  our  attention  is  directed  to  a  particular  point, 
our  imagination  is  very  apt  to  refer  to  that  point  whatever  sounds 
we  may  hear. 

Action  of  the  Tongue  in  Speech.  —  The  tongue,  which  is 
usually  credited  with  the  power  of  speech — language  and  speech 
being  often  employed  as  synonymous  terms — plays  only  a  sub- 
ordinate, although  very  important  part.  This  is  well  shown  by 
cases  in  which  nearly  the  whole  organ  has  been  removed  on 
account  of  disease.  Patients  who  recover  from  this  operation 
talk  imperfectly,  and  their  voice  is  considerably  modified ;  but  the 
loss  of  speech  is  confined  to  those  letters  in  the  pronunciation  of 
which  the  tongue  is  concerned. 

Stammering  depends  on  a  want  of  harmony  between  the 
action  of  the  muscles  (chiefly  abdominal)  which  expel  air  through 
the  larynx,  and  that  of  the  muscles  which  guard  the  orifice  (rima 
glottidis)  by  which  it  escapes,  and  of  those  (of  tongue,  palate,  etc.) 
which  modulate  the  sound  to  the  form  of  speech. 

Over  either  of  the  groups  of  muscles,  by  itself,  a  stammerer 
may  have  as  much  power  as  other  people.  But  he  cannot 
harmoniously  arrange  their  conjoint  actions. 


CHAPTEE  XVIL 

NTJTBITION  ;   THE    INCOME   AND   EXPENDITURE   OF  THE 

HUMAN   BODY. 

The  various  physiological  processes  which  occur  in  the  human 
body  have,  with  the  exception  of  those  in  the  nervous  and  gene- 
rative systems,  which  will  be  considered  in  succeeding  chapters, 
now  been  dealt  with,  and  it  will  be  as  well  to  give  in  this  chapter 
on  Nutrition  a  summary  of  what  has  been  considered  more  at 
length  before. 


534  INCOME  AXD  EXPENDITURE   OF  BODY.     [chap.  xyii. 

The  subject  may  be  considered  under  the  following  heads. 
(i).  The  Evidence  and  Amount  of  Expenditure.  (2).  The 
Sources  and  Amount  of  Income.  (3).  The  Sources  and  Objects 
of  Expenditure. 

1.  Evidence  and  Amount  of  Expenditure. — The  evidence 
of  Expenditure  by  the  living  body  is  abundantly  complete. 

From  the  table  (p.  262)  it  will  be  seen  how*  the  various  amounts 
of  the  excreta  are  calculated. 

From  the  Lungs  there  is  exhaled  every  24  hours, 

Of  Carbonic  Acid,  about     ....     15.000  grains 

..  "Water 5;ooo       „ 

Traces  of  organic  matter. 

From  the  Skin — 

Water 11,500  grains 

Solid  and  gaseous  matter         .        .        .     .         250 

From  the  Kidneys — 

Water 23,000  grains 

Organic  matter 680       ., 

Minerals  or  salines       .....  420       ., 

From  tJte  Intestines — 

Water .       2.000  grains 

Various  organic  and  mineral  substances      .  800       ,, 

In  the  account  of  Expenditure,  must  be  remembered  in  addi- 
tion the  milk  (during  the  period  of  suckling),  and  the  products 
of  secretion  from  the  generative  organs  (ova,  menstrual  blood, 
semen)  ;  but,  from  their  variable  and  uncertain  amounts,  these 
cannot  be  reckoned  with  the  preceding. 

Altogether,  the   Expenditure  of  the  body  represented  by  the 
sum  of  these  various  excretory  products  amounts  every  24  hours 
to- 
Solid  and  gaseous  matter    ....     17.150  grains  (1,1 13  grms.) 
Water  (either  fluid  or  combined  with  the 

solids  and  gaseous  matter)  .         .         .     .     49.500      ,,       (2.695       jj     ) 

The  matter  thus  lost  by  the  body  is  matter  the  chemical 
attractions  of  which  have  been  in  great  part  satisfied  ;  and  which 
remains  quite  useless  as  food,  until  its  elements  have  been  again 
separated  and  re-arranged  by  members  of  the  vegetable  world 
(pp.  2  and  3).  It  is  especially  instructive  to  compare  the  chemical 
constitution  of  the  products  of  expenditure,  thus  separated  by  the 


CHAP.  XVII.]       SOURCES   AND    AMOUNT    Of    I.Vn.MK.  535 

various  excretory  organs,  with  that  of  the  sources  of  income  to  be 
immediately  considered. 

It  is  evident  from  these  facts  that  if  the  human  body  is  to 
maintain  its  size  and  composition,  there  must  be  added  to  it 
matter  corresponding  in  amount  with  that  which  is  Lost.  The 
income  must  equal  the  expenditure. 

2.  Sources  and  Amount  of  Income. — The  Income  of  the 
body  consists  partly  of  Food  and  Drink,  and  partly  of  Oxygen. 

Into  the  stomach  there  is  received  daily  : — 

Solid  (chemically  dry)  food         .         .  8,000  grains  (520  grms.) 

Water  (as  water,  or  variously  combined 
with  solid  food) 35,000-40,000      .,     (2.444     »     ) 

By  the  Lungs  there  is  absorbed  daily  : — 

Oxygen 13,000      „       (844     .,     ) 

The  average  total  daily  receipts,  in  the  shape  of  food,  drink  and 
oxygen,  correspond,  therefore,  with  the  average  total  daily  expen- 
diture, as  shown  by  the  following  table. 


Income. 

Solid  food    .         .         .     8.000  grains 
Water     .         .         .     .  37,650     ,, 
Oxygen       .         .        .  13.000     ., 


(about  3.808  grms.,  or  8^1b.) 


Expenditure. 

Lungs  .        .         .  20.ooograins. 

Skin        .         .         .     .  11.750     „ 
Kidneys       .         .         .24.100      ., 
Intestines        .         .     .     2,800      ,, 
58,650  grains   j    (Generative  and  mam- 
mary-gland products 
are  supposed   to  be 
included.) 


58,650  grains 
(About  3808  grms.) 

These  quantities  are  approximate  only.  But  they  may  be  taken 
as  fair  averages  for  a  healthy  adult.  The  absolute  identit}T  of  the 
two  numbers  (in  grains)  in  the  two  tables  is  of  course  diagram- 
matic. No  such  exactitude  in  the  account  occurs  in  any  living 
body,  in  the  course  of  any  given  twenty-four  hours.  But  any 
difference  which  exists  between  the  two  amounts  of  income  and 
expenditure  at  any  given  period,  corresponds  merely  with  the 
slight  variations,  in  the  amount  of  capital,  (weight  of  body)  to 
which  the  healthiest  subject  is  liable. 

The  chemical  composition  of  the  food   (p.  264)  may  be  profit- 


536  INCOME  AXD  EXPENDITURE   OF   BODY.    [chap.  xvii. 

ably  compared  with  that  of  the  excreta,  as  before  mentioned. 
The  greater  part  of  our  food  is  comprised  of  mutter,  which  contains 
much  potential  energy  ;  and  in  the  chemical  changes  (combustion 
and  other  processes),  to  which  it  is  subject  in  the  body,  active 
energy  is  manifested. 

3.  The  Sources  and  Objects  of  Expenditure. — The  sources 
of  necessary  waste  and  expenditure  in  the  living  body  are  various 
and  extensive.  They  may  be  comprehended  under  the  following 
heads: — (1)  Common  wear  and  tear;  such  as  that  to  which  all 
structures,  living  and  not  living,  are  subjected  by  exposure  and 
work  :  but  which  must  be  especially  large  in  the  soft  and  easily 
decaying  structures  of  an  animal  body. 

(2)  Manifestations  of  Force  in  the  form  either  of  Heat  or  Motion. 
In  the  former  case  (Heat),  the  combustion  must  be  sufficient  to 
maintain  a  temperature  of  about  ioo°  F.  (3  7  "8°  C.)  throughout 
the  whole  substance  of  the  body,  in  all  varieties  of  external  tem- 
perature, notwithstanding  the  large  amount  continually  lost  in 
the  ways  previously  enumerated  (p.  387).  In  the  case  of  Motion, 
there  is  the  expenditure  involved  in  (a)  Ordinary  muscular  move- 
ments, as  in  Prehension,  Mastication,  Locomotion,  and  numberless 
other  ways  :  (b)  Various  involuntary  movements,  as  in  Respira- 
tion, Circulation,  Digestion,  &c. 

(3)  Manifestation  of  Nerve-force;  as  in  the  general  regulation  of 
all  physiological  processes,  e.g.,  Respiration,  Circulation,  Diges- 
tion; and  in  Volition  and  all  other  manifestations  of  cerebral 
activity. 

(4)  The  energy  expended  in  aU  physiological  processes,  e.g.,  Nutri- 
tion, Secretion,  Growth,  and  the  like. 

The  Total  expenditure  or  manifestation  of  energy  by  an  animal 
body  can  be  measured,  with  fair  accuracy ;  the  terms  used  being 
such  as  are  employed  in  connection  with  other  than  vital  opera- 
tions. All  statements,  however,  must  be  considered  for  the  present 
approximate  only,  and  especially  is  this  the  case  with  respect 
to  the  comparative  share  of  expenditure  to  1  >e  assigned  to  the 
various  objects  just  enumerated. 

The  amount  of  energy  daily  manifested  by  the  adult  human 
body  in  (a)  the  maintenance  of  its  temperature  ;  (b)  in  internal 
mechanical  work,  as  in  the  movements  of  the  respiratory  muscles, 
the    heart,    Arc.  :     and   (c)    in    external    mechanical    work,    as    in 


chap,  xvn.]  SOURCES   OF   EUROS.  537 

locomotion  and  all  other  voluntary  movements,  has  hern  reckoned 
at  about  ;v4°()  foot-tons  (p.  154).  Of  this  amount  only  one-tenth 
is  directly  expended  in  internal  and  external  mechanical  work  ; 
the  remainder  being  employed  in  the  maintenance  of  the  body's 
heat.  The  latter  amount  represents  the  heat  which  would  he 
required  t<>  raise  4S-4  lb.  of  water  from  the  freezing  to  the  boiling 
point;  or  if  converted  into  mechanical  power,  it  would  suffice 
to  raise  the  body  of  a  man  weighing  about  150  11).  through  a 
vertical  height  of  8 J,  miles. 

To  the  foregoing  amounts  of  expenditure  must  be  added  the 
(piite  unknown  quantity  expended  in  the  various  manifestations 
of  nerve-force,  and  in  the  work  of  nutrition  and  growth  (using 
these  terms  in  their  widest  sense).  By  comparing  the  amount 
of  energy  which  should  be  produced  in  the  body  from  so  much 
food  of  a  given  kind,  with  that  which  is  actually  manifested  (as 
shown  by  the  various  products  of  combustion,  in  the  excretions) 
attempts  have  been  made,  indeed,  to  estimate,  by  a  process  of 
exclusion,  these  unknown  quantities;  but  all  such  calcula- 
tions must  be  at  present  considered  only  very  doubtfully 
approximate. 

Sources  of  Error. — Among  the  sources  of  error  in  any  such 
calculations  must  be  reckoned,  as  a  chief  one,  the,  at  present, 
entirely  unknown  extent  to  which  forces  external  to  the  body 
(mainly  heat)  can  be  utilised  by  the  tissues.  We  are  too  apt  to 
think  that  the  heat  and  light  of  the  sun  are  directly  correlated, 
as  far  as  living  beings  are  concerned,  with  the  chemico-vital 
transformations  involved  in  the  nutrition  and  growth  of  the 
members  of  the  vegetable  world  only.  But  animals,  although 
comparatively  independent  of  external  heat  and  other  forces, 
probably  utilise  them,  to  the  degree  occasion  offers.  And  although 
the  correlative  manifestation  of  energy  in  the  body,  due  to 
external  heat  and  light,  may  still  be  measured  in  so  far  as  it  may 
take  the  form  of  mechanical  work ;  yet,  in  so  far  as  it  takes  the 
form  of  expenditure  in  nutrition  or  nerve-force,  it  is  evidently 
impossible  to  include  it  by  any  method  of  estimation  yet  dis- 
covered; and  all  accounts  of  it  must  be  matters  of  the  purest 
theory.  These  considerations  may  help  to  explain  the  apparent 
discrepancy  between  the  amount  of  energy  which  is  capable  of 
being  produced  by  the  usual  daily  amount  of  food,   with  that 


538  INCOME  AXD   EXPENDITURE   OF  BODY.        [chap.  xvir. 

which  is  actually  manifested  daily  by  the  body ;  the  former 
leaving  but  a  small  margin  for  anything  beyond  the  maintenance 
of  heat,  and  mechanical  work. 

In  the  foregoing  sketch  we   have  supposed  that   the  excreta 
are  exactly  replaced  by  the  ingesta. 


Nitrogenous  Equilibrium  and  Formation  of  Fat. 

If  an  animal,  which  has  undergone  a  starving  period,  be  fed 
upon  a  diet  of  lean  meat,  it  is  found  that  instead  of  the  greater 
part  of  the  nitrogen  being  stored  up,  as  one  would  expect,  the  chief 
part  of  it  appears  in  the  urine  as  urea,  and  on  continuing  with 
the  diet  the  excreted  nitrogen  approximates  more  and  more 
closely  to  the  ingested  nitrogen  until  at  last  the  amounts  are  equal 
in  both  cases.  This  is  called  nitrogenous  equilibrium.  There 
may,  however,  be  at  the  same  time  an  increase  of  weight 
which  is  due  to  the  putting  on  of  fat.  If  this  is  the  case  it  must 
be  apparent  that  the  protoplasm  of  the  tissues  is  able  to  form  fat 
out  of  proteid  material  and  to  split  it  up  into  urea  and  fat.  If 
fat  be  given  in  small  quantities  with  the  meat,  for  a  time  the 
carbon  of  the  egesta  and  ingesta  are  equal,  but  if  the  fat  be 
increased  beyond  a  certain  point  the  body  weight  increases  from 
a  deposition  of  fat  ;  not,  however,  by  a  mere  mechanical  deposi- 
tion or  filtration  from  the  blood,  but  by  an  actual  act  of  secretion 
by  the  protoplasm  whereby  the  fat  globules  are  stored  up  within 
itself.  In  a  similar  manner  as  regards  carbo-hydrates,  if  they  are  in 
small  quantity,  the  whole  of  the  carbon  appears  in  the  excreta,  but 
beyond  a  certain  amount  a  considerable  portion  of  it  is  retained  in 
fat,  having  been  by  the  protoplasm  stored  up  within  itself  in  that 
material.  The  amount  of  proteid  material  required  to  produce 
nitrogenous  equilibrium  is  considerable,  but  it  may  be  materially 
diminished  by  the  addition  of  carbo-hydrate  or  fatty  food  or  of 
gelatine  to  the  exclusively  meat  diet. 

It  is  of  much  interest  to  consider  how  the  protoplasm  acts 
in  converting  food  into  energy  and  decomposition  products, 
since  the  substance  itself  does  not  undergo  much  change 
in  the  process  except  a  slight  amount  of  wear  and  tear. 
We  may  assume  that  it  is  the  property  of  protoplasm  to   sepa- 


chap.  xvn. J  USES  OF   POOD.  539 

rate    from   the    blood   the    materials    which    may    be    required   to 

produce  secretions,  in  the   ease  of  the  protoplasm   of  Becreting 

-lands,  or  to  evolve  heat  and  energy,  aa  in  tin  case  of  the  pro- 
toplasm  of  muscle.  The  Bubstancea  are  very  possibly  different 
for  each  process,  and  the  decomposition  products,  too,  may 
be  different  in  quality  or  quantity.  Proteid  materials  appear 
to  be  specially  needed,  as  is  shown  by  the  invariable  presenc 
area  in  the  urine  even  during  starvation ;  and  as  in  the  latter 

.  there  has  been  no  food  from  which  these  materials  could 
have  been  derived,  the  urea  is  considered  to  be  derived  from  the 
disintegration  of  the  nitrogenous  tissues  themselves.  The 
removal  of  all  fat  from  the  body  in  a  starvation  period,  as  the 
apparent  change,  would  lead  to  the  supposition  that  fat  is 
also  a  specially  necessary  pabulum  for  the  production  of  proto- 
plasmic energy;  and  the  fact  that,  as  mentioned  above,  with  a 
diet  of  lean  meat  an  enormous  amount   appears  to  be   required, 

vests  that  in  that  case  protoplasm  obtains  the  fat  it  needs 
from  the  proteid  food,  which  process  must  be  evidently  a  source 
of  much  waste  of  nitrogen.  The  idea  that  proteid  food  has  two 
destinations  in  the  economy,  viz.,  to  form  organ  or  tissue  proteid 
which  builds  up  organs  and  tissues,  and  circulating  proteid,  from 
which  the  organs  and  tissues  derive  the  materials  of  their  secre- 
tions or  for  producing  their  energy,  is  a  convenient  one,  as 
it  is  unlikely  that  protoplasm  would  go  to  the  expense  of  con- 
struction simply  for  the  sake  of  immediate  destruction. 


540  TIIE  NERVOUS   SYSTEM.  [chap,  xvirr. 


CHAPTER    XVIII. 

THE    NERVOUS    SYSTEM. 

Chief  Divisions  of  the  Nervous  System. — The  Nervous 
System  consists  of  two  portions  or  systems,  the  (1)  Cerebrospinal, 
and  the  (2)  Sympathetic. 

(I.)  The  Cerebrospinal  system  includes  the  Brain  and  Spinal 
cord,  with  the  nerves  proceeding  from  them.  Its  fibres  are 
chiefly,  but  not  exclusively,  distributed  to  the  skin  and  other 
organs  of  the  senses,  and  to  the  voluntary  muscles. 

(II.)  The  Sympathetic  Xervous  system  consists  of: — (i)  A 
double  chain  of  ganglia  and  fibres,  which  extends  from  the  cranium 
to  the  pelvis,  along  each  side  of  the  vertebral  column,  and  from 
which  branches  are  distributed  both  to  the  cerebro-spinal  system, 
and  to  other  parts  of  the  sympathetic  system.  With  these  may 
be  included  the  small  ganglia  in  connection  with  those  branches 
of  the  fifth  cerebral  nerve  which  are  distributed  in  the  neighbour- 
hood of  the  organs  of  special  sense  :  namely,  the  ophthalmic,  otic, 
sphenopalatine,  and  submaxillary-ganglm.  (2)  Various  ganglia 
and  plexuses  of  nerve-fibres  which  give  off  branches  to  the  thoracic 
and  abdominal  viscera,  the  chief  of  such  plexuses  being  the 
Cardiac,  Solar,  and  Hypogastric  ;  but  in  intimate  connection  with* 
these  are  many  secondary  plexuses,  as  the  aortic,  spermatic,  and 
renal.  To  these  plexuses,  fibres  pass  from  the  prevertebral  chain 
of  ganglia,  as  well  as  from  cerebro-spinal  nerves.  (3)  Various 
ganglia  and  plexuses  in  the  substance  of  many  of  the  viscera,  as 
in  the  stomach,  intestines,  and  urinary  bladder.  These,  which  are, 
for  the  most  part,  microscopic,  also  freely  communicate  with  other 
parts  of  the  sympathetic  system,  as  well  as,  to  some  extent,  with 
the  cerebro-spinal.  (4)  By  many,  the  ganglia  on  the  posterior- 
roots  of  the  spinal  nerves,  on  the  glossopharyngeal  and  vagus,  and 
on  the  sensory  root  of  the  fifth  cerebral  nerve  (Gasserian  ganglion), 
are  also  included  as  sympathetic-nerve  structures. 

Elementary  Structure. — The  organs  both  of  the  Cerebro- 
spinal and   Sympathetic  nervous   systems  are   composed    of  two 


chap.xviii.]         STRUCTURE   OF   NTEKVE   FIBRES. 


541 


structural  elements — -fibres  and  cells.  The  cells  are  collected  in 
ind  are  always  mingled,  more  or  less,  with  fibres;  such  a 
collection  of  cellular  and  fibrous  nerve-structure  being  termed  a 
nerve-centre.  The  fibres,  besides  entering  into  the  composition  of 
nerve-centres,  form  by  themselves  the  nerves,  which  connect  the 
various  centres,  and  are  distributed  in  the  several  parts  of  the 
body. 

Nerve  Fibres. 

Structure. — Each  nerve-trunk  is  composed  of  a  variable  number 
of  different-sized  bundles  (funiculi)  of  nerve-fibres  which  have  a 
special  sheath    (perineurium  or  neurilemma).     The    funiculi  are 


A 1:  V  1 


Fig.  302. — Transverse  section  of  the  sciatic  nerve  of  a  cot  x  100.— It  consists  of  bundles 
(Funiculi)  of  nerve-fibres  ensheathed  in  a  fibrous  supporting  capsule,  epineunum,  A  ; 
eacb  bundle  has  a  special  sheath  fnot  sufficiently  worked  out  from  the  epineunum  in 
the  figure)  or  perineurium  B;  the  nerve-fibres  N/are  separated  from  one  another  by 
emdoneurium  ;  L,  lymph  spaces  ;  Ar,  artery  ;  Y,  vein  ;  F,  fat.     (V.  D.  Harris., 

enclosed  in  a  firm  fibrous  sheath  (epineurium) ;  this  sheath  also 
sends  in  processes  of  connective  tissue  which  connect  the  bundles 
together.  In  the  funiculi  between  the  fibres  is  a  delicate  sup- 
porting tissue  (the  endoneurium). 

There  are  numerous  lymph-spaces  both  beneath  the  connective- 
tissue  investing  individual  nerve-fibres,  and  also  beneath  that 
which  surrounds  the  funiculi. 

Varieties. — In  most  nerves,  two  kinds  of  fibres  are  mingled  ; 
those  of  one  kind  being  most  numerous  in,  and  characteristic  of, 


542 


THE  NERVOUS   SYSTEM. 


[CHAP.   XVIII. 


nerves  of  the  Cerebrospinal  system  ;  those  of  the  other,  most 
numerous  in  nerves  of  the  Sympathetic  system.  These  are  called 
(a)  medullated  or  white  fibres,  and  (b)  non-medullated  or  grey  fibres. 
(a).  Medullated  Fibres. — Each  medullated  nerve-fibre  is  made 
up  of  the  following  parts  : — (i.)  Primitive  nerve  sheath,  or  nu- 
cleated sheath  of  Schwann.  (2)  Me- 
dullary sheath,  or  white  substance  of 
Schwann.  (3)  Axis-cylinder,  primitive 
band,  axis  band,  or  axial  fibre. 

Although  these  parts  can  be  made 
out   in   nerves    examined    some    time 
after  death,  in  a  recent  specimen  the 
contents  of  the   sheath  appear  to  be 
homogeneous.     But   by  degrees  they 
undergo  changes  which  show  them  to 
be  composed  of  two  different  materials. 
The  internal  or  central  part,  occupying 
the   axis   of  the    tube    (axis-cylinder), 
becomes  greyish,  while  the  outer,  or 
cortical    portion    (white    substance    of 
Schwann),  becomes  opaque  and  dimly 
granular  or  grumous,  as  if  from  a  kind 
of  coagulation.      At  the  same   time, 
the    fine    outline    of    the    previously 
transparent    cylindrical    tube    is    ex- 
changed  for  a    dark    double   contour 
(fig. 303,  b),  the  outer  line  being  formed 
by  the  sheath  of  the   fibre,  the  inner 
by  the  margin  of  curdled   or  coagu- 
lated medullary  substance.    The  granular  material  shortly  collects 
into  little  masses,  which  distend  portions  of  the  tubular  mem- 
brane ;  while  the  intermediate  spaces  collapse,  giving  the  fibres  a 
varicose,  or  beaded  appearance  (fig.  3C3,  c  and  d),  instead  of  the 
previous  cylindrical   form.      The   whole   contents   of  the   nerve- 
tubules  are  extremely  soft,  for  when  subjected  to  pressure  they 
readily  pass  from  one  part  of  the  tubular  sheath  to  another,  and 
often  cause  a  bulging  at  the  side  of  the  membrane.     They  also 
readily  escape,  on  pressure,  from  the  extremities  of  the  tubule,  in 
the  form  of  a  grumous  or  granular  material. 


Fig.  303.  —  Primitive   nerve-fibres. 

a.  A  perfectly  fresh  tubule  with 
a  single  dark  outline.  b.  A 
tubule  or  hbre  with  a  double 
contour  from  commencing  post- 
mortem change,  c.  The  changes 
further  advanced,  producing  a 
varicose  or  beaded  appearance 
n.  A  tubule  or  fibre,  the  central 
part  of  which,  in  consequence  of 
still  further  changes,  has  accu- 
mulated in  separate  portions 
within  the  sheath  (Wagner). 


CHAP,  win.] 


STRUCTURE  OF   NERVE   FIBRES. 


543 


The    nucleated    sheath   of  Schwann   is  a    pellucid   membrane, 
forming  the  outer  investment   of  the   nerve-fibre.     Within  this 

delicate    structureless    membrane    nuclei    are    seen    at    intervals, 

surrounded  by  a  variable  amount  of  protoplasm.  The  sheath  is 
structureless,  like  the  sarcolemma,  and  the  nuclei  appear  to  l>e 
within  it  :  together  with  the  protoplasm 
■which  surrounds  them,  they  are  the  relics 
of  embryonic  cells,  and  from  their  resem- 
blance to  the  muscle  corpuscles  of  striated, 
muscle,  may  be  termed  nerve-corpuscles. 

(2.)  The  medullary  slveath  or  white  sub- 
stance of  Schwann  is  the  part  to  which  the 
peculiar  white  aspect  of  the  cerebro-spinal 
nerves  is  principally  due.  It  is  a  thick, 
fatty,  semi-fluid  substance,  as  we  have  seen, 
possessing  a  double  contour.  It  is  said  to 
be  made  up  of  a  fine  reticulum  (Stilling, 
Klein),  in  the  meshes  of  which  is  embedded 
the  bright  fatty  material. 

According  to  McCarthy,  the  medullary 
sheath  is  composed  of  small  rods  radiating 
from  the  axis-cylinder  to  the  sheath  of 
Schwann.  Sometimes  the  whole  space  is 
occupied    by   these    rods,    whilst   at  other 

times  the  rods  appear  shortened,  and  compressed  laterally  into 
bundles  embedded  in  some  homogeneous  substance. 

(3.)  The  axis-cylinder  consists  of  a  large  number  of  primitive 
fibrillce.  This  is  well  shown  in  the  cornea,  where  the  axis- 
cylinders  of  nerves  break  up  into  minute  fibrils  which  go  to  form 
terminal  networks  (see  Cornea),  and  also  in  the  spinal  cord,  where 
these  fibrillar  form  a  large  part  of  the  grey  matter.  From  various- 
considerations,  such  as  its  invariable  presence  and  unbroken  con- 
tinuity in  all  nerves,  though  the  primitive  sheath  or  the  medullary 
sheath  may  be  absent,  there  can  be  little  doubt  that  the  axis- 
cylinder  is  the  conductor  of  nerve-force,  the  other  parts  of  the 
nerve  having  the  subsidiary  function  of  support  and  possibly  of 
insulation. 

At  regular  intervals  in  most  medullated  nerves,  the  nucleated 
sheath    of    Schwann    possesses    annular   constrictions   (nodes    of 


Fig.  304. — Two  nerve-fibres 
of  sciatic  nerve,  a.  Node 
of  Eanvier.  b.  Axi — 
cylinders,  c.  Sheath  of 
Schwann,  with  nuclei . 
X  300.  (Klein  and  Xoble 
Smith.) 


544 


THE  NEBVOUS  SYSTEM. 


[chat.  XVIII. 


Eanvier).  At  these  points  (figs.  304,  305),  the  continuity  of  the 
medullary  white  substance  is  interrupted,  and  the  primitive 
sheath  comes  into  immediate  contact  with  the  axis-cylinder. 

Size.  —  The  size  of  the  nerve -fibres 
varies,  and  the  same  fibres  do  not  pre- 
serve the  same  diameter  through  their 
whole  length,  being  largest  in  their  course 
within  the  trunks  and  branches  of  the 
nerves,  in  which  the  majority  measure 
from  aox00  to  -30V0  °f  an  mca  m  diameter. 
As  they  approach  the  brain  or  spinal  cord, 
and  generally  also  in  the  tissues  in  which 
they  are  distributed,  they  gradually  become 
smaller.  In  the  grey  or  vesicular  substance 
of  the  brain  or  spinal  cord,  they  generally 
do   not   measure  more  than  from  y^-y   to 

(b.)  Won  -  medullated  Fibres.  —  The 
fibres  of  the  second  kind  (fig.  306),  which 
constitute  the  whole  of  the  branches  of  the 
olfactory  and  auditory  nerves,  the  principal 
part  of  the  trunk  and  branches  of  the  sym- 
pathetic nerves,  and  are  mingled  in  various 
proportions  in  the  cerebro-spinal  nerves, 
differ  from  the  preceding,  chiefly  in  their  fine- 
ness, being  only  about  i  or  ±  as  large 
in  their  course  within  the  trunks  and 
branches  of  the  nerves ;  in  the  absence 
of  the  double  contour  ;  in  their  contents  being  apparently 
uniform  ;  and  in  their  having,  when  in  bundles,  a  yellowish  grey 
hue  instead  of  the  whiteness  of  the  cerebro-spinal  nerves.  These 
peculiarities  depend  011  their  not  possessing  the  outer  layer  of 
medullary  nerve-substance  ;  their  contents  being  composed  exclu- 
sively of  the  axis-cylinder.  Yet,  since  many  nerve-fibres  may  be 
found  which  appear  intermediate  in  character  between  these  two 
kinds,  and  since  the  large  fibres,  as  they  approach  both  their 
central  and  their  peripheral  end,  gradually  diminish  in  size,  and 
assume  many  of  the  other  characters  of  the  fine  fibres  of  the  sym- 
pathetic system,  it  is  not  necessary  to  suppose  that  there  is  any 
material  difference  in  the  two  kinds  of  fibres. 


Fig.  305. — A  node  of  Ean- 
vier in  a  meduUated 
nerve-fibre,  viewed  from 
above.  The  medullary 
sheath  is  interrupted, 
and  the  primitive 
sheath  thickened.  Co- 
pied from  Axel  Key 
and  Eetzius.  X  750. 
(Klein  and  Xoble 
Smith.) 


CRAP.  XVIII.] 


COURSE   OF   NERVE    FIBRES. 


545 


It  is  worthy  of  Dote,  that  in  the  foetus,  at  an  early  period  of 
elopment,  all  nerve-fibres  are  non-medullated. 


A 


1  ig.  306— Grey,  pale,  or  gelatinous  nerve-fibrea.  A.  From  a  braneh  of  the  olfactorv  nerve 
of  the  sheep;  a,  a,  two  dark-bordered  or  white  fib  res  from  the  fifth  pair,  associated 
with  the  pale  olfactory  fibres.  B.  From  the  sympathetic  nerve,  x  4=;o  Mas 
Schult/.'  .  '  ^ 


Course. — Every    nerve-tibre   in   its    course  proceeds  'uninter- 
ruptedly from  its  origin  in  a  nerve-centre  to  near   its  destination, 
whether  this   be  the   periphery  of 
the   body,   another  nervous  centre, 
or    the     same     centre    alienee     it 
issued. 

Bundles  of  fibres  run  together  in 
the  nerve-trunk,  but  merely  lie  in 
apposition  with  each  other  ;  they 
<do  not  unite  :  even  when  they 
anastomose,  there  is  no  union  of 
fibres,  but  onlv  an  interchange  of 
fibres    between    the    anastomosing 

© 

funiculi.  Although  each  nerve-til >re 
is  thus  single  and  undivided  through 
nearly  its  whole  course,  yet  as  it 
approaches  the  region  in  which  it 
terminates,  individual  fibres  break 
up  into  several  subdivisions  (fig. 
308)  before  their  final  ending. 
The  medullated  nerve-fibres,  more- 
over,   lose    their    medullary    sheath    before  their    final   distribu- 

x  S 


Fig.  307. — Several  fibres  of  a  bundle  of 
medullated  m  rve-fibres  acted  upon  by 
silver  nitrate  to  show  peculiar  beha- 
viour of  nodes  of  Ranvier  towards 
their  reagent.  The  silver  has  pene- 
trated at  the  nodes,  and  has  stained 
the  axis-cylinder  for  a  short  distance. 
(Klein  and  Noble  Smith.) 


546 


THE  NERVOUS    SYSTEM. 


[chap.  XVIII. 


tiou,  and  acquire  the  characters  more  or  less  of  non-niedullated 
fibres. 


Fig1.  308. — SmiH   branch  of  a  muscular  nerve  of  ths  jro<j,  near  its  termination,   showing- 
divisions  of  the  fibres,     a,  into  two  ;  b,  into  three ;   x  350  (Kulliker  . 


Plexuses. — At  certain  parts  of  their  course,  nerves  form 
plexuses,  in  which  they  anastomose  with  each  other,  as  in  the  case 
of  the  brachial  and  lumbar  plexuses.  The  objects  of  such  inter- 
change of  fibres  are,  (a),  to  give  to  each  nerve  passing  off  from  the 
plexus,  a  wider  connection  with  the  spinal  cord  than  it  would  have 
if  it  proceeded  to  its  destination  without  such  communication  with 
other  nerves.  Thus,  each  nerve  by  the  wideness  of  its  connec- 
tions, is  less  dependent  on  the  integrity  of  any  single  portion,, 
whether  of  nerve-centre  or  of  nerve-trunk,  from  which  it  may 
spring.  (6)  Each  part  supplied  from  a  plexus  has  wider  relations 
with  the  nerve-centres,  and  more  extensive  sympathies  ;  and,  by 
means  of  the  same  arrangement,  groups  of  muscles  may  be  co- 
ordinated, every  member  of  the  group  receiving  motor  filaments 
from  the  same  parts  of  the  nerve-centre,  (c)  Any  given  part,  say 
a  limb,  is  less  dependent  upon  the  integrity  of  any  one  nerve. 
(d)  A  plexus  is  frequently  the  means  by  which  centripetal  and 
centrifugal  fibres  are  conveniently  mingled  for  distribution,  as  in 


chap,  xv m.]     PERIPHERAL   NERVE  TERMINATIONS 


547 


the  case  of  the  pneumogastric  nerve,  which  receives  motor  fila- 
ments, near  its  origin,  from  the  spinal  accessory. 

As   medullated   nerve-fibres  approach   their  terminations  they 

lose  their  medullary  sheath,  and  consist  then  merely  of  axis- 
cylinder  and  primitive  sheath.  They  then  lose  also  the  latter, 
and  only  the  axis-cylinder  is  left  with  here  and  there  a  nerve-cor- 
puscle partly  rolled  around  it.  Finally,  even  this  investment 
ceases,  and  the  axis-cylinder  breaks  up  into  its  elementary  fibrilhe. 


Peripheral  Nerve  Terminations. 
(a.)  Sensory. — (i.)  Pacinian  Corpuscles. — The  Pacinian  bodies 
or  corpuscles  (figs.  309  and  310),  named  after  their  discoverer 
Pacini,  are  little  elongated  oval  bodies, 
situated  on  some  of  the  cerebro-spinal 
and  sympathetic  nerves,  especially  the 
cutaneous  nerves  of  the  hands  and 
feet  ;  and  on  branches  of  the  large 
sympathetic  plexus  about  the  abdomi- 
nal aorta  (Kolliker).  They  often  occur 
also  on  the  nerves  of  the  mesentery, 
and  are  especially  well  seen  in  the 
mesentery  of  the  cat.  The}'  have  been 
observed  also  in  the  pancreas,  lympha- 
tic glands  and  thyroid  glands,  as  well 
as  in  the  penis  of  the  cat.  Each 
corpuscle  is  attached  by  a  narrow 
pedicle  to  the  nerve  on  which  it  is 
situated,  and  is  formed  of  several  con- 
centric layers  of  fine  membrane,  consist- 


ing of  a  hyaline  ground-membrane  with 


Fig.  309. — Extremities  of  a  nervr 
of  the  finger  with  Pacinian  cor- 
puscles attached,  about  the 
natural  size  (adapted  from 
Henle  and  Kolliker) . 


connective  tissue  fibres,  each  layer 
being  lined  by  endothelium  (fig.  310); 
through  its  pedicle  passes  a  single  nerve- 
fibre,  which,  after  traversing  the  several  concentric  layers  and  their 
immediate  spaces,  enters  a  central  cavity,  and,  gradually  losing  its 
dark  border,  and  becoming  smaller,  terminates  at  or  near  the 
distal  end  of  the  cavity,  in  a  knob-like  enlargement,  or  in  a  bifur- 
cation. The  enlargement  commonly  found  at  the  end  of  the  fibre, 
is  said   by   Pacini   to    resemble    a   ganglion    corpuscle ;  but  this 

N   N  2 


548 


THE  NEfiVOUS    SYSTEM. 


[CHAP.  XVIII 


observation  has  not  been  confirmed.     In  some  cases  two  nerves 
have  been  seen  entering  one  Pacinian  body,  and  in  others  a  nerve 

after  passing  unaltered  through 
one,  has  been  observed  to  termi- 
nate in  a  second  Pacinian  cor- 
puscle. The  physiological  import 
of  these  bodies  is  still  obscure. 
Closely  allied  to  Pacinian  cor- 
puscles, except  that  they  are 
smaller  and  longer,  with  a  row 
of  nuclei  around  the  central  ter- 
mination of  the  nerve  in  the 
core,  are  corpuscles  of  Herbst, 
which  have  been  found  chiefly 
in  the  tongues  of  ducks.  The 
capsules  are  nearer  together, 
and  towards  the  centre  the  en- 
dothelial sheath  appeal's  to  be 
absent. 

(2.)  End-hid  is  are  found  in  the 
conjunctiva,  in  the  penis  and 
clitoris,  in  the  skin,  and  in  ten- 
don ;  each  is  composed  of  a 
medullated  nerve -fibre  which 
terminates  in  corpuscles  of  vari- 
ous shapes,  with  a  capsule  con- 
taining a  transparent  or  striated 
mass,  in  the  centre  of  which 
terminates  the  axis-cylinder  of 
the   nerve-fibre,    the    ending   of 


Tig.  310. —  Parade  a.    corpuscle   of  th- 

mesent^ri/.  The  stalk  consists  of  a  nerve- 
libre  X)  with  its  thick  outer  sheath.  The 
peripheral  capsules  of  the  Pacinian  cor- 
puscle  are    continuous    with    the    outer 


sheath  of  the  stalk.    The  intermediary      which   IS   Somewhat  Clubbed  (tig. 
part   becomes  much  narrower  near  the  x 

230). 

(3.)  Touch  corpuscles  (fig.  229) 
are  found  in  the  papilla?  of  the 
skin  or  among  its  epithelium  ; 
they  maybe  simple  or  compound; 
when  simple  they  are  large  and 
slightly  flattened  transparent  nucleated  ganglion  cells  enclosed  in  a 
capsule ;  when  compound  the  capsule  contains  several  small  cells. 


entrance  of  the  axis-cylinder  into  the 
clear  central  mass.  A  hook-shaped  ter- 
mination with  the  end-bulb  T  i<  seen  in 
the  upper  part.  A  blood-vessel  V  enters 
the  Pacinian  corpuscle,  and  approaches 
the  end-bulb  ;  it  possesses  a  sheath  which 
is  the  continuation  of  the  peripheral  cap- 
sules of  the  Pacinian  corpuscle,  x  100. 
'Klein  and  Xoble  Smith.) 


chap,  xviii.]     PERIPHEEAL   NKltYK  TERMINATIONS. 


549 


The  corpuscles  of  Grandry  form  another  variety,  and  bare  been 
noticed  in  the  beaks  and  tongues  of  birds.  They  consist  of 
corpuscles  oval  or  Bpherical,  con- 
tained within  a  delicate  nucleated 
sheath,  and  containing  Beveral  cells. 
two  or  more  compressed  vertically. 
The  cells  are  granular  and  trans- 
parent, with  a  lindens.  The  nerve 
enters  on  one  side,  and  laying  aside 
its  medullary  sheath,  terminates  in 
or  between  the  cells. 

(4.)  In  plexuses,  as  in  the  cornea, 
both  sub-epithelial  and  also  intra- 
epithelial. 

(5.)  In  cells,  as  in  the  salivary 
glands  (p.  282),  and  in  the  special 
sense  organs.  To  the  latter,  further 
allusion  will  be  made  in  a  future 
chapter. 

(b.)  Motory — (1.)  In  unstriped 
muscle,  the  nerves  first  of  all  form 
a  plexus,  called  the  ground  plexus 
(Arnold),     corresponding    to    each 

group  of  muscle  bundles  ;  the  plexus  is  made  by  the  anasto- 
mosis of  the  primitive  fibrils  of  the  axis-cylinders.  From  the 
ground  plexus,  branches  pass  off,  and  again  anastomosing,  form 
plexuses  which  correspond  to  each  muscle  bundle, — intermedial'}/ 
plexuses.  From  these  plexuses  branches  consisting  of  primitive 
fibrils  pass  in  between  the  individual  fibres  and  anastomose. 
These  fibrils  either  send  off  finer  branches,  or  terminate  themselves 
in  the  nuclei  of  the  muscle  cells. 

(2.)  In  striped  muscle  the  nerves  end  in  the  so-called  "  motorud 
end-plates"  having  first  formed,  as  in  the  case  of  unstriped  fibres, 
ground  and  intermediary  plexuses.  The  nerves  are,  however, 
medullated,  and  when  a  branch  of  the  intermediary  plexus  passes 
to  enter  a  muscle-fibre,  its  primitive  sheath  becomes  continuous 
with  the  sarcolemma,  and  the  axis-cylinder  forms  a  network  of  its 
fibrils  on  the  surface  of  the  fibre.  This  network  lies  embedded  in 
a  flattened  granular  mass  containing  nuclei  of  several  kinds ;  this 


Fig.  311. — Summit  of  a  Pacinian  cor- 
puscle of  the  human  finger,  showing 
the  endothelial  membranes  lining 
the  capsules,  x  220.  (Klein  and 
Noble  Smith.) 


55o 


THE  NERVOUS   SYSTEM. 


[chap.  XVIII. 


is  the  motorial  end-plate  (fig.  312).  In  batrachia,  besides  end- 
plates,  there  is  another  way  in  which  the  nerves  end  in  the  muscle- 
fibres,  viz.,  by 
rounded  extremi- 
ties, to  which  ob- 
long nuclei  are 
attached. 

Nerve    Cells    or 
Corpuscles. 

The  vesicular 
nervous  substance 
contains,  as  its 
name  implies,  vesi- 
cles or  corpuscles, 
in  addition  to 
fibres;  and  a  struc- 
ture, thus  com. 
posed  of  corpuscles 
and  inter-commu- 
nicating fibres, 
constitutes  a  nerve- 
centre  ;  the  chief 
nerve-centres  be- 
ing the  srey  mat- 
ter  of  the  brain 
and  spinal  cord, 
and  the  various 
ganglia.  In  the 
brain  and  spinal 
cord  a  fine  stroma 
of  neuroglia  (p.  41),  extends  throughout  lx>th  the  fibrous  and 
vesicular  nervous  substance,  and  forms  a  supportiug  and  investing 
framework  for  the  whole. 

The  nerve-corpuscles  which  give  to  the  ganglia  and  to  certain 
parts  of  the  brain  and  spinal  cord  the  peculiar  greyish  or  reddish- 
grey  aspect  by  which  these  parts  are  characterised,  are  large, 
nucleated   cells,    filled  with   a  finely  granular  material,   some  of 


Fig.  312. — Two  striped  muscle-fibres  of  the  hyoglosstts  of  frog. 

a,  Nerve  end-plate  ;  h,  nerve  fibres  leaving  the  end-plate  ; 
«',  nerve-fibres,  terminating  after  dividing  into  brandies  ; 
d,  a  nucleu-  in  which  two  nerve-fibres  anastomose.  X  600. 
(Arndt.) 


CHAP.   Win.  ] 


NERVE   CORPUSC]  ES. 


551 


which   is  often   dark    like  pigment  :    the   nucleus  containing  a 

nucleolus.     Besides  varying  much  in  shape,  partly  in  consequence 

of  mutual  pressure,  they  present  Buch   other  varieties  as  make  it 

probable   cither  that    there   are 

two  different   kinds,  or  that,  in 

the  of  their  development, 

they  pass  through  very  different 

forms.      Some  of  them  are  small, 

general   spherical    or  ovoid,  and 

have     a     regular    uninterrupted 

outline.     These  simple  nerve-oor- 

puscles    are    most    numerous    in 

the  sympathetic  ganglia  ;  each  is 

enclosed   in   a   nucleated  sheath. 

Others,  which  are  called  caudate 

or   stellate     nerve-corpuscles     (tig. 

313),  are   larger,   and   have  one, 

t  wo,  or  more  long  processes  issuing 

from  them,  the  cells  being  called 

respectively    unipolar,  bipolar^  or 

multipolar;  which  processes  often 

divide  and  subdivide,  and  appear 

tubular,  and  tilled  with  the  same 

kind  of  granular  material  that  is 

contained   within    the   corpuscle. 

Of  these  processes  some   appear 

to  taper  to  a  point  and  terminate  at  a  greater  or  less  distance 

from   the    corpuscle ;    some  appear  to    anastomose    with   similar 

offsets  from  other  corpuscles  ;  while  others  are   continuous  with 

nerve-tibres,  the  prolongation  from  the  cell  by  degrees  assuming 

the  characters  of  the  nerve-fibre  with  which  it  is  continuous. 

Oanglion-cells  are  each  enclosed  in  a  transparent  membranous 
capsule  similar  in  appearance  to  the  nucleated  sheath  of  Schwann 
in  nerve-fibres  :  within  this  capsule  is  a  layer  of  small  flattened  cells. 

That  process  of  a  nerve-cell  which  becomes  continuous  with  a 
nerve-fibre  is  always  unbranched,  as  it  leaves  the  cell.  It  at  first 
has  all  the  characters  of  an  axis-cylinder,  but  soon  acquires  a 
medullary  sheath,  and  then  may  be  termed  a  nerve-fibre.  This 
continuity  of  nerve-cells  and  fibres  may  be  readily  traced  out  in 


Fipr.  313. —  Ganglion  nerve-corpuschj  of 
different  shapes.  (Klein  and  Noble 
Smith.) 


552  THE  NERVOUS  SYSTEM.  [( a  a  p.  xyiii. 

the    anterior  cornua   of   the    grey    matter    of  the    spinal    cord. 
In  many  large  branched  nerve-cells  a  distinctly  fibrillated  appear- 


Kg«  .\i}—An  isolated  sympathetic  ganglion  ceU  of  >,ia»,  showing  sheath  with  nucleated-eell 
lining,  B.  A.  Gang-lion-cell,  -with  nucleus  and  nucleolus.  C.  Branched  process.  I). 
Tnbranched  process.  Copied  from  Key  and  Retains.  X  7^0.  [Klein  and  Noble 
Smith). 

anceis  observable;  the  fibrillse  are  probably  continuous  with  those 
of  the  axis-cylinder  of  a  nerve. 


The  Functions  of  Nerve  Fibres. 

It  will  be  evident  from  the  account  of  nervous  action  previouslj 
given  (p.  513^  seq.)  that  nerve-fibres  arc  stimulated  to  act  by 
anything  which  increases  their  irritability,  but  that  they  are  in- 
capable of  originating  of  themselves  the  condition  necessary  for  the 
manifestation  of  their  own  functions.  When  a  cerebro-spinal  nerve- 
fibre  is  irritated  in  the  living  body  as  by  pinching,  or  by  heat,  or  by 
electrifying  it,  there  is,  under  ordinary  circumstances,  one  of  two 
effects, — either  there  is  pain,  or  there  is  twitching  of  one  or  more 
muscles  to  which  the  nerve  distributes  its  fibres.     From  various  con- 


<  bap.  win. 1  CONDUCTION    IN    m:i:\Ks.  $-> 

siderations  it  is  certain  that  pain  is  always  the  result  of  a  change 
in  the  nerve-cells  of  the  brain.  Therefore,  in  such  an  experiment  as 
that  referred  to,  the  irritat  ion  of  the  nerve-fibre  seems  to  1  he  experi- 
menter to  be  conducted  in  one  of  two  directions,  i.e.f  either  to  the 
brain  (central  termination  of  th>  fibre))  when  there  is  pain,  or  to  a 
muscle  (peripheral  termination)  when  there  is  movement. 

'The   effect  of  this   simple   experiment  is  a  type  of  what,  alv 

occurs  when  nerve  til >ivs  are  engaged  in  the  performance  of  their 
functions.  'The  result  of  Stimulating  them,  which  roughly  imitates 
what  happens  naturally  in  the  body,  IS  found  to  occur  at  one  or 
other  of  their  extremities,  central  or  peripheral,  never  at  both  ; 
and  in  accordance  with  this  fact,  and  because,  for  any  given  nerve- 
fibre,  the  result  is  always  the  same,  nerves  are  commonly  classed. 
as  sensory  or  motor. 

It  may  be  well  to  state,  in  order  to  avoid  confusion,  that  tlie  apparent 
conduction  in  both  directions,  which  seems  to  occur  when  a  nerve,  say  the 
ulnar  or  median  is  irritated,  depends  on  the  fad  thai  both  motor  and 
sensory  fibres  are  bound  up  together  in  the  same  nerve-trunks— wo.  arrange  - 
ment  which,  for  medium-sized  and  large  nerves,  is  the  rule  rather  than  the 
exception. 

Conduction  in  Nerves. — A  nerve  when  removed  from  the 
body  will  be  found  to  conduct  electrical  impressions  in  either 
direction  equally  well,  and  microscopic  examination  fails  to  dis- 
cover the  slightest  essential  difference  between  motor  and  sensory 
nerve-fibres.  The  question  therefore,  naturally  arises  whether  the 
conduction  of  a  stimulus  in  the  living  body,  in  one  direction  only,  is 
not  rather  apparent  than  real,  the  difference  in  the  result  being  due 
to  the  different  connections  of  the  two  kinds  of  nerve-fibres  respec- 
tively at  their  extremities.  In  other  words,  when  the  stimulation  of 
a  nerve-fibre  causes  pain,  the  result  is  due  to  its  central  extremity 
being  in  connection  with  structures  which  alone  can  give  rise  to 
the  sensation,  while  its  peripheral  extremity,  although  the  stimulus 
is  equally  conducted  to  it,  has  no  connection  with  a  structure 
which  can  respond  to  the  irritation  in  any  manner  sensible  to  the 
observer.  So,  when  motion  is  the  result  of  a  like  irritation,  it  is. 
because  the  peripheral  extremity  of  the  nerve-fibre  is  in  connection 
with  muscles  which  will  respond  by  contracting,  while  its  centra I 
extremity,  although  equally  stimulated,  has  no  means  of  showing 
the  fact  by  any  evident  result. 

That  this  is  the  true  explanation  is  made  highly  probable,  not 


IJ54  THE  NERVOUS   SYSTEM.  [chap.  xvur. 

merely  by  the  absence  of  any  structural  differences  in  the  two 

kinds  of  nerve-fibre,  but  also  by  the  fact,  proved  by  direct  experi- 
ment, that  if  a  centripetal  nerve  (gustatory)  be  divided,  and  its 
central  portion  be  made  to  unite  with  the  distal  portion  of  a 
divided  motor  nerve  (hypoglossal)  the  effect  of  irritating  the 
former  after  the  parts  have  healed,  is  to  excite  contraction  in  the 
muscles  supplied  by  the  latter.     (Philippeaux  and  Vulpian.) 

Classification  of  Nerve-Fibres. —  i.  Centripetal,  afferent,  or 
2.   Centrifugal,  afferent,  or  motor.      3.   Intercentral. 

Centripetal  or  afferent,  and  centrifugal  or  efferent  are  frequently 
employed  in  connection  with  nerve-fibres  in  lieu  of  the  corre- 
sponding terms  sensory  and  motor,  because  the  result  of  stimulat- 
ing a  nerve  of  the  former  kind  is  not  always  the  production  of 
pain  or  other  form  of  sensation,  nor  is  motion  the  invariable  result 
of  stimulating  the  latter. 

Conduction  in  centripetal  nerves  may  cause  (a)  pain,  or  some 
other  kind  of  sensation ;  or  (b)  reflex  action  ;  or  (c)  inhibition,  or 
restraint  of  action. 

Conduction  in  centrifugal  nerves  may  cause  (a)  contraction  of 
muscle  (p.  490),  (motor  nerves)  ;  or  {b)  it  may  influence  nutrition 
(trophic  nerves)  ;  or  (c)  may  influence  secretion  (secretory 
nerves). 

The  term  intercentral  is  applied  to  those  nerve-fibres  which 
connect  more  or  less  distinct  nerve-centres,  and  may,  therefore 
be  said  to  have  no  peripheral  distribution,  in  the  ordinary  sense  of 
the  term. 

It  is  a  law  of  action  in  all  nerve-fibres,  and  corresponds  with  the 
continuity  and  simplicity  of  their  course,  that  an  impression  made 
on  any  fibre,  is  simply  and  uninterruptedly  transmitted  along  it, 
without  being  imparted  or  diffused  to  any  of  the  fibres  lying  near 
it.  In  other  words,  all  nerve-fibres  are  mere  conductors  of  impres- 
sions. Their  adaptation  to  this  purpose  is,  perhaps,  due  to  the 
contents  of  each  fibre  being  completely  isolated  from  those  of 
adjacent  fibres  by  the  membrane  or  sheath  in  which  each  is 
enclosed,  and  which  acts,  it  may  be  supposed,  just  as  silk,  or  other 
non-conductors  of  electricity  do,  which,  when  covering  a  wire, 
prevent  the  electric  condition  of  the  wire  from  being  conducted 
into  the  surrounding  medium. 

Velocity  of  Nerve-force.  —  The  change    which    a   stimulus 


chap,  xviii.]  CONDUCTION    IN    SERVES.  555 

sets   upon   a   licrvr,  of  the  exact   nature   of  which    we   are  un- 
acquainted, appears  to  travel   along  a  nerve-fibre  in  both  direc 
tione  in  the  form  of  a  wave     Nervous  force  travels  along  nerve- 
fibres   with    considerable    velocity.       Eelmholtz   and   Baxt   have 

bimated  the  average  rate  of  conduction  in  human  motor  nerves 
at  tii  feet  (nearly  29  metres)  per  second;  this  result  agreeing 
very  closely  with  that  previously  obtained  by  Hirsch.  Ruther- 
ford's observations  agree  with  those  of  Von  Wittich,  that 
the  rate  of  transmission  in  sensory  nerves  is  about  140  feet  per 
ml. 

Conduction  in  Sensory  Nerves.  Centripetal  nerves  appear 
(p.  553)  able  to  convey  impressions  only  from  the  parts  in  which 
they  are  distributed,  towards  the  nerve-centre  from  which  they 
arise,  or  to  which  they  tend.  Thus,  when  a  sensitive  nerve  is 
divided,  and  irritation  is  applied  to  the  end  of  the  proximal 
portion,  i.e.,  of  the  portion  still  connected  with  the  nervous  centre, 
sensation  is  perceived,  or  a  reflex  action  ensues  ;  but,  when  the 
end  of  the  distal  portion  of  the  divided  nerve  is  irritated,  no  effect 
appears.  When  an  impression  is  made  upon  any  part  of  the 
course  of  a  sensory  nerve,  the  mind  may  perceive  it  as  if  it  were 
made  not  only  upon  the  point  to  which  the  stimulus  is  applied, 
but  also  upon  all  the  points  in  which  the  fibres  of  the  irritated 
nerve  are  distributed  :  in  other  words,  the  effect  is  the  same  as  if 
the  irritation  were  applied  to  the  parts  supplied  by  the  branches 
of  the  nerve.  When  the  whole  trunk  of  the  nerve  is  irritated,  the 
sensation  is  felt  at  all  the  parts  which  receive  branches  from  it ; 
but  when  only  individual  portions  of  the  trunk  are  irritated,  the 
sensation  is  perceived  at  those  parts  only  which  are  supplied  by 
the  several  portions.  Thus,  if  we  compress  the  ulnar  nerve 
where  it  lies  at  the  inner  side  of  the  elbow-joint,  behind  the 
internal  condyle,  we  have  the  sensation  of  "  pins  and  needles," 
<>r  of  a  shock,  in  the  parts  to  which  its  fibres  are  distributed, 
namely,  in  the  palm  and  back  of  the  hand,  and  in  the  lifth  and 
ulna  half  of  the  fourth  finger.  When  stronger  pressure  is  made, 
the  sensations  are  felt  in  the  fore-arm  also  ;  and  if  the  mode  and 
direction  of  the  pressure  be  varied,  the  sensation  is  felt  by  turns 
in  the  fourth  finger,  in  the  fifth,  and  in  the  palm  of  the  hand, 
or  in  the  back  of  the  hand,  according  as  different  fibres  or  fasciculi 
of  fibres  are  more  pressed  upon  than  others. 


556  THE  XEB  VOL'S   SYSTEM.  [chap,  xviit. 

Illustrations. — It  is  in  accordance  with  this  law,  that  when  parts  are 
deprived  of  sensibility  by  compression  or  division  of  the  nerves  supplying 
them,  irritation  of  the  portion  of  the  nerve  connected  with  the  brain  still 
excites  sensations  which  are  felt  as  if  derived  from  the  parts  to  which  the 
peripheral  extremities  of  the  nerve-fibres  are  distributed.  Thus,  there  are 
cases  of  paralysis  in  which  the  limbs  are  totally  insensible  to  external  stimuli, 
yet  are  the  seat  of  most  violent  pain,  resulting  apparently  from  irritation 
of  the  sound  part  of  the  trunk  of  the  nerve  still  in  connection  with  the 
brain,  or  from  irritation  of  those  parts  of  the  nervous  centre  from  which 
the  sensory  nerve  or  nerves  which  supply  the  paralysed  limbs  originate.  An 
illustration  of  the  same  law  is  also  afforded  by  the  cases  in  which  division  of 
a  nerve  for  the  cure  of  neuralgic  pain  is  found  useless,  and  in  which  the 
pain  continues  or  returns,  though  portions  of  the  nerves  be  removed.  In 
such  cases,  the  disease  is  probably  seated  nearer  the  nervous  centre  than  the 
part  at  which  the  division  of  the  nerve  is  made,  or  it  may  be  in  the  nervous 
centre  itself.  In  the  same  way  may  be  explained  the  fact,  that  when  part 
of  a  limb  has  been  removed  by  amputation,  the  remaining  portions  of  the 
nerves  may  give  rise  to  sensations  which  the  mind  refers  to  the  lost  parr. 
When  the  stump  is  healed,  the  sensations  which  we  are  accustomed  to  have 
in  a  sound  limb  are  still  felt ;  and  tingling  and  pains  are  referred  to  the 
parts  that  are  lost,  or  to  particular  portions  of  them,  as  to  single  to  3,  t  i 
the  sole  of  the  foot,  to  the  dorsum  of  the  foot,  etc. 

It  must  not  be  assumed,  as  it  often  lias  been,  that  the  mind 
has  no  power  of  discriminating  the  very  point  in  the  length  of 
any  nerve-fibre  to  which  an  irritation  is  applied.  Even  in  the 
instances  referred  to,  the  mind  perceives  the  pressure  of  a  nerve 
at  the  point  of  pressure,  as  well  as  in  the  seeming  sensations 
derived  from  the  extremities  of  the  fibres  :  and  in  stumps,  pain  is 
felt  in  the  stump,  as  well  as,  seemingly,  in  the  parts  removed. 
It  is  not  quite  certain  whether  those  sensations  are  due  to  con- 
duction through  the  nerve  fibres  which  are  on  their  way  to  be 
distributed  elsewhere,  or  through  the  sentient  extremities  of 
nerves  which  are  themselves  distributed  to  the  many  trunks  of 
the  nerves,  the  nervi  nervorum.  The  latter  is  the  more  probable 
supposition. 

When,  in  a  part  of  the  body  which  receives  two  sensory  nerves,, 
one  is  paralysed,  the  other  may  or  may  not  be  inadequate  to 
maintain  the  sensibility  of  the  entire  part ;  the  extent  to  which 
the  sensibility  is  preserved  corresponding  probably  with  the 
number  of  the  fibres  unaffected  by  the  paralysis.  There  are- 
instances  in  which  the  trunk  of  the  chief  sensory  nerve  supplied 
to  a  part  having  been  divided,  the  sensibility  of  the  part  is  still 
preserved  by  intercommunicating  fibres  from  a  neighbouring 
nerve-trunk. 


chap,  xvn r.]  CONDUCTION   IN    NERVES.  rry 

Conduction  in  the  Nerves  of  Special  Sense. The  laws 

of  conduction  in  the  olfactory,  optic,  auditory,  <j>i*i<itory — resemble 
in  many  aspects  those  of  conduction  in  the  nerves  of  common  sen- 
sation, just  described.  Tims  the  effect  is  always  central ;  stimula- 
tion of  the  trunk  of  the  nerve  produces  the  same  effect  as  that  of 
its  extremities,  and  if  the  nerve  be  severed,  it  is  the  central  and 
not  the  peripheral  extremity  which  responds  to  irritation,  although 
the  sensation  is  referred  to  the  periphery.  There  are,  however, 
certain  peculiarities  in  the  effects.  Thus  the  various  stimuli 
which  might  cause,  through  an  ordinary  sensitive  nerve,  the  sense 
of  pain,  would,  if  applied  to  the  optic  nerve,  cause  a  sensation  as 
of  flashes  of  light;  if  applied  to  the  olfactory,  there  would  he  a 
.-ense  as  of  something  smelt.     And  so  with  the  other  two. 

Hence  the  explanation  of  so-called  suhjective  sensations.  Irri- 
tation in  the  optic  nerve,  or  the  part  of  the  brain  from  which  it 
arises,  may  cause  a  patient  to  believe  he  sees  flashes  of  li^ht, 
and  among  the  commonest  troubles  of  the  nerves  of  special  sense, 
is  the  distressing  noise  in  the  head  (tinnitus  aurium),  which 
depends  on  some  unknown  stimulation  of  the  auditory  nerve  or 
centre  quite  unconnected  with  external  sounds. 

Conduction  in  Motor  Nerves. — Conduction  in  motor  nerves 
presents  a  remarkable  contrast  with  the  foregoing.  Thus — the 
effect  of  applying  a  stimulus  to  the  motor  nerve  is  always  notice- 
able, at  the  peripheral  extremity,  in  the  contraction  of  muscles 
supplied  by  it.  If  a  motor  nerve  be  severed,  irritation  of  the 
distal  portion  causes  contraction  of  muscle,  but  no  effect  whatever 
is  produced  by  stimulating  that  part  of  the  nerve  which  is  still 
in  direct  connection  with  the  nerve-centre. 

Contractions  are  excited  in  all  the  muscles  supplied  by  the 
branches  given  off  by  the  nerve  below  the  point  irritated,  and  in 
those  muscles  alone  :  the  muscles  supplied  by  the  branches  which 
come  off  from  the  nerve  at  a  higher  point  than  that  irritated,  are 
not  directly  excited  to  contraction.  And  it  is  from  the  same  fact 
that,  when  a  motor  nerve  enters  a  plexus  and  contributes  with 
•other  nerves  to  the  formation  of  a  nervous  trunk  proceeding  from 
the  plexus,  it  does  not  impart  motor  power  to  the  whole  of  that 
trunk,  but  only  retains  it  isolated  in  the  fibres  which  form  its 
continuation  in  the  branches  of  that  trunk. 


558  THE  NERVOUS   SYSTEM.  [chap,  xviii. 

Functions  of  Nerve-Centres. 
The  functions  of  nerve-centres  may  be  classified  as  follows: — 
i.    Conduction.      2.    Transference.     3.   Reflection.     4.   Automatism. 
5.  Augmentation.     6.   Inhibition. 

1.  Conduction. — Conduction  in  or  through  nerve-centres  may 
be  thus  simply  illustrated.  The  food  in  a  given  portion  of  the 
intestines,  acting  as  a  stimulus,  produces  a  certain  impression  on 
the  nerves  in  the  mucous  membrane,  which  impression  is  conveyed 
through  them  to  the  adjacent  ganglia  of  the  sympathetic.  In 
ordinary  cases,  the  consequence  of  such  an  impression  on  the 
ganglia  is  the  movement  by  reflex  action  (p.  560)  of  the  muscular 
coat  of  that  and  the  adjacent  part  of  the  canal.  But.  if  irritant 
substances  be  mingled  with  the  food,  the  sharper  stimulus  pro- 
duces a  stronger  impression,  and  this  is  conducted  through  the 
nearest  ganglia  to  others  more  and  more  distant ;  and,  from  all 
these,  reflex  motor  impulses  issuing,  excite  a  wide-extended  and 
more  forcible  action  of  the  intestines.  Or  even  through  the 
sympathetic  ganglia,  the  impression  may  lie  further  conducted  to 
the  ganglia  of  the  spinal  nerves,  and  through  them  to  the  spinal 
cord,  whence  may  issue  motor  impulses  to  the  abdominal  and  other 
muscles,  producing  cramp.  And  yet  further,  the  same  morbid 
impression  may  be  conducted  through  the  spinal  cord  to  the  brain, 
where  it  may  be  felt.  In  the  opposite  direction,  mental  influence 
may  be  conducted  from  the  brain  through  a  succession  of  nervous 
centres— the  spinal  cord  and  ganglia,  and  one  or  more  ganglia 
of  the  sympathetic — to  produce  the  influence  of  the  mind  on  the 
digestive  and  other  organs  ;  altering  both  the  quantity  and  quality 
of  their  secretions. 

2.  Transference. — It  lias  been  previously  stated  that  impres- 
sions conveyed  by  any  centripetal  nerve-fibre  travel  uninterruptedly 
throughout  its  whole  length,  and  are  not  communicated  to  adjacent 

fibres. 

When  such  an  impression,  however,  reaches  a  nerve-centre,  it 
may  seem  to  be  communicated  to  another  fibre  or  fibres;  as  pain 
or  some  other  kind  of  sensation  may  be  felt  in  a  part  different 
altogether  from  that  from  which,  so  to  speak,  the  stimulus  started. 
Thus,  in  disease  of  the  hip,  there  may  be  pain  in  the  knee.  This 
apparent  change  of  place  of  a  sensation  to  a  part  to  which  it  would 
not  seem  properly  to  belong  is  termed  transference. 


chap,  xviii.]        FUNCTIONS   OF   NERVE-CENTRES.  559 

The  transference  of  impressions  may  be  illustrated  by  the  fact 
just  referred  to,   -the  pain  in  the  knee,  which  is  a  common  sign  of 
disease  of  the   hip.     In  this   ease  the   impression  made  by  the 
disease  on  the  nerves  of  the  hip-joint  is  conveyed  to  the  spinal 
cord  ;  there  it  is  transferred  to  the  central  ends  or  connections  of 
the  nerve-fibres  which  are  distributed  about  the  knee.     Through 
these  the  transferred    impression  is  conducted  to  the  brain,  which, 
referring  the  sensation  to  the  part  from  which  it  usually  through 
these    fibres    receives  impressions,  feels    as  if  the   disease   and  the 
source  of  pain  were  in  the  knee.     At  the  same  time  that  it  is  trans- 
ferred, the  jH'imary  impression  maybe  also  conducted  to  the  brain  : 
and  in  this  case   the  pain  is  felt  in  both  the    hip  and  the   knee. 
And  s<»,  in  whatever   part  of  the  respiratory  organs  an  irritation 
may  be  seated,  the  impression  it  produces,  being-  conducted  to  the 
medulla  oblongata,  is  transferred  to  the  central  connections  of  the 
nerves  of  the  larynx  :  and  thence,  being  conducted  as  in  the  last 
case    to  the  brain,  the  latter   perceives  the  peculiar  sensation   of 
tickling  in  the  glottis,  which   excites   the  act  of  coughing.     Or. 
again,  when  the  sun's  light   falls  strongly  on  the  eye,  a  tickling- 
may  be  felt  in  the  nose,  exciting  sneezing. 

A  variety  of  transference,  which  may  be  termed  radiation  of 
impressions,  is  shown  when  an  impression  received  by  a  nervous 
eentre  is  diffused  to  many  other  parts  in  the  same  centre,  and 
produces  sensations  extending  for  beyond  the  part  from  which  the 
primary  impression  was  derived.  Hence,  as  in  the  former  ca>-  s, 
result  various  kinds  of  what  have  been  denominated  sympathetic 
sensations.  Sometimes  such  sensations  are  referred  to  almost 
every  part  of  the  body  :  as  in  the  shock  and  tingling  of  the  skin 
produced  by  some  startling  noise.  Sometimes  only  the  parts 
immediately  surrounding  the  point  first  irritated  participate  in 
the  effects  of  the  irritation;  thus,  the  aching  of  a  tooth  may  be 
accompanied  by  pain  in  the  adjoining  teeth,  and  in  all  the  sur- 
rounding parts  of  the  face  ;  the  explanation  of  such  a  case  being, 
that  the  irritation  conveyed  to  the  brain  by  the  nerve-fibres  of  the 
diseased  tooth  is  radiated  to  the  central  ends  of  adjoining  fibres. 
and  that  the  mind  perceives  this  secondary  impression  as  if  it  were 
derived  from  the  peripheral  ends  of  the  fibres. 

3.  Keflection. — In  the  cases  of  transference  of  nerve-force  just 
described,  it  has  been  said  that  all  that  need  be  assumed  is  a  com- 


560  THE  NEKYOUS   SYSTEM.  [chap.  xvnr. 

munication  of  tlie  excited,  condition  of  an  afferent  nerve  to  other 
parte  of  its  nerve-centre  than  that  from  which  it  takes  its  origin. 
In  the  case  of  reflection,  on  the  other  hand,  the  stimulus  having 
been  conveyed  to  a  nerve-centre  by  a  centripetal  nerve,  is  con- 
ducted away  again  by  a  centrifugal  nerve,  and  effects  some  change 
- — motor,  secretory  or  nutritive,  at  the  peripheral  extremity  of  the 
latter — the  difference  in  effect  depending  on  the  variety  of  centri- 
fugal nerve  secondarily  affected.  As  in  transference,  the  reflect  ion 
may  take  place  from  a  certain  limited  set  of  centripetal  nerves  to 
a  corresponding  and  related  set  of  centrifugal  nerves  :  as  when  in 
•consequence  of  the  impression  of  light  on  the  retina,  the  iris  con- 
tracts, but  no  other  muscle  moves.  Or  the  reflection  may  extend 
to  widely  different  parts:  as  when  an  irritation  in  the  larynx 
brings  all  the  muscles  engaged  in  expiration  into  coincident 
movement.  Reflex  movements,  occurring  quite  independently  of 
sensation,  are  generally  called  excito-wiotor  :  those  which  are  guided 
or  accompanied  by  sensation,  but  not  to  the  extent  of  a  distinct 
perception  or  intellectual  process  are  termed  sensors-motor. 

Laws  of  reflex  action. — (")  For  the  manifestation  of  every 
reflex  action,  these  things  are  necessary  :  (1),  one  or  more  perfect 
centripetal  nerve-fibres,  to  convey  an  impression  ;  (2),  a  nervous 
centre  for  its  reception,  and  by  which  it  may  be  reflected;  (3),  one 
■or  more  centrifugal  nerve-fibres,  along  which  the  impression  may 
be  conducted  to  (4),  the  muscular  or  other  tissue  by  which  the 
•effect  is  manifested  (p.  554).  In  the  absence  of  any  one  of  these 
•conditions,  a  proper  reflex  action  could  not  take  place  :  and  when- 
ever, for  example,  impressions  made  by  external  stimuli  on  sensory 
nerves  give  rise  to  motions,  these  are  never  the  result  of  the  direct 
reaction  of  the  sensory  and  motor  fibres  of  the  nerves  on  each 
•<  ither  ;  in  all  such  eases  the  impression  is  conveyed  by  the  afferent 
fibres  to  a  nerve-centre,  and  is  therein  communicated  to  the  motor 
fibres. 

(b)  All  reflex  actions  are  essentially  involuntary,  though  most 
of  them  admit  of  being  modified,  controlled,  or  prevented  by  a 
voluntary  effort. 

(c)  Reflex  actions  performed  in  health  have,  for  the  most  part, 
a  distinct  purpose,  and  are  adapted  to  secure  some  end  desirable 
for  the  well-being  of  the  body  ;  but,  in  disease,  many  of  them  are 
irregular  and  purposeless.     As  an  illustration  of  the  first  po:nt, 


<-hap.  win.]  REFLEX   ACTION.     ■  561 

may  be  mentioned  movements  of  the  digestive  canal,  tin.'  respira- 
tory movements,  and  the  contraction  of  the  eyelids  and  the  pupil 
to  exclude  many  rays  of  Light,  when  the  retina  is  exposed  to  a 
bright  glare.  These  and  all  other  normal  reflex  acts  afford  also 
examples  of  the  mode  in  which  the  nervous  centres  combine  and 
arrange  co-ordinately  the  actions  of  the  nerve-fibres,  so  that  many 
muscles  may  act  together  for  the  common  end.  Another  instance 
<>f  the  same  kind  furnished  by  the  spasmodic  contractions  of  the 
glottis  on  the  contact  of  carbonic  acid,  or  any  foreign  substance, 
with  the  surface  of  the  epiglottis  or  larynx.  Examples  of  the 
purposeless  irregular  nature  of  morbid  reflex  action  are  seen  in  the 
convulsive  movements  of  epilepsy,  and  in  the  spasms  of  tetanus 
and  hydrophobia. 

(</)  Reflex  muscular  acts  arc  often  more  sustained  than  those 
produced  by  the  direct  stimulus  of  muscular  nerves.  The  irrita- 
tion of  a  muscular  organ,  or  its  motor  nerve,  produces  contraction 
lasting  only  so  long  as  the  irritation  continues  ;  but  irritation 
applied  to  a  nervous  centre  through  one  of  its  centripetal  nerves, 
may  excite  reflex  and  harmonious  contractions,  which,  last  some 
time  after  the  withdrawal  of  the  stimulus  (Volkmann). 

Classification  of  Reflex  Actions. — Keflex  actions  may  be 
classified  as  follows  (Kuss) : — 1.  Those  in  which  both  the  centri- 
petal and  centrifugal  nerves  concerned  are  cerebrospinal ;  e.g., 
deglutition,  sneezing,  coughing,  and,  in  pathological  conditions, 
tetanus,  epilepsy.  2.  Those  in  which  the  centripetal  nerve  is 
cerebrospinal,  and  the  centrifugal  is  sympatlietic,  most  often  vaso- 
motor ;  e.g.,  secretion  of  saliva,  or  gastric  juice  ;  blushing  or  pallor 
of  the  skin.  3.  Those  in  which  the  centripetal  nerve  is  of  the 
sympathetic  system,  and  the  centrifugal  is  cerebrospinal.  The 
majority  of  these  are  pathological,  as  in  the  case  of  convulsions 
produced  by  intestinal  worms,  or  hysterical  convulsions.  4.  Those 
in  which  both  centripetal  and  centrifugal  nerves  are  of  the 
sympathetic  system:  as,  fur  example,  the  obscure  actions  which 
preside  over  the  secretion  of  the  intestinal  fluids,  those  which  unite 
the  various  generative  functions  and  many  pathological  phenomena. 
Relations  between  the  Stimulus  and  the  Resulting  Reflex 
Action. — Certain  rules  showing  the  relation  between  the  result- 
ing reflex  action  and  the  stimulus  have  been  drawn  up  by  Pfliiger, 
as  follows  : — 

0  0 


562  THE  NERVOUS   SYSTEM.  [chap,  xviii. 

1.  Law  of  unilateral  reflection. — A  slight  irritation  of  sensory 
nerves  is  reflected  along  the  motor  nerves  of  the  same  region. 
Thus,  if  the  skin  of  a  frog's  foot  be  tickled  on  the  right  side,  the 
right  leg  is  drawn  up. 

2.  Laiv  of  symmetrical  rejection. — A  stronger  irritation  is  reflected, 
not  only  on  one  side,  but  also  along  the  corresponding  motor  nerves 
of  the  opposite  side.  Thus,  if  the  spinal  cord  of  a  man  has  been 
severed  by  a  stab  in  the  back,  when  one  foot  is  tickled  both  legs  will 
be  drawn  up. 

3.  Law  of  intensity. — In  the  above  case,  the  contractions  will  be 
more  violent  on  the  side  irritated. 

4.  Law  of  radiation. — If  the  irritation  (afferent  impulse)  in- 
creases, it  is  reflected  along  the  motor  nerves  which  spring  from 
points  higher  up  the  spinal  cord,  till  at  length  all  the  muscles  of 
the  body  are  thrown  into  action. 

Simple  and  Co-ordinated  Reflex  Actions. — In  the  simplest 
form  of  reflex  action  a  single  nerve  cell  with  an  afferent  and  an 
efferent  fibre  is  concerned,  but  in  the  majority  of  actual  actions 
a  number  of  cells  are  probably  concerned,  and  the  impression  is  as 
it  were  distributed  among  them,  and  they  act  in  concert  or  co- 
ordination.    This  co-ordinating  power  belongs  to  nerve  centres. 

Primary  and  Secondary  or  acquired  reflex  actions. — 
We  must  carefully  distinguish  between  such  reflex  actions  which  may 
be  termed  primary,  and  those  which  are  secondary  or  acquired.  As 
examples,  of  the  former  class  we  may  cite  sucking,  contraction  of 
the  pupil,  drawing  up  the  legs  when  the  toes  are  tickled,  and  many 
others  which  are  performed  as  perfectly  by  the  infant  as  by  the  adult. 

The  large  class  of  secondary  reflex  actions  consists  of  acts  which 
require  for  their  first  performance  and  many  subsequent  repetitions 
an  effort  of  will,  but  which  by  constant  repetition  are  habitually 
though  not  necessarily  performed,  mechanically,  i.e.,  without  the 
intervention  of  consciousness  and  volition.  As  instances  we  may 
take  reading,  writing,  walking,  &c. 

In  endeavouring  to  conceive  how  such  complicated  actions  can 
be  performed  without  consciousness  and  will,  we  must  suppose  that 
in  the  first  instance  the  will  directs  the  nerve-force  along  certain 
channels  causing  the  performance  of  certain  acts,  e.g.,  the  various 
movements  of  flexion  and  extension  involved  in  walking.  After  a 
time  by  constant  repetition,  these  routes  become,  to  use  a  metaphor. 


(MAP.  xviii.]  AUTOMATISM.  563 

well  worn:  then'  is,  as  it  were,  a  beaten  track  along  which  the 
nerve-force  travels  with  much  greater  case  than  formerly:  bo 
much  so  that  a  Blight  stimulus  such  as  the  pressure  of  the  foot  on 
the  ground,  is  sufficient  to  start  and  keep  going  indefinitely  the 
complex  reflex  actions  of  walking  during  entire  mental  abstraction, 
or  even  during  sleep.  In  such  acts  as  reading,  writing,  and  the 
like,  it  would  appear  as  if  the  will  set  the  necessary  reflex 
machinery  going,  and  that  the  reflex  actions  go  on  uninterruptedly 
until  again  interfered  with  by  the  will. 

Without  this  capacity  possessed  by  the  nervous  system  of 
"organising  conscious  actions  into  more  or  less  unconscious  ones," 
education  or  training  Avould  be  impossible.  A  most  important 
part  of  the  process  by  which  these  acquired  reflex  actions  come 
to  be  performed  automatically  consists  in  what  is  termed  associa- 
tion. If  two  acts  be  at  first  performed  voluntarily  in  succession, 
and  this  succession  is  often  repeated,  the  performance  of  the  first 
is  at  once  followed  mechanically  by  the  second.  Instances  of  this 
"  force  of  habit "  must  be  within  the  daily  experience  of  every  one. 

Of  course  it  is  only  such  actions  as  have  become  entirely  reflex 
that  can  be  performed  during  complete  unconsciousness,  as  in 
sleep.  Cases  of  somnambulism  are  of  course  familiar  to  every  one, 
and  authentic  instances  are  on  record  of  persons  writing  and  even 
playing  the  piano  during  sleep. 

4.  Automatism. — To  nerve  centres,  it  is  said,  belongs  the 
property  of  originating  nerve-impulses,  as  well  as  of  receiving  them 
and  conducting  and  reflecting  them. 

The  term  automatism  is  employed  to  indicate  the  origination  of 
nervous  impulses  in  nerve-centres,  and  their  conduction  therefrom, 
independently  of  previous  reception  of  a  stimulus  from  another 
part.  It  is  impossible,  in  the  present  state  of  our  knowledge,  to 
say  definitely  what  actions  in  the  body  are  really  in  this  sense 
automatic.  An  example  of  automatic  nerve-action  has  been 
already  referred  to,  i.e.,  that  of  the  respirator}'  centre,  but  the 
apparently  best  examples  of  automatism  are  found,  however,  in 
the  case  of  the  cerebrum,  which  will  be  presently  considered. 

5.  and  6.  Augmentation  and  Inhibition. — Nerve  cells  not 
only  receive  and  reflect  nerve  impulses,  and  also  in  some  cases  even 
originate  such  impulses,  but  they  are  also  capable  of  increasing 
the  impulse,  and  the  result  is  what  is  called  augmentation;  and 

o  o  2 


04  THE  NERVOUS   SYSTEM.  [chap.  xvnr. 

when  a  nerve  centre  is  in  action  its  action  is  also  capable  of  being 
increased  or  diminished  (inhibition)  by  afferent  impulses.  This 
is  the  case  in  whatever  way  the  centre  has  caused  the  action, 
whether  of  itself  or  by  means  of  previous  afferent  impulses.  The 
action,  by  which  a  centre  is  capable  of  being  inhibited  or  exalted, 
has  been  well  shewn  in  the  case  of  the  vaso-motor  centre,  before 
described  (p.  193).  This  power,  which  can  be  exerted  from  the 
periphery,  is  very  important  in  regulating  the  action  even  of 
partially  automatic  centres  such  as  the  respiratory  centre. 

Cerebro-spinal  Nervous  System. 

The  physiology  of  the  cerebro-spinal  nervous  system  includes  that 
of  the  Spinal  Cord,  Medulla  Oblongata,  and  Brain,  of  the  several 
ISTerves  given  off  from  each,  and  of  the  Ganglia  on  those  nerves. 

Membranes  of  the  Brain  and  Spinal  Cord. — The  Brain 
and  Spinal  Cord  are  enveloped  in  three  membranes — (1)  the  Dura 
Mater,  (2)  the  Arachnoid,  (3)  the  Pia  Mater. 

(1.)  The  Dura  Mater,  or  external  covering,  is  a  tough  mem- 
brane composed  of  bundles  of  connective  tissue  which  cross  at 
various  angles,  and  in  whose  interstices  branched  connective- 
tissue  corpuscles  lie  :  it  is  lined  by  a  thin  elastic  membrane,  and 
on  the  inner  surface,  and,  where  it  is  not  adherent  to  the  bone,  on 
the  outer  surface  also  is  a  layer  of  endothelial  cells  very  similar  to 
those  found  in  serous  membranes.  (2.)  The  Arachnoid  is  a  much 
more  delicate  membrane  very  similar  in  structure  to  the  dura 
mater,  and  lined  on  its  outer  or  free  surface  by  an  endothelial  mem- 
brane. (3.)  The  Pia  Mater  consists  of  two  chief  layers,  between 
which  numerous  blood-vessels  ramify.  Between  the  arachnoid  and 
pia  mater  is  a  network  of  fibrous-tissue  trabecule  sheathed  witli 
endothelial  cells  :  these  sub-arachnoid  trabecule  divide  up  the  sub- 
arachnoid space  into  a  number  of  irregular  sinuses.  There  are 
some  similar  trabecule,  but  much  fewer  in  number,  traversing  the 
sub-dural  space,  i.e.,  the  space  between  the  dura  mater  and  arachnoid. 
"  Pacchionian  bodies"  are  growths  from  the  sub-arachnoid  net- 
work of  connective-tissue  trabecule  which  project  through  small 
holes  in  the  inner  layers  of  the  dura  mater  into  the  venous  sinuses 
of  that  membrane.  The  venous  sinuses  of  the  dura  mater  have 
been  injected  from  the  Bub-arachnoidal  space  through  the  interme- 
diation of  these  villous  outgrowths  known  as  "  Pacchionian  bodies.' 


OB  \r.  win.] 


CEKKUIin-SPINAI,   SYSTEM. 


56S 


Tho  Spinal  Cord  and  its  Nerves. 

The  Spinal  cord  is  a  cylindriform  column  of  nerve-substance  con- 
nected above  with  the 
brain  through  the 
medium  of  the  me- 
dulla oblongata,  and 
terminating  below, 
about  the  lower  bor- 
der of  the  first  lumbar 
vertebra,  in  a  Blender 
filament  of  grey  sub- 
stance, the  Jilum  ter- 


minate, which  lies  in 
the  midst  of  the  roots 
of  many  nerves  form- 
ing the  cauda  equina. 
Structure. —  The 
cord  is  composed  of 
white  and  grey  ner- 
vous substance,  of 
which  the  former  is 
situated  externally, 
and  constitutes  its 
chief  portion,  while 
the  latter  occupies  its 
central  or  axial  por- 
tion, and  is  so  ar- 
ranged,      that       on 


Carebruiifl 


'ont  V8f;*fl?«V-vA 
Mr  dull  Oblony\~ 


Vfiftjer  Extrtrnity 
of  S/tavzl  Cord 


Vertebra, 


Lowev  Extremity  -  -\  -^3 
of  Sfiinal  Cord         I    g 


— V — 1st  Lumbar 

^A  Vertebra 


Coccyx 


Fig.  315. —  View  of  the  cerebro- 
spinal axis  of  the  nervous 
system.  The  right  half  of 
the  cranium  and  trunk  of 
the  body  has  been  removed 
by  a  vertical  section ;  the 
membranes  of  the  brain 
and  spinal  marrow  have 
also  been  removed,  and  the 
roots  and  first  part  of  the 
fifth  and  ninth  cranial,  and 
of  all  the  spinal  nerves  <>f 
the  right  side,  have  been 
dissected  out  and  laid  sepa- 
rately on  the  wall  of  the  ekuU  and  on  the  several  vertebra?  opposite  to  the  place  -pf 
their  natural  exit  from  the  cranio-spinal  cavity.     (After  Bourgery.) 


566 


THE  NERVOUS   SYSTEM. 


[chap.  XVIII. 


the  surface  of  a  transverse  section  of  the  cord  it  appears 
like  two  somewhat  crescentic  masses  connected  together  by 
a  narrower  portion  or  isthmus  (fig.  318).  Passing  through 
the  centre  of  this  isthmus  in  a  longitudinal  direction  is 
a  minute  canal  (central  canal),  which  is  continued  through  the 
whole  length  of  the  cord,  and  opens  above  into  the  space  at  the 

back  of  medulla 
*  — 2 — -  oblongata    and 

pons  Varolii, 
called  the 
fourth  ventri- 
cle. It  is  lined 
by  a  layer  of 
columnar  cili- 
ated epithe- 
lium. 

The  spinal 
cord  consists  of 
two  exactly 
symmetrical 
halves  separa- 
ted anteriorly 
and  posteriorly 
by  vertical  jis- 
sures  (the  pos- 
terior fissure 
being  deeper, 
but  less  wide 
and  distinct 
than  the  ante- 
rior), and  uni- 
ted in  the  mid- 
dle by  nervous 
matter  which  is 

usually  described  as  forming  two  commissures — an  anterior  commis- 
sure, in  front  of  the  central  canal,  consisting  of  medullated  nerve 
fibres,  and  a  posterior  commissure  behind  the  central  canal  consist- 
ing also  of  medullated  nerve-fibres,  but  with  more  neuroglia,  which 
gives  the  grey  aspect  to  this  commissure  (fig.  3 1 6,  b).  Each  half  of  the 


Fig.  316. —  "Different  vieu-s  of  a  portion  of  the  spinal  cord  from  the 
cervical  region,  with  the  roots  of  the  nerves  (slightly  enlarged  . 
In  a,  the  anterior  surface  of  the  specimen  is  shown ;  the 
anterior  nerve-root  of  its  right  side  being  divided;  in  b,  a 
view  of  the  right  side  is  given  ;  in  c,  the  upper  surface  is 
shown ;  in  d,  the  nerve-roots  and  ganglion  are  shown  from 
below.  1.  The  anterior  median  fissure  ;  2,  posterior  median 
fissure  ;  3,  anterior  lateral  depression,  over  which  the  ante- 
rior nerve-roots  are  seen  to  spread ;  4,  posterior  lateral 
groove,  into  which  the  posterior  roots  are  seen  to  sink  ; 
5,  anterior  roots  passing  the  ganglion  ;  5',  in  a,  the  anterior 
root  divided  ;  6,  the  posterior  roots,  the  fibres  of  which  pass 
into  the  ganglion  6';  7,  the  united  or  compound  nerve  ;  7',  the 
posterior  primary  branch,  seen  in  a  and  d  to  be  derived  in 
part  from  the  anterior  and  in  part  from  the  posterior  root. 
(Allen  Thomson). 


CHAP.   XVIII.  ] 


STRUCTtJEB   OF   SPINAL  CORD. 


567 


spinal  cord  is  marked  on  the  sides  (obscurely  a1  the  lower  part,  but 
distinctly  above)  by  two  longitudinal  furrows,  which  divide  it  into 
three  portions,  columns,  or  tracts,  an  anterior,  lateral,  and  pos- 
terior. From  the  groove  between  the  anterior  and  Lateral  columns 
spring  the  anterior  roots  of  the  spinal  nerves  (b  and  C,  5)  ;  :iiid 
just  in  front  of  the  groove  between  the  lateral  and  posterior 
column  arise  the  posterior  roots  of  the  same  (n,  6) :  a  pair  of  roots 
on  each  side  corresponding  to  each  vertebra  (fig.  317). 

White  matter. — The  white  matter  of  the  cord  is  made  up  of 
medullated  nerve  fibres,  of  various  sizes,  arranged  longitudinally 
around  the  cord  under  the  pia  mater  and  passing  in  to  support 
the  individual  fibres  in  the  delicate  connective  tissue  or  neuroglia 
made  up  of  a  very  fine  reticulum,  with  both  small  cells  almost 
filled  up  by  nuclei  and  stellate,  branching  corpuscles. 


Fig.  317. — Section  of  grey  matter  of  anterior  cornu  ef  a  calf's  spinal  cord;  nf,  nerve-fibres 
of  white  matter  in  transverse  section,  showing  axis-cylinder  in  centre  of  each ;  a  rf 
anterior  roots  of  spinal  nerve  passing  out  through  white  matter ;  g  c,  large  stellate 
nerve-cells  with  nuclei ;  they  are  seen  imbedded  in  neuroglia.     (Schofield.) 

Size. — The  general  rule  respecting  the  size  of  different  parts  of 
the  cord  appears  to  be,  that  the  size  of  each  part  bears  a  direct  pro- 
portion to  the  size  and  number  of  nerve-roots  given  off  from  itself, 
and  has  but  little  relation  to  the  size  or  number  of  those  given  off 
below  it.  Thus  the  cord  is  very  large  in  the  middle  and  lower 
part  of  its  cervical  portion,  whence  arise  the  large  nerve-roots  for 


568  THE  NEBVOUS   SYSTEM.  [chap,  xyiii. 

the  formation  of  the  brachial  plexuses  and  the  supply  of  the  upper 
extremities,  and  again  enlarges  at  the  lowest  part  of  its  dorsal  por- 
tion and  the  upper  part  of  its  lumbar,  at  the  origins  of  the  large 
nerves  which,  after  forming  the  lumbar  and  sacral  plexuses,  are  dis- 
tributed to  the  lower  extremities.  The  chief  cause  of  the  greater 
size  at  these  parts  of  the  spinal  cord  is  increase  in  the  quantity  of 
grey  matter  ;  for  there  seems  reason  to  believe  that  the  white  or 
fibrous  part  of  the  cord  becomes  gradually  and  progressively  larger 
from  below  upwards,  doubtless  from  the  addition  of  a  certain 
number  of  upward  passing  fibres  from  each  pair  of  nerves. 

From  careful  estimates  of  the  number  of  nerve-fibres  in  a  trans- 
verse section  of  the  cord  towards  its  upper  end,  and  the  number 
entering  it  by  the  anterior  and  posterior  roots  of  each  pair  of 
nerves,  it  has  been  shown  that  in  the  human  spinal  cord  not  more 
than  half  of  the  total  number  of  nerve-fibres  entering  the  cord 
through  all  the  spinal  nerves  are  contained  in  a  transverse  section 
near  its  upper  end.  It  is  obvious,  therefore,  that  at  least  half  of 
the  nerve-fibres  entering  it  must  terminate  in  the  cord  itself. 

Grey  matter. — The  grey  matter  of  the  cord  consists  essentially 
of  an  extremely  delicate  network  of  the  primitive  fibrillee  of 
axis-cylinders,  and  which  are  derived  from  the  ramification  of 
multipolar  ganglion  cells  of  very  large  size,  containing  large  round 
nuclei  with  nucleoli.  This  fine  plexus  is  called  Gerlach's  network, 
and  is  mingled  with  the  meshes  of  neuroglia,  which  in  some  parts 
is  chiefly  fibrillated,  in  others  mainly  granular  and  punctiform. 
The  neuroglia  is  prolonged  from  the  surface  into  the  tip  of  the . 
posterior  cornu  of  grey  matter  and  forms  a  jelly-like  transparent 
substance,  which  when  hardened  is  found  to  be  reticular,  and  is 
called  the  substantia  gelatinosa  of  Rolando. 

The  multipolar  cells  are  either  scattered  singly  or  arranged  in 
groups,  of  which  the  following  are  to  be  distinguished: — (a)  In 
the  anterior  cornu.  The  groups  found  in  the  anterior  cornu  are 
generally  two — one  at  the  lateral  part  near  the  lateral  column, 
and  the  other  at  the  tip  of  the  cornu  in  the  middle  line — some- 
times, as  in  the  lumbar  enlargement,  there  is  a  third  group  more 
posterior.  The  cells  of  the  anterior  group  are  the  largest.  Into 
many  of  these  cells  the  fibres  of  the  anterior  motor  nerve-roots  can 
be  distinctly  traced,  (b.)  In  the  tractus  intermedio-lateralis.  A 
group  of  nerve-cells  midway  between  the   anterior   and  posterior 


(MAT.    XVIII.] 


SPINAL   NERVES. 


$0j 


cornua,  near  the  external  surface  of  the  grey  matter.  It  is 
especially  developed  in  the  dorsal  and  also  in  the  upper  cervical 
region,  (c.)  In  the  posterior  vesicular  columns  of  Lockhart  Clarke. 
These  are  found  in  the  posterior  cornua  of  grey  matter  towards 
tin'  inner  surface,  extending  from  the  cervical  enlargement  to  the 
third  lumbar  nerves  (fig. 
318,  c).  | '/.)  Smaller  cells 
are  scattered  throughout 
the  grey  matter,  but  are 
found  chiefly  at  the  tip 
(caput  cornu)  of  the  poste- 
rior cornu,  in  a  finely  gran- 
ular basis,  and  among  the 
posterior  root  fibres  {sub- 
stantia gelatinosa  cinerea  of 
Rolando). 

The  nerve-cells  are  con- 
nected by  their  processes 
immediately  with  the  axis- 
cylinders  of  the  fibres  of 
the  anterior  or  motor  nerve- 
roots  :  whereas  the  nerve- 
cells  of  the  posterior  roots 
are  connected  with  nerve- 
fibres,  not  directly,  but  only 
through  the  intermediation 
of  Gerlach's  nerve-network, 
in  which  their  branching 
processes  lose  themselves. 

Spinal  Nerves.  —  The 
spinal  nerves  consist  of 
thirty -one     pairs,     issuing 


Fig1.  .318. —  Transverse  section  of  half  the  spinal  ror<f 
in  the  lumbar  enlargement  (semi-diagrammatic  . 
1 .  Anterior  median  fissure ;  2,  posterior  median 
fissure  ;  3,  central  canal  lined  with  epithelium  ; 
\,  posterior  commissure ;  5,  anterior  commis- 
sure ;    6,  posterior  column  ;  7,  lateral  column  ; 

8,  anterior  column.  The  white  substance  is 
traversed  by  radiating  trabecule  of  pia  mater. 

9,  Fasiculus  of  posterior  nerve-root  entering'  in 
one  bundle ;  10,  fasciculi  of  anterior  roots  en- 
tering in  four  spreading  bundles  of  fibres  ;  b,  in 
the  cervix  cornu,  decussating  fibres  from  the 
nerve-roots  and  posterior' commissure ;  <\  pos- 
terior vesicular  columns  of  Lockhart  Clark'-. 
About  half  way  between  the  central  canal  and 
7  are  seen  the  group  of  nerve-cells  forming  the 
tractus  intermedio-lateralis  ;  ►,  e,  fibres  of  an- 
terior roots ;  <■',  fibres  of  anterior  roots  which 
decussate  in  anterior  commissure.  (Allen 
Thomson.)     x  6. 


from  the  sides  of  the  whole 
length  of  the  cord,  their  number  corresponding  with  the  inter- 
vertebral foramina  through  which  they  pass.  Each  nerve  arise- 
by  two  roots,  an  anterior  and  posterior,  the  latter  being  the  largen 
The  roots  emerge  through  separate  apertures  of  the  sheath  of  dura 
mater  surrounding  the  cord  :  and  directly  after  their  emergence, 
where  the  roots  lie  in  the  intervertebral  foramen,  a  ganglion  is  found 


570  THE  NERVOUS   SYSTEM.  [chap.  xvnr. 

on  the  posterior  root.  The  anterior  root  lies  in  contact  with  the 
anterior  surface  of  the  ganglion,  but  none  of  its  fibres  intermingle 
with  those  in  the  ganglion  (5,  fig.  316).  But  immediately  beyond 
the  ganglion  the  two  roots  coalesce,  and  by  the  mingling  of  their 
fibres  form  a  compound  or  mixed  spinal  nerve,  which,  after  issuing 
from  the  intervertebral  canal,  divides  into  an  anterior  and  pos- 
terior branch,  each  containing  fibres  from  both  the  roots  (fig.  316). 

The  anterior  root  of  each  spinal  nerve  arises  by  numerous 
separate  and  converging  bundles  from  the  anterior  column  of  the 
cord ;  the  posterior  root  by  more  numerous  parallel  bundles, 
from  the  posterior  column,  or,  rather,  from  the  posterior  part  of 
the  lateral  column  (fig.  318),  for  if  a  fissure  be  directed  inwards 
from  the  groove  between  the  middle  and  posterior  columns,  the 
posterior  roots  will  remain  attached  to  the  former.  The  anterior 
roots  of  each  spinal  nerve  consist  of  centrifugal  fibres  ;  the  pos- 
terior as  exclusively  of  centripetal  fibres. 

Course  of  the  Fibres  of  the  Spinal  Nerves. — (a)  The  An- 
terior  roots  enter  the  cord  in  several  bundles  which  may  be  called  : — 
(1)  Internal;  (2)  Middle;  (3)  External;  all  being  more  or  less 
connected  with  the  groups  of  multipolar  cells  in  the  anterior 
cornua.  1.  The  internal  fibres  are  partly  connected  with  internal 
group  of  nerve  cells  of  anterior  cornu  of  the  same  side  ;  but  some 
fibres  pass  over,  through  anterior  commissure  to  end  in  the 
anterior  comu  of  opposite  side,  probably  in  internal  group  of  cells. 
2.  The  middle  fibres  are  partly  in  connection  with  the  lateral  group 
of  cells  in  anterior  cornu,  and  in  part,  pass  backwards  to  posterior 
cornu,  having  no  connection  with  cells.  3.  The  external  fibres 
are  partly  in  connection  with  the  lateral  group  of  cells  in  the 
anterior  comu,  but  some  fibres  proceed  direct  into  the  lateral 
column  without  connection  with  cells  and  pass  upwards  in  it. 

(//)  The  Posterior  roots  enter  the  posterior  cornua  in  two  chief 
bundles,  either  at  the  tip,  through  or  round  the  substantia  gela- 
tinosa,  or  by  the  inner  side.  The  former  enter  the  grey  matter  at 
once,  and  as  a  rule,  turn  upwards  or  downwards  for  a  certain  dis- 
tance and  then  pass  horizontally,  some  fibres  reach  the  anterior 
cornua,  passing  at  once  horizontally ;  and  the  others,  the  opposite 
side,  through  the  posterior  grey  commissure.  Of  those  which 
enter  by  the  inner  side  of  the  cornua  the  majority  pass  up  (or 
flown)  in  the  white  substance  of  the  posterior  columns,  and  enter 


chap,  xvih.]        STRUCTURE   OF   BPINAL   NERVES. 


571 


the  grey  matter  at  various  heights  al  the  base  of  the  posterior 
eornu,  perhaps  Borne  pass  directly  upwards  without  entering  the 
•jiv\  matter.  Those  that  enter  the  grey  matter  pass  in  various 
directions,  some  to  join  the  lateral  cells  in  the  anterior  cornu, 
.some  join  the  cells  in  the  posterior  vesicular  column,  and  Borne 
across  to  the  other  side  of  the  cord  in  the  anterior  commis- 
sure,  whilst  others  become  again  longitudinal  in  the  grey  matter. 

It    should  be  here    mentioned  that  the  cells  in   the  posterior 
vesicular  column  are  connected  with  medullated  fibres  which  pass 
horizontally  to  the  white 
matter     of    the     lateral 
columns       and        there 
become  longitudinal. 

Course  of  tJu  fibres  in 
the  cord.  The  nerve  fibres 
which  form  the  white 
matter  of  the  curd  are 
nearly  all  longitudinal 
fibres.  It  is,  however, 
a  matter  of  great  diffi- 
culty t"  trace  these 
fibres  by  mere  die 
tion,  and  so  some  other 

methods  must  be  adopted.  One  method  is  based  upon  the  fact 
that  nerve  fibres  undergo  degeneration  when  they  are  cut  off 
from  the  centre  with  which  they  are  connected,  or  when  the  parts 
to  which  they  are  distributed  are  removed,  as  in  amputation 
of  a  limb  ;  and  information  as  to  the  course  of  the  fibres  has 
been  obtained  by  tracing  the  course  of  these  degenerated  tracts. 
The  second  method  consists  in  observing  the  development  of 
the  various  tracts;  some  have  their  medullary  substance  later  than 
others,  and  are  to  be  distinguished  by  their  more  grey  appearance. 
The  chief  tracts  which  have  been  made  out  are  the  following: — 
(1)  The  direct  pyramidal  trad  (fig.  319  d.p.t.),  a  comparatively 
small  portion  of  the  inner  part  of  the  anterior  columns,  which  is 
traceable  from  the  anterior  pyramids  of  the  medulla  to  the  mid- 
dorsal  region  of  the  spinal  cord.  It  consists  of  the  fibres  of  the 
pyramids  which  do  not  undergo  decussation  in  the  medulla. 
There  is  reason  for  believing,  however,  that    these   fibres   of  the 


P.M.C 


Fig.  ',19. — Diagram  of  the  spinal  cord  at  the  lowei 

cni  region  to  show  the  track  of  fibres;  </.  //.  t., 
direct  pyramidal  tract;  c.  }>.  /.,  crossed  pyrami- 
dal tract ;  *  direct  cerebellar  tract ;  p.  m.  c,  pos- 
terior medium  column.    (Gowers.) 


572  THE  NERYOUS   SYSTEM.  [chap.  xvnr. 

direct  pyramidal  tract  undergo  decussation  throughout  their  course, 
and  fibres  pass  over  through  the  anterior  commissure  to  join 
the  lateral  pyramidal  tract  (vide  infra) ;  (2)  the  Grossed  pyramidal 
tract  (fig.  319,  c.p.t.)  can  be  traced  from  the  anterior  pyramids  of  the 
medulla,  and  consists  of  fibres  which  decussate  in  the  anterior  fissure 
and  pass  downwards  in  the  lateral  columns  near  the  posterior  cornu 
of  the  grey  matter  to  the  lower  end  of  the  cord;  (3)  Direct  cere- 
bellar tract  (fig.  319),  which  corresponds  to  the  peripheral  portion  of 
the  posterior  lateral  column  between  the  crossed  pyramidal  tract 
and  the  edge  of  the  cord,  can  be  traced  up  directly  to  the  cerebellum 
and  down  to  the  mid-lumbar  region ;  (4)  Posterior  medium  column. 
or  Fasciculus  of  GolL  is  found  on  either  side  of  the  posterior  commis- 
sure, and  is  traceable  upwards  as  the  fasciculus  gracilis  of  the 
medulla,  the  fibres  are  connected  with  the  cells  of  the  posterior 
vesicular  column.  It  is  traceable  downwards  to  the  mid-dorsal 
region.  As  regards  the  remaining  part  of  the  cord  unoccupied  by 
the  above  tracts  little  can  be  said.  The  portion  of  the  posterior 
column  between  the  posterior  median  column  and  the  posterior 
roots  of  the  spinal  nerves,  known  as  fasciculus  cuneatus  or  Bur- 
dach's  column,  is  composed  of  fibres  of  the  posterior  roots  on  their 
way  to  enter  the  grey  substance  at  different  heights.  The  antero- 
lateral column  contains  fibres  from  the  anterior  cornua  of  the 
same  as  well  as  of  the  opposite  side. 

Functions  of  the  Spinal  Nerves. — The  anterior  spinal  nerve- 
roots  are  efferent  or  motor  :  the  posterior  are  afferent  or  sensory 
(Sir  C.  Bell).  The  fact  is  proved  in  various  ways.  Division  of 
the  anterior  roots  of  one  or  more  nerves  is  followed  by  complete 
loss  of  motion  in  the  parts  supplied  by  the  fibres  of  such  roots  : 
but  the  sensation  of  the  same  parts  remains  perfect.  Division  of 
the  posterior  roots  destroys  the  sensibility  of  the  parts  supplied  by 
their  fibres,  while  the  power  of  motion  continues  unimpaired. 
Moreover,  irritation  of  the  ends  of  the  distal  portions  of  the 
divided  anterior  roots  of  a  nerve  excites  muscular  movements  : 
irritation  of  the  ends  of  the  proximal  portions,  which  are  still  in 
connection  of  the  cord,  is  followed  by  no  appreciable  effect.  Irri- 
tation of  the  distal  portions  of  the  divided  posterior  roots,  on  the 
other  hand,  produces  no  muscular  movements  and  no  manifesta- 
tions of  pain  ;  for,  as  already  stated,  sensory  nerves  convey  impres- 


cHAr.  xviii.]  FTJNCTI0N8  01    SPINAL  COED.  573 

nly  towards   the  nervous   centres  :    but  irritation   of  the 
proximal  portions  of  these  roots  elicil  of  intense  Buffering. 

Occasionally,  under  this  last   irritation,  muscular  movei  lso 

ensue;  but  these  are  either  voluntary,  or  the  result  of  the  irrita- 
tion being  reflected  from  the  Bensory  to  the  motor  fibres.     Oo 
sionally,  too,   irritation   of  the   distal    ends   of  divided   anterior 
roots  elicits  signs  of  pain,  as  well  as  producing  muscular  moi 
ments:  the   pain   thus   excited  is  probably  the   result  either  of 

np  or  of  so-called  recurrent  sensibility  (  Brown-Sequard). 
Recurrent  Sensibility. — If  the  anterior  root  of  a  spinal  m 
be  divided  and  the  peripheral  end  be  irritated,  not  only  move- 
ments of  the  muscles  supplied  by  the  nerve  take  place,  but  also  of 
other  muscles,  indicative  of  pain.     If  the  main  trunk  of  the  nerve 
(after  the  coalescence  of  the  roots  beyond  the  ganglion)  be  divid< 
and  the  anterior  root  be  irritated  as  before,  the  general  signs  of 
pain  still  remain,  although  the  contraction  of  the  muscli  !iot 

ur.  The  signs  of  pain  disappear  when  the  posterior  root  is 
divided.  From  these  experiments  it  is  believed  that  the  stimulus 
passes  down  the  anterior  root  to  the  mixed  nerve  and  returns  to  the 
central  nervous  system  through  the  posterior  root  by  means  of 
certain  sensory  fibres  from  the  posterior  root,  which  loop  back 
into  the  anterior  root,  before  continuing  their  course  into  the 
mixed  nerve-trunk. 

Functions  of  the  Ganglia  on  Posterior  Roots. — The 
ganglia  act  as  centres  for  the  nutrition  of  the  nerves,  since  when 
the  nerves  are  severed  from  connection  with  the  ganglia,  the  pails 
of  the  nerves  so  severed  degenerate,  whilst  the  parts  which  remain 
in  connection  with  them  do  not. 

Functions  of  the  Spinal  Cord. 
The  power  of  the  spinal  cord,  as  a  nerve-centre,  may  l>e  arranged 
under  the  heads  of  (1)  Conduction  ;  (2)  Transference  :    (5;  Keflex 
action. 

(1)   Conduction. — The  functions  of  the  spinal  cord  in  relation  to 

nducticm,  maybe  best  remembered  by  considering  its  anatomical 

onections  with  other  parts  of  the  body.     From  th<  se  it  isevident 

that,  with  the  exception  of  some  few  filaments  of  th..-  sympath* 

there  is  noway  by  which  nerve-impulses  can  be  conveyed  from  the 

trunk  ami  extremities  to  the  brain  or  -  ther  than  that 


574  TIIE  NERVOUS   SYSTEM.  [chap.  xvnr. 

formed  by  the  spinal  cord.  Through  it,  the  impressions  made 
upon  the  peripheral  extremities  or  other  parts  of  the  spinal  sensory 
nerves  are  conducted  to  the  brain,  where  alone  they  can  be  per- 
ceived. Through  it,  also,  the  stimulus  of  the  will,  conducted  from 
the  brain,  is  capable  of  exciting  the  action  of  the  muscles  supplied 
from  it  with  motor  nerves.  And  for  all  these  conductions  of  im- 
pressions to  and  fro  between  the  brain  and  the  spinal  nerves, 
the  perfect  state  of  the  cord  is  necessary ;  for  when  any  part  of  it 
is  destroyed,  and  its  communication  with  the  brain  is  interrupted, 
impressions  on  the  sensory  nerves  given  off  from  it  below  the  seat 
of  injury,  cease  to  be  propagated  to  the  brain,  and  the  brain  loses. 
the  power  of  voluntarily  exciting  the  motor  nerves  proceeding  from 
the  portion  of  cord  isolated  from  it.  Illustrations  of  this  are 
furnished  by  various  examples  of  paralysis,  but  by  none  better 
than  by  the  common  paraplegia,  or  loss  of  sensation  and  voluntary 
motion  in  the  lower  part  of  the  body,  in  consequence  of  destruc- 
tive disease  or  injury  of  a  portion,  including  the  whole  thickness, 
of  the  spinal  cord.  Such  lesions  destroy  the  communication 
between  the  brain  and  all  parts  of  the  spinal  cord  below  the  seat 
of  injury,  and  consequently  cut  off  from  their  connection  with  the 
brain  the  various  organs  supplied  with  nerves  issuing  from  those 
parts  of  the  cord. 

It  is  probable  that  the  conduction  of  impressions  along  the  cord 
is  effected  (at  least,  for  the  most  part)  through  the  grey  sub- 
stance, i.e.,  through  the  nerve-corpuscles  and  filaments  connecting 
them.  But  all  parts  of  the  cord  are  not  alike  able  to  conduct  all 
impressions  ;  and  as  there  are  separate  nerve-fibres  for  motor  and 
for  sensory  impressions,  so  in  the  cord,  separate  and  determinate 
parts  serve  to  conduct  always  the  same  kind  of  impression. 

Experiments  (chiefly  by  Brown-Sequard),  point  to  the  following- 
conclusions  regarding  the  conduction  of  sensory  and  motor  impres- 
sions through  the  spinal  cord. 

It  is  important  to  bear  in  mind  that  the  grey  matter  of  the  cord, 
though  it  conducts  impressions  giving  rise  to  sensation,  appears 
not  to  be  sensitive  when  it  is  directly  stimulated.  The  explana- 
tion probably  is,  that  it  possesses  no  apparatus  such  as  exists  at 
the  peripheral  terminations  of  sensory  nerves,  for  the  reception  of 
sensory  impressions. 

a.    Sensory  impressions,  conveyed  to  the  spinal  cord  by  root- 


OH  IP,  Will.  ] 


li  ACTIONS  OF  SPINAL  CORD. 


575 


fibres  of  the  posterior  nerves  are  nol  oonducted  to  the  brain  only 
by  the  posterior  columns  of  the  cord,  but  pass  through  them  in 
great  pari  into  the  central  grey  Bubstance,  by  which  they  are 
transmitted  to  the  brain  (p  r,  fig.  320). 

b.  The  impressions  thus  conveyed  to  the  grey  substance  do  not 
pass  up  to  the  brain  to  more  than  a  Blight  degree,  along  that  half 
of  the  cord  corresponding  to  the  side  from  which  they  have  been 
received,  bul  cross  over  to  the  other  side  almost  immediately  after 


Fig.  320. — Diagram  of  the  decussation  of  the  conductors  for  voluntary  movements,  and  those  for 
sensation  :  «,  r,  anterior  roots  and  their  continuations  in  the  spinal  cord,  and  decussa- 
tion at  the  lower  part  of  the  medulla  oblongata,  m  o  ;  p  r,  the  posterior  roots  and 
their  continuation  and  decussation  in  the  spinal  cord  ;  g  g,  the  ganglions  of  the  roots. 
The  arrows  indicate  the  direction  of  the  nervous  action ;  r,  the  right  side  ;  I,  the  left 
side.  1,  2,  3,  indicate  places  of  alteration  in  a  lateral  half  of  the  spino-cerebral  axis,  to 
show  the  influence  on  the  two  kinds  of  conductors,  resulting  from  section  of  the  cord 
at  any  one  of  these  three  places.     (After  Brown-Sequard.) 

entering  the  cord,  and  along  it  are  transmitted  to  the  brain. 
There  is  thus,  in  the  cord  itself,  an  almost  complete  decussation 
of  sensory  impressions  brought  to  it ;  so  that  division  or  disease  of 
one  posterior  half  of  the  cord  (3,  fig.  320)  is  followed  by  loss  of 
sensation,  not  in  parts  on  the  corresponding,  but  in  those  of  the 
opposite  side  of  the  body.      From  the  same  fact  it  happens  that  a 


576  THE  XERVOUS   SYSTEM.  [chap.  xvnr. 

longitudinal  anteroposterior  section  of  the  cord,  along  its  whole 
length  most  completely  abolishes  Bensibility  on  both  sides  of  the 
body. 

e.  The  various  sensations  of  touch,  pain,  temperature,  and 
muscular  contraction,  are  probably  conducted  along  separate  and 
distinct  sets  of  fibres.  All,  however,  with  the  exception  of  the  last 
named,  undergo  decussation  in  the  spinal  cord. 

d.  The  posterior  columns  of  the  cord  appear  to  have  a  great 
share  in  reflex  movements. 

e.  Impulses  of  the  will,  leading  to  voluntary  contractions  of 
muscles,  appear  to  be  transmitted  principally  along  the  antero- 
lateral columns  ;  but  if  a  transverse  section  of  this  part  be  made 
(the  grey  matter  being  intact)  although  at  first  no  voluntary  move- 
ments of  the  part  below  occur,  this  paralysis  is  only  temporary 
indicating  that  the  grey  matter  may  take  on  the  conduction  of 
these  impulses. 

/.  Decussation  of  motor  impulses  occurs,  not  in  the  spinal  cord, 
as  is  the  case  with  sensory  impressions,  but  at  the  anterior  part 
•of  the  medulla  oblongata  (fig.  321).  Hence,  motor  impulses, 
having  made  their  decussation,  first  enter  the  cord  by  the  lateral 
tracts  and  adjoining  grey  matter,  and  then  pass  to  the  anterior 
columns  and  to  the  grey  matter  associated  with  them.  Accord- 
ingly, division  of  the  anterior  pyramids,  at  the  point  of  decussation 
(2,  fig.  320),  is  followed  by  paralysis  of  motion  in  all  parts  below ; 
while  division  of  the  olivary  bodies  which  constitute  the  true 
continuations  of  the  anterior  columns  of  the  cord,  appears  to 
produce  very  little  paralysis.  Disease  or  division  of  any  part 
of  the  cerebro-spinal  axis  above  the  seat  of  decussation  (1,  fig.  320) 
Is  followed,  as  well-known,  by  impaired  or  lost  power  of  motion 
on  the  opposite  side  of  the  body ;  while  a  like  injury  inflicted 
below  this  part  (3,  fig.  320),  induces  similar  paralysis  on  the 
corresponding  side. 

"When  one  half  of  the  spinal  cord  is  cut  through,  complete 
anaesthesia  of  the  other  Bide  of  the  body  below  the  point  of  section 
results,  but  there  is  often  greatly  increased  sensibility  (hyper- 
esthesia) on  the  same  side  :  so  much  so  that  the  least  touch 
appears  to  be  agonising.  This  condition  may  persist  for  several 
days.  Similar  effects  may,  in  man.  be  the  result  of  injury.  Thus, 
in  a  patient  who  had  sustained  a  severe  lesion  of  the  spinal  cord 


chat,  win.  1  FUNCTIONS  OF   .-PINAL  CORD.  577 

in  the   <-rrvi«Ml    region,  causing   extensive   paralysis  and  lot 
sensation  in  tin-  lower  balf  of  the  body,  there  were  two  circum 
scribed  areas,  one  on  each  arm,  symmetrically  placed,  in  which  the 
gentlest  touch  caused  extreme  pain. 

In  addition  to  the  transmission  of  ordinary  sensory  and  motor 
impulses,  the  spinal  cord  is  the  medium  of  conduction  also  oi  im- 
pulses to  and  from  the  vcuo-ntotor  centre  in  the  medulla  oblong 
and  probably  also  contains  special  vase-motor  centres. 

2.  Transference. — Examples  of  the  transference  of  impressions 
in  the  cord  have  been  given  (p.  55S) ;  and  that  the  transference 
takes  place  in  the  cord,  and  not  in  the  brain,  is  nearly  proved  by 
the  frequent  eases  of  pain  felt  in  the  knee  and  not  m  the  hip,  in 

of  the  hip;  of  pain  felt  in  the  urethra  or  glans  penis, 
and  not  in  the  bladder,  in  calculus ;  for,  if  both  the  primary  and 
the  secondary  or  transferred  impression  were  in  the  brain,  loth 
should  be  felt. 

3.  Reflection- — In  man  the  spinal  cord  is  so  much  under  the 
control  of  the  higher  nerve-centres,  that  its  own  individual  func- 
tions in  relation  to  reflex  action  are  apt  to  be  overlooked  :  so  that 
the  result  of  injury,  by  which  the  cord  is  cut  off  completely  from 
the  influence  of  the  encephalon,  is  apt  to  lessen  rather  than  in- 
crease our  estimate  of  its  importance  and  individual  endowments 
Thus,  when  the  human  spinal  cord  is  divided,  the  lower  extremities 
fall  into  any  position  that  their  weight  and  the  resistance  of  sur- 
rounding objects  combine  to  give  them;  if  the  body  is  irritated, 
they  do  not  move  towards  the  irritation ;  and  if  they  are  touched, 
the  consequent  reflex  movements  are  disorderly  and  purposeless ; 
all  power  of  voluntary  movement  is  absolutely  abolished.  In  other 
mammals,  e.g.,  rabbit  or  dog,  after  recovery  from  the  shock  of  the 
operation,  which  takes  some  time,  reflex  actions  in  the  parts  below 
will  occur  after  the  spinal  cord  has  been  divided,  a  very  feeble 
irritation  being  followed  by  extensive  and  co-ordinate  movements. 
Tn  the  case  of  the  frog,  however,  and  many  other  cold-blooded 
animals,  in  which  experimental  and  other  injuries  of  the  nerve 
tissues  are  better  home,  and  in  which  the  lower  nerve-centres  are 

subordinate  in  their  action  to  the  higher,  the  reflex  functions 

of  the  cord  arc  still  more  clearly  shown.     When,  for  example,  a 

r/s  head  is  cut  off,  the  limbs  remain  in,  or  assume  a  natural 

position  ;   they  resume  it  when  disturbed  :   and  when  the  abdomen 

or  back  is  irritated,  the  feet  are  moved  with  the  manifest  purpose 

p  p 


578  THE  NERVOUS   SYSTEM.  [chat,  xviii. 

of  pushing  away  the  irritation.  The  main  difference  in  the  cold- 
blooded animals  being  that  the  reflex  movements  are  more  definite, 
complicated,  and  effective,  although  less  energetic  than  in  the  case 
of  mammals.  It  is  as  if  the  mind  of  the  animal  were  still  engaged 
in  the  acts ;  and  yet  all  analogy  would  lead  us  to  the  belief  that 
the  spinal  cord  of  the  frog  has  no  different  endowment,  in  hind, 
from  those  which  belong  to  the  cord  of  the  higher  vertebrata :  the 
difference  is  only  in  degree.  And  if  this  be  granted,  it  may  be 
assumed  that,  in  man  and  the  higher  animals,  many  actions  are 
performed  as  reflex  movements  occurring  through  and  by  means  of 
the  spinal  cord,  although  the  latter  cannot  by  itself  initiate  or 
even  direct  them  independently. 

Co-ordinate  Movement  not  a  proof  of  Consciousness.— 
The  evident  adaptation  and  purpose  in  the  movements  of  the 
cold-blooded  animals,  have  led  some  to  think  that  they  must  be 
conscious  and  capable  of  will  without  their  brains.  But  purposive 
movements  are  no  proof  of  consciousness  or  will  in  the  creature 
manifesting  them.  The  movements  of  the  limbs  of  headless  frogs 
are  not  more  purposive  than  the  movements  of  our  own  respiratory 
muscles  are  ;  in  which  we  know  that  neither  will  nor  consciousness 
is  at  all  times  concerned.  It  may  not,  indeed,  be  assumed  that  the 
acts  of  standing,  leaping,  and  other  movements,  which  decapitated 
cold-blooded  animals  can  perform,  are  also  always,  in  the  entire  and 
health}'  state,  performed  involuntarily,  and  under  the  sole  influence 
of  the  cord  ;  but  it  is  probable  that  such  acts  may  be,  and  com- 
monly are,  so  performed,  the  higher  nerve-centres  of  the  animal 
having  only  the  same  kind  of  influence  in  modifying  and  directing 
them,  that  those  of  man  have  in  modifying  and  directing  the 
the  movements  of  the  respiratory  muscles. 

Inhibition  of  Reflex  Actions. — The  fact  that  such  move- 
ments as  are  produced  by  iritating  the  skin  of  the  lower  ex- 
tremities in  the  human  subject,  after  division  or  disorganisation  of 
a  part  of  the  spinal  cord,  do  not  follow  the  same  irritation  when 
the  mind  is  active  and  connected  with  the  cord  through  the  brain, 
is,  probably,  due  to  the  mind  ordinarily  perceiving  the  irritation 
and  instantl}'  controlling  the  muscles  of  the  irritated  and  other 
parts  ;  for,  even  when  the  cord  is  perfect,  such  involuntary  move- 
ments will  often  follow  irritation,  if  it  be  applied  when  the  mind 
is  wholly  occupied.  "When,  for  example,  one  is  anxiously  thinking, 
even  slight   stimuli  will   produce  involuntary  and  reflex   move- 


chap,  win  ]  FUNCTIONS  OF  SPINAL  COED.  579 

ments.  So,  also,  during  Bleep,  such  reflex  movements  maj  !><• 
observed,  when  the  skin  is  touched  or  tickled  ;  for  example,  when 
one  touches  with  the  finger  the  palm  of  the  band  of  a  Bleeping 
child,  the  finger  is  grasped — the  impression  on  the  skin  of  the 
palm  producing  a  reflex  movemenl  of  the  muscles  which  close  the 
hand.  But  when  the  child  is  awake,  n<>  such  effect  is  produced  by 
a  similar  touch. 

Further,  many  reflex  actions  are  capable  of  being  more  or  less 
controlled  or  even  altogether  prevented  by  the  will  :  thus  an 
inhibitor//  action  may  be  exercised  by  the  brain  over  reflex  func- 
tions of  the  cord  and  the  other  nerve  centres.  The  following  may 
be  quoted  as  familiar  examples  of  this  inhibitory  action  : — 

To  prevent  the  reflex  action  of  crying  out  when  in  pain,  it  is 
iften  sufficient  firmly  to  clench  the  teeth  or  to  grasp  some  object 
and  hold  it  tight.  When  the  feet  arc  tickled  we  can,  by  an 
effort  of  will,  prevent  the  reflex  action  of  jerking  them  up.  So, 
too,  the  involuntary  closing  of  the  eyes  and  starting,  when  a  blow 
is  aimed  at  the  head,  can  be  similarly  restrained. 

Darwin  has  mentioned  an  interesting  example  of  the  way  in 
which,  «>n  the  other  hand,  such  an  instinctive  reflex  aet  may  over- 
ride the  strongest  effort  of  the  will.  He  placed  his  face  close 
gainst  the  glass  of  the  cobra's  cage  in  the  Keptile  House  at  the 
Zoological  Gardens,  and  though,  of  course,  thoroughly  convinced 
of  his  perfect  security,  could  not  by  any  effort  of  the  will  prevent  him- 
self from  starting  back  when  the  snake  struck  with  fury  at  the  glass. 

It  has  been  found  by  experiment  that  in  a  frog  the  optic  lobes 
and  optic  thalami  have  a  distinct  action  in  inhibiting  or  delaying 
reflex  action,  and  also  that  more  generally  any  afferent  stimulus,  if 
sufficiently  strong,  may  inhibit  or  modify  any  reflex  action  even  in 
the  absence  of  these  centres. 

On  the  whole,  therefore,  it  may,  from  these  and  like  facts,  be 
concluded  that  reflex  acts,  performed  under  the  influence  of  the 
reflecting  power  of  the  spinal  cord,  are  essentially  independent  of 
the  brain  and  may  be  performed  perfectly  when  the  brain  is 
separated  from  the  cord:  that  these  include  a  much  larger  number 
of  the  natural  and  purposive  movements  of  the  lower  animals  than 
of  the  warm-blooded  animals  and  man  :  and  that  over  nearly  all  of 
them  the  mind  may  exercise,  through  the  higher  nerve  centres, 
><>me  control;  determining,  directing,  hindering,  or  modifying,  them, 
either  by  direct  action,  or  by  its  power  over  associated  muscles. 

p  r  2 


580  THE   NERVOUS   SYSTEM.  [chat,  xviii. 

To  these  instances  of  spinal  reflex  action,  some  add  yet  many 
more,  including  nearly  all  the  acts  which  seem  to  be  performed 
unconsciously,  such  as  those  of  walking,  running,  writing,  and  the 
like  :  for  these  arc  really  involuntary  acts.  It  is  true  that  at 
their  first  performances  they  are  voluntary,  that  they  require 
education  for  their  perfection,  and  are  at  all  times  so  constantly 
performed  in  obedience  to  a  mandate  of  the  will,  that  it  is  difficult 
to  believe  in  their  essentially  involuntary  nature.  But  the  will 
really  has  only  a  controlling  power  over  their  performance ;  it 
can  hasten  or  stay  them,  but  it  has  little  or  nothing  to  do  with  the 
actual  carrying  out  of  the  effect.  And  this  is  proved  by  the 
circumstance  that  these  acts  can  be  performed  with  complete 
mental  abstraction  :  and,  more  than  this,  that  the  endeavour  to 
carry  them  out  entirely  by  the  exercise  of  the  will  is  not  011I3-  not 
beneficial,  but  positively  interferes  with  their  harmonious  and 
perfect  performance.  Anyone  may  convince  himself  of  this  fact 
by  trying  to  take  each  step  as  a  voluntary  act  in  walking  down 
stairs,  or  to  form  each  letter  or  word  in  writing  by  a  distinct 
exercise  of  the  will. 

These  actions,  however,  will  be  again  referred  to,  when  treating 
of  their  possible  connection  with  the  functions  of  the  so-called 
sensory  ganglia,  p.  593  et  seq. 

Morbid  reflex  actions. — The  relation  of  the  reflex  action  to  the 
strength  of  the  stimulus  is  the  same  as  was  shewn  generally  in  the 
action  of  ganglia,  a  slight  stimulus  producing  a  slight  (p.  562) 
movement  and  a  greater,  a  greater  movement,  and  so  on ;  but 
in  instances,  in  which  we  must  assume  that  the  cord  is  morbidly 
more  irritable,  i.e.,  apt  to  issue  more  nervous  force  than  is  propor- 
tionate to  the  stimulus  applied  to  it,  a  slight  impression  on  a  sen- 
sory nerve  produces  extensive  reflex  movements.  This  appears  to  be 
the  condition  in  tetanus,  in  which  a  slight  touch  on  the  skin 
may  throw  the  whole  body  into  convulsion.  A  similar  state  is 
induced  by  the  introduction  of  strychnia,  and,  in  frogs,  of  opium, 
into  the  blood ;  and  numerous  experiments  on  frogs  thus  made 
tetanic,  have  shown  that  the  tetanus  is  wholly  unconnected  with 
the  brain,  and  depends  on  the  state  induced  in  the  spinal  cord. 

Special  Centres  in  Spinal  Cord. — It  may  seem  to  have  been 
implied  that  the  spinal  cord,  as  a  single  nerve-centre,  reflects  alike 
from  all  parts  all  the  impressions  conducted  to  it.  But  it  is  more 
probable  that  it  should  be  regarded  as  a  collection  of  nervous 


bap.  win..    SPECIAL  CENTRES    IN   SPINAL  CORD.  cgj 

centres  united  in  a  continuous  column.  Tins  is  made  probable  by 
the  fact  that  segments  of  the  cord  may  acl  as  distincl  nerve 
contres,  and  excite  motions  in  the  parts  supplied  with  nerves  given 

off  from  them  ;    as  well  as  lev  the  analogy  of  certain  cases  in  which 

the  muscular  movements  of  single  organs  are  under  the  control  of 
certain  circumscribed  portions  of  the  cord.  Thus, — for  the  govern- 
ance of  the  sphincter-muscles  concerned  in  guarding  the  orifices 
respectively  of  the  rectum  and  urinary  bladder  there  are  special 
nerve-centres  in  the  lower  part  of  the  spinal  cord  {ano-spinal  and 
vesicospinal  centres)  ;  while  the  actions  of  these  are  temporarily 
inhibited  by  stimuli  which  lead  to  defalcation  and  micturition. 
So  also,  there  are  centres  directly  concerned  in  erection  of  the 
penis  and  in  the  emission  of  semen  (genitourinary).  The  emission 
of  semen  is  a  reflex  act  :  the  irritation  of  the  glans  penis  conducted 
to  the  spinal  cord,  and  thence  reflected,  excites  the  successive  and 
co-ordinate  contractions  of  the  muscular  fibres  of  the  vasa  deferentia 
ami  vesiculse  seminales,  and  of  the  accelerator  urinae  and  other 
muscles  of  the  urethra  ;  and  a  forcible  expulsion  of  semen  takes 
place,  over  which  the  mind  has  little  or  no  control,  and  which,  in 
cases  of  paraplegia,  may  be  unfelt.  Tfie  erection  of  the  penis, 
also,  as  already  explained  (p.  211),  appears  to  be  in  part  the  result 
<»f  a  reflex  contraction  of  the  muscles  by  which  the  veins  returning 
the  blood  from  the  penis  are  compressed.  The  involuntary  action 
<>/  the  uterus  in  expelling  its  contents  during  parturition,  is  also  of  a 
purely  reflex  kind,  dependent  in  part  upon  the  spinal  cord,  though 
in  part  also  upon  the  sympathetic  system:  its  independence  of 
the  brain  being  proved  by  cases  of  delivery  in  paraplegic  women, 
and  also  by  the  fact  that  delivery  can  take  place  whilst  the  patient 
is  under  the  influence  of  chloroform.  But  all  these  spinal  nerve- 
centres  are  intimately  connected,  both  structurally  and  physio- 
logically, one  with  another,  as  well  as  with  those  higher  en- 
cephalic centres,  without  whose  guiding  influence  their  actions 
may  become  disorderly  and  purposeless,  or  altogether  abrogated. 
Centre  for  Movements  of  Lymphatic  Hearts  of  Fro;/. — Volkmann 
has  shown  that  the  rhythmical  movements  of  the  anterior  pair  of 
lymphatic  hearts  in  the  frog  depend  upon  nervous  influence  derived 
from  the  portion  of  spinal  cord  corresponding  to  the  third  vertebra, 
and  those  of  the  posterior  pair  on  influence  supplied  by  the  portion 
•  if  cord  opposite  the  eighth  vertebra.  The  movements  of  the 
heart   continue,  though  the  whole  <»f  the  cord,  except  the  above 


582  THE  NERVOUS   SYSTEM.  [chap.  xvrn. 

portions,  be  destroyed;  but  on  the  instant  of  destroying  either  of 
these  portions,  though  all  the  rest  of  the  cord  be  untouched,  the 
movements  of  the  corresponding  hearts  eease.  What  appears  to  be 
thus  proved  in  regard  to  two  portions  of  the  cord,  may  be  inferred 
to  prevail  in  other  portions  also ;  and  the  inference  is  reconcilable 
with  most  of  the  facts  known  concerning  the  physiology  and 
comparative  anatomy  of  the  cord. 

Tone  of  Muscles. — The  influence  of  the  spinal  cord  on  the 
sphincter  ani  (centre  for  defoecation)  has  been  already  mentioned  (see 
al  x  »ve).  It  maintains  this  muscle  in  permanent  contraction,  so  that, 
except  in  the  act  of  defalcation,  the  orifice  of  the  aims  is  always  closed. 
This  influence  of  the  cord  resembles  its  common  reflex  action  in 
being  involuntary,  although  the  will  can  act  on  the  muscle  to  make 
it  contract  more,  or  may  inhibit  the  action  of  the  ano-spinal  centre 
so  as  to  permit  its  dilatation.  The  condition  of  the  sphincter  ani, 
however,  is  not  altogether  exceptional.  It  is  the  same  in  kind, 
though  it  exceeds  in  degree  that  condition  of  muscles  which  has 
been  called  tone,  or  passive  contraction  :  a  state  in  which  they 
always  when  not  active  appear  to  be  during  health,  and  in  which, 
though  called  inactive,  they  are  in  slight  contraction,  and  certainly 
are  not  relaxed,  as  they  are  long  after  death,  or  when  the  spinal 
cord  is  destroyed.  This  tone  of  all  the  muscles  of  the  trunk  and 
limbs  depends  on  the  spinal  cord,  as  the  contraction  of  the  sphincter 
ani  does.  If  an  animal  be  killed  by  injury  or  removal  of  the  brain 
the  tone  of  the  muscles  may  be  felt  and  the  limbs  feel  firm  as 
during  sleep  :  but  if  the  spinal  cord  be  destroyed,  the  sphincter 
ani  relaxes,  and  all  the  muscles  feel  loose,  and  flabby,  and  atonic, 
and  remain  so  till  rigor  mortis  commences.  This  kind  of  tone  must 
be  distinguished  from  that  mere  firmness  and  tension  which  it  is 
customary  to  ascribe,  under  the  name  of  tone,  to  all  tissues  that 
feel  robust  and  not  flabby,  as  well  as  to  muscles.  The  tone  pe- 
culiar to  muscles  has  in  it  a  degree  of  vital  contraction  :  that  of 
other  tissues  is  only  due  to  their  being  well  nourished,  and  there- 
fore compact  and  tense. 

All  the  foregoing  examples  illustrate  the  fact  that  the  spinal  cord 
is  a  collection  of  reflex  centres,  upon  which  the  higher  centres  act 
by  sending  down  impulses  to  set  in  motion,  to  modify  or  to  control 
them.  The  movements  or  other  })henomena  of  reflection  being 
as  it  were  the  function  of  the  ganglion  cells  to  set  in  action, 
after  an  afferent  impression  has  been   conveyed  to  them  by  the 


<  H\\:  XVIII.] 


STRUCTURE   OF   MEDULLA. 


5«3 


rior  nerve-trunks  in  connection  with  them.  The  extent  of 
the  resulting  movement  depends  upon  the  strength  of  the  stimulus, 
the  position  at  which  it  was  applied  as  well  as  upon  the  condi- 
tion of  the  uerve  cells;  the  connection  between  the  cells  being 
utimatc  that  a  series  of  coordinated  movements  may  result 
from  a  Bingle  stimulation,  first  of  all  affecting  one  celL  Whether 
the  cells  possess  as  well  the  power  of  originating  impulses  (automa- 
tism) is  doubtful,  but  this  is  possible  in  th<  of  vaso- 
cattm  which   are  situated  in  the  cord  (p.   192),  and  of 

>•  which  must  be  closely  related  to  them,  and  possibly  in  the 
of  the  centres  for  maintaining  the  tone  of  muscles. 


The  Medulla  Oblongata. 

The  medulla  oblongata  (tigs.  321,  522),  is  a  column  of  grey  and 
white  nervous  substance  formed  by  the  prolongation  upwards  of 
the  spinal  cord  and  connecting  it 
with  the  1  »rain. 

Structure.  —  The  grey  sub- 
stance which  it  contains  is  sitn- 
I  in  the  interior  and  variously 
divided  into  m  -  a  md  lamina? 
by  the  white  or  fibrous  substance 
which  is  arranged  partly  in  exter- 
nal columns,  and  partly  in  fasciculi 
traversing  the  central  grey  mat- 
fcer.  The  medulla  oblongata  is 
larger  than  any  part  of  the  spinal 
cord.  Its  columns  are  pyriform, 
enlarging  as  they  proceed  towards 
the  brain,  and  are  continuous 
with  those  of  the  spinal  Cord. 
:h  half  of  the  medulla,  there- 
fore, may  be  divided  into  three 
columns  or  tracts  of  fibres,  conti- 
nuous with  the  three  tracts  of 
which  each  half  of  the  spinal  cord 
is  made  up.  The  columns  are 
more    prominent    than    those    of 

the    spinal    cord,    and    separated    from   each    other    by    deeper 
grooves.      The    anterior,    continuous    with    the    anterior    columns 


Pi?.  321. —  Anterior  surface  of  the  pon* 
Varolii,  mvl   medulla   otloiw  I 
anterior  pvramid*  ;  b,  their  decussation ; 
<-,   c,    olivary    bodi  restifonn 

bodies  ;  e.  a'reifonn  fibres  ;  /,  fibres  de- 
scribe! by  Solly  as  passing  from  the 
anterior  column" of  the  cord  to  the  cere- 
bellum ;  .7,  anterior  column  of  the  spinal 
cor:  ral  column;   p,  pons  V«r 

rolii ;  i,  its  upper  fibres  ;  5,5,  roots  of 
the  fifth  pair  of  nerves. 


584 


THE  NEETOTJS   SYSTEM. 


[CHAT.   XVI II 


of  the  cord,  are  called  the  anterior  pyramids;  the  posterior, 
continuous  with  the  posterior  columns  of  the  cord,  and  comprising 
the  funiculus  cuneatus,  and  the  funiculus  of  Rolando  (fig.  323,  f.c, 
f.R.\  are  called  the  restiform  bodies.  On  the  outer  side  of  the 
anterior  pyramids  of  each  side,  near  its  upper  part,  is  a  small 
oval  mass  containing  grey  matter,  and  named  the  olivary  body ; 
and  at  the  posterior  part  of  the  restiform  column,  immediately  on 
each  side  of  the  posterior  median  groove,  continuous  with  the 
posterior  median  column  of  the  cord,  a  small  tract  is  marked 
off  by  a  slight  groove  from  the   remainder  of  the  restiform  body, 

and  called  the  posterior  pyramid  or 
fasciculus  gracilis.  The  restiform 
columns,  instead  of  remaining  parallel 
with  each  other  throughout  the  whole 
length  of  the  medulla  oblongata, 
diverge  near  its  upper  part,  and  by 
thus  diverging,  lay  open,  so  to  speak, 
a  space  called  the  fourth  ventricle, 
the  floor  of  which  is  formed  by  the 
grey  matter  of  the  interior  of  the 
medulla,  by  this  divergence  exposed. 
On  separating  the  anterior  pyra- 
mids, and  looking  into  the  groove 
between  them,  some  decussating 
fibres  of  the  lateral  columns  of  the 
cord  can  be  plainly  seen. 


Fig\  322.— Posterior  surface  of  the  pons 
J  arolii,  corpora  quadrigemina,  end 
■medulla  oblongata.  The  peduncles  of 
the  cerebellum  are  cut  short  at  the 
side,  a,  a,  the  upper  pair  of  corpora 
quadrigemina  ;  b,  b,  the  lower  ;  /,  f, 
superior  peduncles  of  the  cerebellum; 

c,  eminence  connected  with  the 
nucleus  of  the  hypoglossal  nerve; 
e,  that  of  the  glosso-pharyngeal 
nerve  ;   i,  that  of  the  vagus  nerve  ; 

d,  d,  restiform  bodies ;  p,  p,  poste- 
rior pyramids;  v,  v,  groove  in  the 
middle  of  the  fourth  ventricle,  end- 
ing below  in  the  calamus  scriptorius ; 
7,  7,  roots  of  the  auditory  nerves. 


Distribution    of    the    Fibres   of 

the  Medulla   Oblongata. 

The  anterior  pyramid  of  each  side, 
although  mainly  composed  of  continua- 
tions of  the  fibres  of  the  anterior  columns 
of  the  spinal  cord,  receives  fibres  from 
the  lateral  columns,  both  of  its  own  and 
the  opposite  side  ;  the  latter  fibres  form- 


ing almost  entirely  the  decussating- 
strands  which  are  seen  in  the  groove  between  the  anterior  pyramids.  Thus 
composed,  the  anterior  pj-ramidal  fibres  proceeding  onwards  to  the  brain 
are  distributed  in  the  following  manner  : — 

1.  The  greater  part  pass  on  through  the  Tons  to  the  Cerebrum.  A  por- 
tion of  the  fibres,  however,  running  apart  from  the  others,  joins  some  fibres 
from  the  olivary  body,  and  unites  with  them  to  form  what  is  called  the  oliva  nj 
fasciculus  or  fillet.     2.  A  small  tract  of  fibres  proceeds  to  the  cerebellum. 


rvm.]    STRUCTURE  OF   MEDULLA   OBLONGATA. 


58S 


A. 


Tlic  lateral  column  of  the  cord  on  each  side  of  the  medulla,  in  proceeding 
ipwards,  divides  into  three  parts,  outer,  inner,  and  middle,  which  arc  thus 
disposed  of  : — 1.  The  outer  fibres  (direct  cerebellar  tract)  go  with  the  resti- 
torm  trad  to  thi  cerebellum.    2.  The  middle  (crossed  pyramidal  tract)  de- 
cussate across  the  middle  line 

with  their  fellows,  and  form 
i  pari  of  the  anterior  pyra- 
mid of   the  opposite     side. 

3.    The    ii/in  r   paSS  OD  to  the 

cerebrum,  at  firsl  superfi- 
cially bul  afterwards  be- 
ueath  the  olivary  body  and 
the  arcuate  fibres,  and  then 
proceed  along  the  Moor  <»f 
the  fourth  ventricle,  on  each 
side,  under  the  name  of  the 
fasciculus  teres. 

The  posterior  column  of 
the  cord  is  represented  in 
the  medulla  by  the  posterior 
pyramid,  or  fasciculus  gra- 
cilis, which  is  a  continuation 
of  the  posterior  media)) 
column,  and  by  the  resti- 
form  body,  comprising  the 
funiculus  cuneatus  and  the 
funiculus  of  Rolando.  The 
fasciculus  gracilis  (fig.  323, 
f.g),  diverges  above  as  the 
1  'i'<  tader  clava  to  form,  one  on 
either  side,  the  lower  lateral 
boundary  of  the  fourth  ven- 
tricle, then  tapers  off.  and 
becomes  no  longer  traceable. 
The  funiculus  cuneatus.  or  the 
rest  of  the  posterior  column 
of  the  cord,  is  continued  up 
in  the  medulla  as  such  (fig. 
323,  f.c)  ;  but  soon,  in  addi- 
tion, between  this  and  the 
continuation  of  the  posterior 
nerve  roots,  appears  another 
tract  called  the  funiculus  of 
Rolando  (fig.  323,/.^).  High 
up,  the  funiculus  cuneatus  is 
covered  by  a  set  of  fibres 
(arcuate  fibres),  which  issue 
from  the  anterior  median 
fissure,  turn  upwards  over  the  anterior  pyramids  to  pass  directly  into  the 
corresponding  hemisphere  of  the  cerebellum,  being  joined  by  the  fibres 
of  the  direct  cerebellar  tract ;  the  funiculus  of  Rolando,  and  the  funiculus 
cuneatus.  although  appearing  to  join  them,  do  not  actually  do  so,  except  to 
a  partial  extent. 


Fit 


pin 


.323. — Posterior  view  of  the  medulla,  fourth  ventri- 
cle, and  mesencephalon  'natural  size),  p.  n,  line 
of  the  posterior  roots  of  the  spinal  nerves ; 
j'.m.f.,  posterior  median  fissure;  /.  ;/.,  funiculus 
gracilis  ;  cl.,  its  da  vis  ;  /.<•.,  funiculus  cuneatus  ; 
/./.'.,  funiculus  of  Rolando  ;  r.h.,  restiform  body  : 
c.8.,  calamus  scriptorius  ;  I,  section  of  ligula  or 
taenia ;  part  of  choroid  plexus  is  seen  beneath 
it;  l.r.,  lateral  recess  of  the  ventricle:  •'.., 
strife  aeusticiH  ;  if.,  inferior  fossa;  .^./..poste- 
rior fossa  ;  between  it  and  the  median  sulcus  is 
the  fasciculus  teres  ;  cbl.,  cut  surface  of  the  cere- 
bellar hemisphere  ;  n.il.,  central  or  grey  matter  ; 
s.m.v.,  superior  medullary  velum;  h*g.,  ligula  ; 
s.c.p.,  superior  cerebellar  peduncle  cut  longitudi- 
nally ;  <-/•.,  combined  section  of  the  three  cere- 
bellar peduncles;  c.q.8.,  c.q.i.,  corpora  quadri- 
gemina  (superior  and  inferior)  ;  //•.,  frtenulum  ; 
/.,  fibres  of  the  fillet  seen  on  the  surface  of  the 
tegmentum;  c,  crusti ;  /.</.,  lateral  groove; 
c.g.i.,  corpus  geniculum  interims;  th.,  posterior 
part  of  thalamus;  p.,  pineal  body.  The 
roman  numbers  indicate  the  corresponding 
cranial  nerves.     (E.  A.  Schiifer.) 


536 


THE  NERVOUS   SYSTEM. 


[chap.  xvm. 


Grey  matter  of  the  medulla. — To  a  considerable  extent  the  grey 
matter  of  the  medulla  is  a  continuation  of  that  in  the  spinal  cord, 
but  the  arrangement  is  somewhat  different. 


n.ZT. 


n-5ff~ 


S.G; 


The  displacement  of  the 
anterior  cornu  takes  place 
because  of  the  decussation  of 
a  large  part  of  the  -fibres  of 
the  lateral  columns  in  the 
anterior  pyramids  passing 
through  the  grey  matter  of 
the  anterior  cornu,  so  that 
the  caput  cornu  is  cut  off 
from  the  rest  of  the  grey 
matter,  and  is,  moreover,, 
pushed  backwards  by  the 
olivary  body,  to  be  men- 
tioned below.  It  lies  in  the 
lateral  portion  of  the  me- 
dulla, and  exists  for  a  time  as 
the  nucleus  lateralis  (fig.  324, 
/?/):  it  consists  of  a  reticulum 
of  grey  matter,  containing 
ganglion  cells  intersected  by 
white  nerve  fibres.  The  base 
of  the  anterior  cornu  is 
pushed  more  from  the  ante- 
rior surface,  and  when  the 
central  canal  opens  out  into 
the  fourth  ventricle,  forms 
a  collection  of  ganglion  cells, 
producing  the  eminence  of 
the  fasciculus  teres ;  from 
certain  large  cells  in  it  arise 
the  hypoglossal  nerve  (fig. 
325,  All.),  which  passes 
through  the  medulla,  and 
appears  between  the  olivary 
body  and  the  anterior  pyra- 
mids. 
In  the  funiculus  teres,  nearer  to  the  middle  line  as  well  as  to  the  surface,  is 
a  collection  of  nerve  cells  called  the  nucleus  of  that  funiculus  (fig.  325,  nt).  The 
grey  matter  of  the  posterior  cornu  is  displaced  somewhat  by  bands  of  fibres 
passing  through  it.  The  caput  cornu  appears  at  the  surface  as  the  funiculus 
of  Rolando,  whilst  the  cervix  cornu  is  broken  up  into  a  reticulated  structure 
which  is  displaced  laterally,  similar  in  structure  to  the  nucleus  lateralis. 
From  the  increase  of  the  base  of  the  posterior  cornu,  the  nuclei  of  the  funi- 
culus gracilis  and  funiculus  cuneatus  are  derived  (fig.  324,  n.g.  n.c),  and  out- 
side of  the  latter  is  an  accessory  nucleus  formed  (rig.  324,  n.c'  ).  Internally 
to  these  latter,  and  also  derived  from  the  cells  of  the  base  of  the  posterior 
cornu  and  appearing  in  the  floor  of  the  fourth  ventricle,  when  the  central 


Fig.  324. — Section  of  the  medulla  oblongata  in  the  region 

of  the  superior  pyramidal  decussation,  a.m./.,  ante- 
rior median  fissure ;  /.a.,  superficial  arciform 
fibres  emerging  from  the  fissure  :  />.y.,  pyramid  ; 
n.a.r.,  nuclei  of  arciform  fibres  ;  /.".,  deep  arei- 
form  becoming  superficial ;  o.,  lower  end  of  olivary 
nucleus ;  »./.,  nucleus  lateralis ;  f.r.,  formatio 
reticularis  ;  /.<7.2,  areiforni  fibres  proceeding  from 
the  formatio  reticularis  ;  ?.,  substantia  gelatinosa 
of  Rolando;  a.V..  ascending  root  of  fifth  nerve  ; 
n.c,  nucleus  cuneatus;  /'.'■'..  external  cuneate 
nucleus;  n.g.,  nucleus  gracilis;  f.g.,  nucleus  gra- 
cilis ;  p.m./.,  posterior  median  fissure;  c.c,  central 
canal  surrounded  by  grey  matter,  in  -which  are 
n.XI.,  nucleus  of  the  spinal  accessory,  and  n.XII., 
nucleus  of  the  hypoglossal ;  s.d.,  superior  pyramidal 
decussation.     (Sclrwalbe.)   (Modified  from  Quain.: 


CHAP.   Will.  ] 


STRUCTUKK   (»F    MEDULLA. 


587 


n.am 


canal    opens  are  t he   nuclei   of    the   spinal 

pharyngeal  nerv<  s.  In  the  apper  part  of  the  medulla  also,  to  the  outside  of 
these  three  auclei,  is  found  the  principal  auditory  nucleus,  All  the  above 
nuclei  appear  to  be  de- 
rived from  a  continua- 
tion of  the  ■-  rey  matter 
of  the  spinal  cord,  hut 
a  fresh  collection  of 
grey  matter  not 
sented  is  interpolated 
between  the  anterior 
pyramids  and  the  late- 
ral column,  contained 
within  the  olivary  pro- 
minence, the  wavy  line 
of  which  (corpus  den- 
tatum)  is  doubled  upon 
itself  at  an  angle  with 
the  extremities  directed 
upwards  and  inwards 
<ti'_r.  325.0).  There  may 
also  be  a  -mailer  col- 
lection of  grey  matter 
on  the  outer  and  inner 
side  of  the  olivary  nu- 
cleus known  as  acces- 
sory olivary  nuclei. 


n.ai 


Fi; 


,2_      g  r  the  medulla  oblongata  at  about  the  vu 

•„y  V  body.      f.l.a.,  anterior   median  fissure; 

n  ar.t  nucleus  arciformis  :  p.,  pyramid  ;  XII.,  bundle  of 
hvposrlossal  nerve  emerging  from  the  surface;  a*  ft, re 
is  seen  1  -<mrsin<r  between  the  pyi-amid  and  the  olivary 
nuclenfl  «  i  f. ••'•-..  external  arcifonn  fibres  ;»./..  nucleus 
laterals-  a  ,  arcif arm  fibres  passing  towards  restiform 
hodv  partlv  throuarh  the  substantia  gelatinosa,  .</..  partly 
superncial  to  the  ascending  root  of  the  fifth  nerve,  a.  v.; 

V  bundle  of  vagus  root  emerging  ;  f.r.,  formatio  reti- 
cularis ■  cr,  corpus  resttforme,  beginning  to  be  formed, 
chiefly  'by  axcifarm  fibres,  superficial  and  deep ;  ».e., 
nucleus  euneatus;  *.g.,  nucleus  gracilis  ;  /.attachment 
of  theb>ula  ;  f.».,  funiculus  solitanus  ;  n.X.,  n.  A .  .  CWO 
Darts  of  the  vagus  nucleus  :  /..AY/,  .hypoglossal  nucleus  ; 
n  1  nucleus  of  the  funiculus  teres  ;  ».«.,  nucleus  am- 
buTUons:  r., raphe;  A.,  continuation  of  the  anterior 
column  of  cord:  </,  ■■'■  accessory  olivary  ^mrdeusj  p.o., 
pedunculus  olivk     Schwalbe.    Modified  from  Uuam. 


Functions  of  the 
Medulla 
Oblongata. 
The  functions  of  the 

medulla  oblongata, 
like  those  of  the 
.spinal  cord,  may  be 
o  insidered  under  the 
heads  of;  i.  Con- 
duction :  2.  Trans- 
ference and  Reflec- 
tion :  and,  in  addition,  3.  Automatism. 

1.  In  conducting  impressions  the  medulla  oblongata  has  a  wider 
extent  of  function  than  any  other  part  of  the  nervous  system, 
since  it  is  obvious  that  all  impressions  passing  to  and  fro  between 
the  brain  and  the  spinal  cord  and  all  nerves  arising  below  the  pons, 
must  be  transmitted  through  it. 

2.  As  a  nerve-centre  by  which  impressions  are  transferred  or 
reflected,  the  medulla  oblongata  also  resembles  the  spinal  cord  ; 


588  THE   NERVOUS   SYSTEM.  [chap.  xvnr. 

the  only  difference  between  them  consisting  of  the  fact  that  many 
of  the  reflex  actions  performed  by  the  former  are  much  more 
important  to  life  than  any  performed  by  the  spinal  cord. 

Demonstration  of  Functions. — It  has  been  proved  by  re- 
peated experiments  on  the  lower  animals  that  the  entire  brain  may 
be  gradually  cut  away  in  successive  portions,  and  yet  life  may 
continue  for  a  considerable  time,  and  the  respiratory  movements 
be  uninterrupted.  Life  may  also  continue  when  the  spinal  cord  is 
cut  away  in  successive  portions  from  below  upwards  as  high  as  the 
point  of  origin  of  the  phrenic  nerve.  In  Amphibia,  the  brain 
has  been  all  removed  from  above,  and  the  cord,  as  far  as  the 
medulla  oblongata,  from  below ;  and  so  long  as  the  medulla  ob- 
longata was  intact,  respiration  and  life  were  maintained.  But  if, 
in  any  animal,  the  medulla  oblongata  is  wounded,  particularly  if 
it  is  wounded  in  its  central  part,  opposite  the  origin  of  the  pneu- 
mogastric  nerves,  the  respiratory  movements  cease,  and  the 
animal  dies  asphyxiated.  And  this  effect  ensues  even  when  all 
parts  of  the  nervous  system,  except  the  medulla  oblongata,  are 
left  intact. 

Injury  and  disease  in  men  prove  the  same  as  these  experiments 
on  animals.  Numerous  instances  are  recorded  in  which  injury  to 
the  medulla  oblongata  has  produced  instantaneous  death  :  and, 
indeed,  it  is  through  injur}'  of  it,  or  of  the  part  of  the  cord  con- 
necting it  with  the  origin  of  the  phrenic  nerve,  that  death  is 
commonly  produced  in  fractures  and  diseases  with  sudden  dis- 
placement of  the  upper  cervical  vertebrae. 

Special  Centres. 

(i.)  Respiratory. — The  centre  whence  the  nervous  force  for  the 
]  (reduction  of  combined  respiratory  movements  appears  to  issue  is 
in  the  interior  of  that  part  of  the  medulla  oblongata  from  which 
the  pneumogastric  nerves  or  Vagi  arise.  The  vagi  themselves 
indeed,  are  not  essential  to  the  respiratory  movements;  for  both 
may  be  divided  without  more  immediate  effect  than  a  retardation 
of  these  movements.  But  in  this  part  of  the  medulla  oblongata 
is  the  nerve-centre  whence  the  impulses  producing  the  respira- 
tory movements  issue,  and  through  which  impulses  conveyed  from 
distant  parts  are  reflected. 

The  Avide   extent  of  connection  which  belongs   to   the  medulla 


chap,  xviii.]  FUNCTIONS    OF    MEDULLA.  -,S<, 

oblongata  as  the  centre  of  the  respiratory  movements,  is  shown 
by  the  tact  that  impressions  by  mechanical  and  other  ordinary 
stimuli,  made  on  many  parts  of  the  external  or  internal  surfac  ■ 
of  the  body,  may  modify,  i.e.t  increase  or  diminish   the  rapidity  of 

respiratory  movements.  Thus  involuntary  respirations  aiv  ir. 
dliced  by  the  sudden  contact  of  cold  with  any  part  of  the  skin, 
as  in  dashing  cold  water  on  the  face.  Irritation  of  the  mucous 
membrane  of  the  no.se  produces  sneezing.  Irritation  in  the 
pharynx,  oesophagus,  stomach,  or  intestines,  excites  the  concurrence 
of  the  respiratory  movements  to  produce  vomiting.  Violent 
irritation  in  the  rectum,  bladder,  or  uterus,  gives  rise  to  a  con- 
current action  of  the  respiratory  muscles,  so  as  to  effect  the 
expulsion  of  the  fajecs,  urine,  or  foetus. 

(2)  Centre  for  Deglutition. — The  medulla  oblongata  appears  to 
be  the  centre  whence  are  derived  the  motor  impulses  enabling  the 
muscles  of  the  palate,  pharynx,  and  oesophagus  to  produce  the 
successive  co-ordinate  and  adapted  movements  necessary  to  the 
act  of  deglutition  (p.  296).  This  is  proved  by  the  persistence  of 
swallowing  in  some  of  the  lower  animals  after  destruction  of  the 
cerebral  hemispheres  and  cerebellum;  its  existence  in  anencepha- 
lous  monsters  ;  the  power  of  swallowing  possessed  by  the  marsupial 
embryo  before  the  brain  is  developed  :  and  by  the  complete  arrest 
of  the  power  of  swallowing  when  the  medulla  oblongata  is  injured 
in  experiments.  (3)  A  centre  by  which  the  movements  of  masti- 
cattonare  regulated  (p.  279).  (4)  Through  the  medulla  oblongata, 
chiefly,  are  reflected  the  impressions  which  excite  the  secretion  of 
saliva  (p.  286).  (5)  Cardio-inhiUtory  centre  for  the  regulation  of 
the  action  of  the  heart,  through  the  pneumogastrics  and  probably 
also,  the  accelerating  fibres  of  the  sympathetic  (p.  157).  (6)  The 
chief  vasomotor  centre.  From  this  centre  arise  fibres  which,  pass- 
ing down  the  spinal  cord,  issue  with  the  anterior  roots  of  the 
spinal  nerves,  and  enter  the  ganglia  and  branches  of  the  sympa- 
thetic system,  by  which  they  are  conducted  to  the  blood-vessels 
(p.  192 J.  (7)  Cilio-spiiwl  centre  for  the  regulation  of  the  iris, 
and  other  plain-fibred  muscles  of  the  eye.  (8  and  9)  Centres  or 
ganglia  of  the  special  senses  of  hearing  and  taste,  (10)  The  centre 
for  speech,  i.e.,  the  centre  by  which  the  various  muscular  move- 
ments concerned  in  speech  are  co-ordinated  or  harmonised,  (n) 
Centre  by  which  the  many  muscles  concerned  in  vomiting  are  liar- 


590  THE    NERVOUS    SYSTEM.  [chap.  xvii.. 

monised.  (12)  The  so-called  diabetic  centre,  or,  in  other  words, 
the  grey  matter  in  the  medulla  oblongata  which,  being  irritated, 
causes  glycosuria  (p.  351),  is  probably  the  vasomotor  centre  :  and 
this  peculiar  result  of  its  stimulation  is  merely  due  to  vasomotor 
changes  in  the  liver. 

Though  respiration  and  life  continue  while  the  medulla  oblongata 
is  perfect  and  in  connection  with  the  respiratory  nerves,  yet,  when 
all  the  brain  above  it  is  removed,  there  is  no  more  appearance  of 
sensation,  or  will,  or  of  any  mental  act  in  the  animal,  the  subject 
of  the  experiment,  than  there  is  when  only  the  spinal  cord  is  left. 
The  movements  are  all  involuntary  and  unfelt  ;  and  the  medulla 
oblongata  has,  therefore,  no  claim  to  be  considered  as  an  organ  of 
the  mind,  or  as  the  seat  of  sensation  or  voluntary  power.  These 
are  connected  with  parts  to  be  afterwards  described. 

Pons  Varolii. 

Structure. — The  meso-cephalon,  or  pons  Varolii  (vi,  fig.  326), 
is  composed  principally  of  tranverse  fibres  connecting  the  two 
hemispheres  of  the  cerebellum,  and  forming  its  principal  transverse 
commissure.  But  it  includes,  interlacing  with  these,  numerous 
longitudinal  fibres  which  connect  the  medulla  oblongata  with  the 
cerebrum,  and  transverse  fibres  which  connect  it  with  the  cere- 
bellum. Among  the  fasciculi  of  nerve-fibres  by  which  these 
several  parts  are  connected,  the  pons  also  contains  abundant  grey 
or  vesicular  substance,  which  appears  irregularly  placed  among 
the  fibres,  and  fills  up  all  the  interstices. 

Functions. — The  anatomical  distribution  of  the  fibres,  both 
transverse  and  longitudinal,  of  which  the  pons  is  composed,  is 
sufficient  evidence  of  its  functions  as  a  conductor  of  impressions 
from  one  part  of  the  cerebro-spinal  axis  to  another.  Concerning  its 
functions  as  a  nerve-centre,  little  or  nothing  is  certainly  known. 

Crura  Cerebri. 

Structure. — The  crura  cerebri  (in,  fig.  326),  are  principally 
formed  of  nerve-fibres,  of  which  the  inferior  or  more  superficial 
(crusta)  are  continuous  with  those  of  the  anterior  pyramidal  tracts 
of  the  medulla  oblongata,  and  the  superior  or  deeper  fibres  (tegmen- 
tum) with  the  lateral  and  posterior  pyramidal  tracts,  and  with  the 


chat.  xvm. .  THE   CRURA    CEREBRI, 


59* 


olivarv  fasciculus.  Besides  these  fibres  from  the  medulla  oblongata, 
arc  others  from  the  cerebellum  ;  and  some  of  the  latter  as  well  as 
a  part  of  the  fibres  derived  from  the  lateral  tract  of  the  medulla 

oblongata,  decussate  acr<  SS  the  middle  line. 


Pig.  326. — Base  of  the  brain.  1,  superior  longitudinal  fissure ;  2,  2',  2",  anterior  cerebral 
lobe;  3,  fissure  of  Sylvias,  between  anterior  and  4,  4',  4",  middle  cerebral  lobe;  s,  5', 
posterior  lobe ;  6,  medulla  oblongata ;  the  figure  is  in  the  right  anterior  pyramid  ; 
7,  8,  9,  10,  the  cerebellum  ;  -f ,  the  inferior  vermiform  process.  The  figures  from  I.  to 
IX.  are  placed  against  the  coirespondinsr  cerebral  nerves  ;  III.  is  placed  on  the  right 
crus  cerebri.  VI.  and  VII.  on  the  pons  Varolii  ;  X.  the  first  cervical  or  suboccipital 
nerve.     (Allen  Thomson).    £. 

Each  crus  cerebri  contains  among  its  fibres  a  mass  of  grey  sub- 
stance, the  locus  niger. 

Functions. — With  regard  to  their  functions,  the  crura  cerebri 
may  be  regarded  as.  principally,  conducting  organs  :  the  cr.usta  con- 
ducting motor  and  the  tegmentum  sensory  impressions.  As  nerve- 
centres  they  are  probably  connected  with  the  functions  of  the  third 
cerebral  nerve,  which  arises  from  the  locus  niger^  and  through 
which  are  directed  the  chief  of  the  numerous  and  complicated 


592 


THE    NERVOUS    SYSTEM. 


[CHAP    XVIK. 


movements  of  the  eyeball.     The   crura  cerebri  arc  also  in  all  pro- 
bability connected  with   the    co-ordination    of   other    movement* 


Y\cr,  327. — 1>  insert  Ion  of  bra  in,  from  .  exposing  iht  lateral  fourth,  and  fifth  ventricles  with 

the  surrounding  parts.  A. — 0.  anterior  part,  or  genu  of  corpus  eallosum:  b,  corpus 
striatum  ;  b',  the  corpus  striatum  of  left  side,  dissected  so  as  to  expose  its  grey  sub- 
stance ;  ''.  points  by  a  line  to  the  ttenia  semicircularis  ;  d,  optic  thalamus  ;  e,  anteriu: 
pillars  of  fornix  divided  ;  below  they  are  seen  descending  in  front  of  the  third  ventricle, 
and  between  them  is  seen  part  of  the  anterior  commissure  :  in  front  of  the  letter  i- 
seen  the  slit-like  fifth  ventricle,  between  the  two  lamina'  of  the  septum  lucidum  ;  /, 
soft  or  middle  commissure ;  g  is  placed  in  the  posterior  part  of  the  third  ventricle ; 
immediately  behind  the  latter  are  the  posterior  commissure  (just  visible)  and  the 
pineal  gland,  the  two  crura  of  which  extend  forwards  along  the  inner  and  upper 
margins  of  the  optic  thalami ;  h  and  i,  the  corpora  quadrigemina  ;  k,  superior  cms  of 
cerebellum  ;  close  to  k  is  the  valve  of  Yieussens,  which  has  been  divided  so  as  to  ex- 
pose the  fourth  ventricle  ;  J,  hippocampus  major  and  corpus  fimbriatum,  or  taenia 
hippocampi ;  m,  hippocampus  minor;  »,  eminentia  collaterals ;  0,  fourth  ventricle: 
/>,  posterior  surface  of  medulla  oblongata  ;  r,  section  of  cerebellum  :  .«,  upper  part  of 
left  hemisphere  of  cerebellum  exposed  by  the  removal  of  part  of  the  posterior  een 
lobe.     ^Hirschfeld  and  Leveille.) 

besides  those  of  the  eye,  as  either  rotatory  (p.  599)  or  disorderly 
movements  result  after  section  of  either  of  them. 


Corpora  Quadrigemina. 

The  corpora  quadrigemina  (from  which,  in  function,  the  covj 
ueniculata  are    not    distinguishable),   are    the  homologues  of  the 


lp.  xviii.]     FUNCTIONS    "I  ORA    QUADRIGEMINA.      5 

•    •  bnphibia,  and  Fishes,  and   maj  be  regarded 

principal  nerve  for  the  -  Jit. 

Functions. — (1)  The    exper  of   Flourens,    Longet,  and 

Hertwig,  show  that  removal  of  the  1  quadrigemina  wholly 

the  power  of  seeing;    and   <li-  d  which  they  arc 

uised  are   usually  accompanied  by  blindness.     Atrophy  of 

them  is  also  often  a  consequence  of  atrophy  of  the  1 3  es.    I  »•  struction 

of  the  corpora  quadrigemina  (or  of  one  optic  lobe  in  bin 
produces  blind  the  opposite  eye.     This!  sight  is  the 

only  apparent   injury  of  sensibility  sustained  by  the  removal  of 
the    corpora   quadrigemina       Tl.       2     removal    of  one   of  them 
affects  the  movements  of  the  body,  so  that  animala  rotate,  as  af) 
-    n  of  the  crua  cerebri,  only  more  Blowly:  but  this  maybe 
3E   ind  partial  l<  88  1  :   sight.     (31  The  more  evident 
1  direct  influence  is  that  produced  <>n  the  iris.     It  contra 
wlu-n  the  corpora  quadrigemina  are  irritated  :  it  is  always  dilated 
when  tla-y  are  removed:  bo  that  they  may  he  regarded,  in  some 
measure  at  least,  aa  the  nervous  centn  -  gov<  ming  its  movemei 
and  adapting  them  to  the  impn  derived  from  the  retina 

_;i    the    optic    nerves  and  tracts.      (4)  The   centre   for    the 
-ordination  of  the  movementa  of  the  eyes  is  also  contained  in 

i      3   centre  is  closely     se     iated  with  that  for  contract 
the  pupil,  and  so  it  follows  that  contraction  or  dilatation  follows 
d  certain  definite  ocular  movementa 


Corpora  Striata  and  Optic  Thalami. 

Structure. — (1.)  The  corpora  striata  are  situated  in  front  <f 
the  optic  thalami,  partly  within  and  partly  without  the  lateral 
ventricle.     Each  corpus  .striatum  consists  of  two  par-. 

(a.)  Intraventricular  portion  (caudate  nucleus)  is  conical  in 
shape,  with  the  base  of  the  cone  forwards;  it  consists  of  grey 
matter,  with  whit.  nee  in  its  centre,  which   comes  from  the 

onding    cerebral  peduncle.     (6.)   Extraventricular   porti 
{lenticular  nm  3  se]  arated  from  the  other  portion  by  a  la; 

of  white  material.  It  is  seen  on  section  of  the  hemisphere.  Eta 
horizontal  section  is  wider  in  the  centre  than  at  the  end.  On  the 
outside  is  the  grey  lamina  (daustrum). 

n  the  corpus   striatum  and  optic  thalamus  is  the  ta 

k  q 


594  THE    NERVOUS    SYSTEM.  [chap,  xviii. 

semicircularis,  a  semi-transparent  band  which  is  continued  back 
into  the  white  substance  of  the  roof  of  the  descending  horn  of  the 
ventricle. 

(2.)  The  Optic  Thalami  are  oval  in  shape,  and  rest  upon  the 
crura  cerebri.  The  upper  surface  of  each  thalamus  is  free,  and  of 
white  substance,  it  projects  into  the  lateral  ventricle.  The  posterior 
surface  is  also  white.  The  inner  sides  of  the  two  optic  thalami 
are  in  partial  contact,  and  are  composed  of  grey  material  un- 
covered by  white,  and  are,  as  a  rule,  connected  by  a  transverse 
portion. 

Functions. — The  two  ganglia,  the  Corpus  Striatum,  and  Optic 
Thalamus,  are  placed  between  the  cerebral  convolutions  and  the 
eras  cerebri  of  the  same  side.  It  is  probable  that  although  some  of 
the  fibres  of  the  eras  pass  without  interruption  into  the  cerebrum, 
the  majority  of  the  fibres  pass  into  these  ganglia  first  of  all  the 
lower  fibres  (crusta)  into  the  corpus  striatum,  and  the  upper 
(tegmentum)  into  the  optic  thalamus,  and  then  out  into  the  cere- 
brum. From  the  position  of  these  bodies,  it  would  be  reasonable 
to  suppose  that  they  were  interposed  in  function  between  the 
operation  of  the  will  on  the  one  hand,  and  on  the  other  with  the 
sensori-motor  apparatus  below  them,  and  it  is  believed  that  this 
is  the  case,  although  the  evidence  is  not  exact  :  the  theory  that 
the  corpus  striatum  is  the  motor  ganglion,  and  that,  when  injured, 
the  communication  between  the  will  and  the  muscles  of  one  half 
of  the  body  is  broken  (hemiplegia),  being  supported  by  many 
pathological  facts  and  plrysiological  experiments,  and  generally 
received  by  pathologists.  It  is  found  that  the  cerebral  functions 
are  as  a  rule  unimpaired.  In  the  same  way  the  evidence  that 
the  optic  thalamus  is  the  sensory  ganglion  depends  upon  similar 
observations,  that  when  injured  or  destroyed,  sensation  of  the 
opposite  side  of  the  body  is  impaired  or  lost.  In  both  cases,  the 
parts  paralysed  are  on  the  opposite  side  to  the  lesions,  the  decus- 
sation of  both  sets  of  fibres  taking  place,  as  we  have  seen,  below 
the  ganglia.  It  is  a  fact,  however,  that  many  experiments  and 
pathological  observations  are  opposed  to  the  above  theory,  which 
must  therefore  be  received  with  caution. 


CHAP.   Will.] 


THE    CEREBELLUM 


595 


The    Cerebellum. 

The  Cerebellum  (7,  8,  9,  10,  fig.  326),  is  composed  of  an   elon 
gated  central  portion   called   the  vermiform   proa  and  two 

hemispheres.  Each  hemisphere  is  connected  with  its  fellow,  not 
only  by  means  of  the  vermiform  processes,  bul  also  by  a  bundle  of 
fibres  called  the   middle  crus  or  peduncU  (the    latter  forming  the 


Biff.  328.—  Cerebellum  in  section  and  of  fourth   ventricle,  with  the  neighbouring   parts,     r, 
median  groove  of  fourth  ventricle,  ending  below  in  the  calamus  ,  with  the 

longitudinal  eminences  formed  by  the  /  ntes,  one  on  each  side:  2,  the  same 

groove,  at  the  place  where  the  white  streaks  of  the  auditory  nerve  emerge  from  it  to 
cross  the  floor  of  the  ventricle  ;  3,  inferior  crus  or  peduncle  of  the  cerebellum,  formed 
by  the  restiform  body  ;  4,  posterior  pyramid  ;  above  this  is  the  calamus  Bcriptorius  ; 

5,  -uperior  crus  of  cerebellum,  or  processus  e   cerebello  ad  cerebrum  (or  ad  tee 

6,  6,  fillet  to  the  side  of  the  crura  cerebri ;  7,  7,  lateral  grooves  of  the  crura  cerebri  ; 
8,  corpora  quadrigemina.     (From  Sappey  after  Hirschfeld  and  Leveillc  . 


greater  part  of  the  pons  Varolii),  while  the  superior  crura  with  the 
valve  of  Vieussens  connect  it  with  the  cerebrum  (5,  fig.  328),  and 
the  infi  rior  crura  (formed  by  the  prolonged  restiform  bodies)  con- 
nect it  with  the  medulla  oblongata  (3,  fig.  328). 

Structure. — The  cerebellum  is  composed  of  white  and  grey 
matter,  the  latter  being  external,  like  that  of  the  cerebrum,  and 
like  it,  infolded,  so  that  a  larger  area  may  be  contained  in  a  given 
space.  The  convolutions  of  the  grey  matter,  however,  are  arranged 
after  a  different  pattern  as  shown  in  fig.  328.  Eesides  the  grey 
substance  on   the   surface,  there  is,  near  the  centre  of  the  white 

Q  Q  2 


596  THE    NERVOUS    SYSTEM.  [chap,  xviii. 

substance  of  each  hemisphere,  a  small  capsule  of  grey  matter  called 
the  corpus  dentatum  (fig.  329.  cd),  resembling  very  closely  the 
corpus  dentatum  of  the  olivary  body  of  the  medulla  oblongata  (fig. 
324,  0). 

If  a  section  be  taken  through  the  cortical  portion  of  the  cere- 


Fig.  329. —  Outline  sketch  of  a  section  of  the  cerebellum,  shouting  the  corpus  dentatum.     The 

section  has  been  carried  through  the  left  lateral  part  of  the  pons,  so  as  to  divide  the 
superior  peduncle  and  pass  nearly  through  the  middle  of  the  left  cerebellar  hemi- 
sphere. The  olivary  body  has  also  been  divided  longitudinally  so  as  to  expose  in 
section  its  corpus  dentatum.  cr,  eras  cerebri;  /,  fillet;  </.  corpora  quadi'igemina ; 
s Pi  superior  peduncle  of  the  cerebellum  divided;  m  p,  middle  peduncle  or  lateral 
part  of  the  pons  Varolii,  with  fibres  passing  from  it  into  the  white  stem  ;  a  >■,  continu- 
ation of  the  white  stem  radiating  towards  the  arbor  vitae  of  the  folia  :  c  '/,  corpus 
dentatum;  o,  olivary  body  with  its  corpus  dentatum;  p,  anterior  pyramid.  Allen 
Thomson,.     -'. 

bellum,  the  following  distinct  layers  can  be  seen  (fig.  330)  by  mi- 
croscopic examination. 

(1.)  Immediately  beneath  the  pia  mater  (p  m)  is  a  layer  of  con- 
siderable thickness,  which  consists  of  a  delicate  connective  tissue, 
in  which  are  scattered  several  spherical  corpuscles  like  those  of 
the  granular  layer  of  the  retina,  and  als<>  an  immense  number  of 
delicate  fibres  passing  up  towards  the  free  surface  and  branching 
as  they  go.  These  fibres  are  the  processes  <  >f  the  cells  of  Purkinje. 
(2.)  The  Cells  of  Purkinje  (  p).  These  are  a  single  layer  of  branched 
nerve-cells,  which  give  oft' a  single  unbranched  process  downwards, 
and  numerous  processes  up  into  the  external  layer,  some  of  which 
become  continuous  with  the  scattered  corpuscles.  (3.)  The  granu- 
lar layer  (.</),  consisting  of  immense  numbers  of  corpuscles  closely  re- 
sembling those  of  the  nuclear  layers  of  the  retina.  (4.)  Nerve  fibre 
layer  (/).  Bundles  of  nerve-fibres  forming  the  white  matter  of 
the  cerebellum,  which,  from  its  branched  appearance  has  been 
named  the  "arbor  vitae." 

Functions. — The  physiology  of  the  Cerebellum  may  be  con- 


CHAP.   .Will. 


FUNCTIONS    OF    CEREBELL1  M 


597 


/"" 


j,  in 


Bidered  in   its  relation   to  sensation,   voluntary   motion,   and  the 
instincts  or  higher  faculties  of  the  mind.     Its  supposed  functions, 

like  these  of  even 

other  part  of  the 
nervous  system. 
have  been  deter 
mined  by  physio 
Logical  experiment, 
by  pathological  ob- 
servation and  by 
its  comparative  an- 
atomy. 

(i.)  It   is   itself 
insensible  to  irrita 
tion,   and  may  be 

all  cut  away  with- 
out eliciting  signs 
of  pain  (Longet). 
Its  removal  or  dis- 
organization by 
disease  is  also  gene- 
rally unaccompani- 
ed by  loss  or  dis- 
order of  sensibility  : 
animals  from  which 
it  is  removed  can 
smell,  see,  hear, 
and  feel  pain,  to 
all  appearance,  as 
perfectly  as  before 
(Flourens ;  Magen- 
die).  Yet,  if  any 
of  its  crura  be 
touched,  pain  is 
indicated  ;  and,  if 
the  restiform  tracts 
of  the  medulla  ob- 
longata be  irrita- 
ted, the  most  acute- 


J>o<o.«r" 


!^°?&^& 


s$# 


'3 

COo' 


o.S'&^&ite'* 


mm^mm 


/ 


Fig.  330. — Vertical  section  of  dog's  cerebellum  :  p  vi,  pia  mater  ; 
p,  corpuscles  of  Purkinje,  which  are  branched  nerve-cells 
lying  in  a  single  layer  anil  sending-  single  processes  down- 
wards and  more  numerous  ones  upwards,  which  branch 
continuously  and  extend  through  the  deep  "molecular 
layer  "  towards  the  free  surface  ;  g,  dense  layer  of  gangli- 
onic corpuscles,  closely  resembling  nuclear  layers  of  retina  ; 
/,  layer  of  nerve-fibres,  with  a  few  scattered  ganglionic 
corpuscles.  This  last  layer  (./"./')  constitutes  part  of  the 
white  matter  of  the  cerebellum,  while  the  layers  between 
it  and  the  free  surface  are  grey  matter.  (Klein  and  Noble 
Smith. 


cjqS  THE    NERVOUS    SYSTEM.  [.hap.  xviii. 

suffering  appears  to  be  produced.  So  that,  although  the  restiform 
tracts  of  the  medulla  oblongata,  which  themselves  appear  so 
sensitive,  enter  the  cerebellum,  it  cannot  be  regarded  as  a  prin- 
cipal organ  of  sensation. 

(2.)  Co-ordination  of  Movements. — In  reference  to  motion,  the 
experiments  of  Longet  and  many  others  agree  that  no  irritation 
of  the  cerebellum  produces  movement  of  any  kind.  Remarkable 
results,  however,  are  produced  by  removing  parts  of  its  substance. 
Flourens  (whose  experiments  have  been  confirmed  by  those  of 
Bouillaud,  Longet,  and  others )  extirpated  the  cerebellum  in  birds 
by  successive  layers.  Feebleness  and  want  of  harmony  of  mus- 
cular movements  were  the  consequence  of  removing  the  superficial 
layers.  When  he  reached  the  middle  layers,  the  animals  became 
restless  without  being  convulsed  ;  their  movements  were  violent 
and  irregular,  but  their  sight  and  hearing  were  perfect.  By  the 
time  that  the  last  portion  of  the  organ  was  cut  away,  the  animals 
had  entirely  lost  the  powers  of  springing,  flying,  walking,  standing, 
and  preserving  their  equilibrium.  When  an  animal  in  this  state 
was  laid  upon  its  back,  it  could  not  recover  its  former  posture, 
but  it  fluttered  its  wings,  and  did  not  lie  in  a  state  of  stupor  ;  it 
saw  the  blow  that  threatened  it,  and  endeavoured  to  avoid  it. 
Volition  and  sensation,  therefore,  were  not  lost,  but  merely  the 
faculty  of  combining  the  actions  of  the  muscles ;  and  the  endea- 
vours of  the  animal  to  maintain  its  balance  were  like  those  of  a 
drunken  man. 

The  experiments  afforded  the  same  results  when  repeated  on 
all  classes  of  animals ;  and  from  them  and  the  others  before 
referred  to,  Flourens  inferred  that  the  cerebellum  belongs  neither 
to  the  sensory  nor  the  intellectual  apparatus  ;  and  that  it  is  not 
the  source  of  voluntary  movements,  although  it  belongs  to  the 
motor  apparatus;  but  is  the  organ  for  the  co-ordination  of  the 
voluntary  movements,  or  for  the  excitement  of  the  combined  action 
of  muscles. 

Such  evidence  as  can  be  obtained  from  cases  of  disease  of  this 
organ  confirms  the  view  taken  by  Flourens  ;  and,  on  the  whole,  it 
gains  support  from  comparative  anatomy ;  animals  whose  natural 
movements  require  most  frequent  and  exact  combinations  of  mus- 
cular actions  being  those  whose  cerebella  are  most  developed  in 
proportion  to  the  spinal  cord. 


i  hap.  xviii.  POB(  BO    tfOVEM&N  I  8. 

rille  supposed  that  the  cerebellum  is  the  organ  of  muscular 
- ..  the  organ  by  which  the  mind  acquires  that  knowledge  of 
actual  -rate  and  position  of  the  muscles  which  is  essentia]  to  * 
of  the  will  upon  them  ;  and  it   must  be  admitted  that  all 
the  facte  just  referred  to  are  as  well  explained  on  this  hypotln 

"ii  that  of  the  cerebellum  being  the  organ  for  combining  m< 
ments.  A  harmonious  combination  of  muscular  actions  must 
depend  as  much  on  the  capability  of  appreciating  the  condition  of 
the  muscles  with  regard  to  their  tension,  and  to  the  force  with 
which  they  are  contracting,  as  on  the  power  which  any  special 
nerve-centre  may  possess  of  exciting  them  to  contraction.  And  it 
is  because  the  power  of  such  harmonious  movement  would  be 
equally  lost,  whether  the  injury  to  the  cerebellum  involved  injury 
to  the  seat  of  muscular  sense,  or  to  the  centre  for  combining  mus- 
cular actions,  that  experiments  on  the  subject  afford  no  proof  in 
<»ne  direction  more  than  the  other. 

The  theory  once   believed,  that  the  cerebellum   is  the  organ  of 
—  ion,  has  been  long  disproved. 

Forced  Movements. — The  influence  of  each  half  of  the  cere- 
bellum is  directed  to  muscles  on  the  opposite  side  of  the  body  j 
and  it  would  appear  that  for  the  right  ordering  of  movements,  the 
actions  of  its  two  halves  must  be  always  mutually  balanced  and 
adjusted.  For  if  one  of  its  crura,  or  if  the  pons  on  either  side  of 
the  middle  line,  be  divided,  so  as  to  cut  off  from  the  medulla 
oblongata  and  spinal  cord  the  influence  of  one  of  the  hemispheres 
of  the  cerebellum,  strangely  disordered  movements  ensue  (forced 
movements).  The  animals  fall  down  on  the  side  opposite  to  that 
on  which  the  cms  cerebelli  has  been  divided,  and  then  roll  over 
continuously  and  repeatedly;  the  rotation  being  always  round  the 
long  axis  of  their  bodies,  and  generally  from  the  side  on  which  the 
injury  has  been  inflicted.  The  rotations  sometimes  take  place  with 
much  rapidity  :  as  often,  according  to  Magendie.  as  sixty  times 
in  a  minute,  and  may  last  for  several  days.  Similar  movements 
have  been  observed  in  men  ;  as  by  Serres  in  a  man  in  whom  there 
was  apoplectic  effusion  in  the  right  cms  cerebelli  :  and  by  Bel- 
homme  in  a  woman,  in  whom  an  I  on  the  left  cms. 

They  may,  parhaps,  be  explained  by  assuming  that  the  division  or 
injury  of  the  cms  cerebelli  produces  paralysis  or  imperfect  and 
disorderly  movements  of  the  opposite  side  of  the  body  :  the  animal 


600  THE    NERVOUS    SYSTEM.  [hap.  xviii. 

fulls,  and  then,  struggling  with  the  disordered  side  on  the  ground, 
and  striving  to  rise  with  the  other,  pushes  itself  over;  and  bo 
again  and  again,  with  the  same  act,  rotates  itself.  Such  move- 
ments cease  when  the  other  cms  cerebelli  is  divided  ;  but  probably 
only  because  the  paralysis  of  the  body  is  thus  made  almost  com- 
plete. Other  varieties  of  forced  movements  have  been  observed, 
especially  those  named  "circus  movements/'  when  the  animal 
operated  upon  moves  round  and  round  in  a  circle  ;  and  again  those 
in  which  the  animal  turns  over  and  over  in  a  series  of  somersaults. 
Nearly  all  these  movements  may  result  on  section  of  one  or  other 
of  the  following  parts  :  viz.  crura  cerebri,  medulla,  pons,  cere- 
bellum, corpora  quadrigemina,  corpora  striata,  optic  thalami,  and 
even,  it  is  said,  of  the  cerebral  hemispheres. 


The  Cerebrum. 

The  Cerebrum  (composed  of  two  so-called  Cerebral  hemispheres) 
is  placed  in  connection  with  the  Pons  and  Medulla  oblongata  by  its 
two  crura  or  peduncles  (III.  fig.  326)  :  it  is  connected  with  the 
cerebellum  by  the  processes  called  superior  crura  of  the  cerebellum, 
or  processus  a  cerebello  acl  testes,  and  by  a  layer  of  grey  matter,  called 
the  valve  of  Vieussens,  which  lies  between  these  processes,  and 
extends  from  the  inferior  vermiform,  process  of  the  cerebellum  to  the 
corpora  quadrigemina  of  the  cerebrum.  These  parts,  which  thus 
connect  the  cerebrum  with  the  other  principal  divisions  of  the 
cerebro-spinal  system  may,  therefore,  be  regarded  as  the  con- 
tinuation of  the  cerebro-spinal  axis  or  column;  on  which,  as  a 
kind  of  offset  from  the  main  nerve-path,  the  cerebellum  is  placed  - 
and  on  the  further  continuation  of  which  in  the  direct  line,  is 
placed  the  cerebrum  (fig.  331). 

The  Cerebrum  is  constructed,  like  the  other  chief  divisions  of 
the  cerebro-spinal  system,  of  grey  (vesicular  and  fibrous)  and  white 
(fibrous)  matter ;  and,  as  in  the  case  of  the  Cerebellum  (and  unlike 
the  spinal  cord  and  medulla  oblongata),  the  grey  matter  {cortex)  is 
external,  and  forms  a  capsule  or  covering  for  the  white  substance. 
For  the  evident  purpose  of  increasing  its  amount  without  undue 
occupation  of  space,  the  grey  matter  is  variously  infolded  so  as  to 
form  the  cerebral  convolutions. 


CUM'.    Will. 


THE    <  EREBKT'M 


601 


(      volution*  of  the  Cerebrum, — For  conv< 

if  the  brain  has  been  divided  into  five  lobes  (Gratiolet). 
i.  Frontal    V.  i  -    ^33),  limited  behind  by  the  fissui  lando 

nd  beneath  by  tl  5;  Its  a  rface  sonsiste 

«>f  three  main  convolutions,  which  a  simately  horizontal  in  dire 

ami  are  broken  up  into  mini  I 


Fig.  J31.— J  .  is  .-.-on  from  the  right  side.     3.     The  pa: 

represented  as  separated  from  one  another  somewhat  more  than  natui 
their  connections.    A,   cerebrum :  /,  .7.  ft,  its  anterior,  middle,  and  posterior  lobes; 
*-,  fissure  of  Sylvius  :  B.  cerebellum  :  C,  pons  Varolii  :  D.  medulla  oblongata  :  n,  ped- 
uncles  of  the  cerebrum  ;  b,  • .  d,  superior  middle,  and  inferior  peduncles  of  the  cere- 
bellum.    (From  Quain. 


superior,  middle,  and  inferior  frontal  convolutions.  In  addition,  the  f: 
lobe  contains,  at  it-  posterior  part,  a  convolution  which  run*  up- 
almost    vertically  ("ascending  frontal "), and  is  bounded   in  front  by  a 

termed  the  praecentral,  behind  by  that  of  Rolando. 

2.  Parietal  (P.).  This  lobe  is  bounded  in  front  bythe  fissure  of  Rolando, 
behind  hy  the  external  perpendicular  fissure  (parietooccipital  >.  and  below 
by  the  nVure  of  Sylvius.  Behind  the  fissure  of  Rolando  is  t:  *  mding 
parietal"  convolution,  which  swells  out  at  its  upper  end  into  what  is  termed 

-  nperior  parietal  lobule.  The  superior  parietal  lobule  i-  separated  from 
the  inferior  parietal  lobule  by  the  intra-parietal  sulci;-.  The  inferior 
parietal  lobule  (pli  courbe)  is  situated  at  th<  r  and  upper  end  of  the 

Sylvias;  it  <.      iistE    E  (//)  an  anterior  part  (supra-marginal  con- 
volution >  which  hooks  round  the  end  of  the  I  Sylvius,  and  joins  the 
superior  temporal   convolution,  and  a  posterior  part  (6)   (angular  g] 
which  hooks  round  into  the  middle  temporal  convolution, 

3.  Trmporo-^pkenoidal   (T.).   contain-    three   well-markel   convolution-. 


602 


THE  NERVOUS  SYSTEM. 


[chap,  xvii  r. 


parallel  to  each  other,  termed  the  superior,  middle,  and  inferior  temporal. 
The  superior  and  middle  are  separated  by  the  parallel  fissure. 

4.  Occipital  (0.).  This  lobe  lies  behind  the  external  perpendicular  or 
parieto-oecipital  fissure,  and  contains  three  convolutions,  termed  the  supe- 
rior, middle,  and  inferior  occipital.     They  are  often  not  well  marked.     In 


Tig.  332. — Lateral  view  of  the  brain  ^semi-diagrammatic) .  F,  Frontal  lobe;  P,  Parietal 
lobe;  0,  Occipital  lobe  ;  T,  Temporo-spbenoidal  lobe;  S,  fissure  of  Sylvius;  S.  hori- 
zontal, S",  ascending  ramus  of  the  same  ;  c,  sulcus  centralis  (fissure  of  Rolando)  ; 
A,  ascending  frontal  ;  B,  ascending  parietal  convolution  ;  Fi,  superior ;  F2,  middle  : 
F3,  inferior  frontal  convolutions  ;  fi,  superior,  f-2,  inferior  frontal  sulcus  ;  f3,  prte- 
central  sulcus  ;  Pi,  superior  parietal  lobule  ;  P2,  inferior  parietal  lobule  consisting  of 
P2,  supramarginal  gyrus,  and  P2',  angular  gyrus ;  ip,  interparietal  sulcus  ;  cm,  ter- 
mination of  calloso-marginal  fissure;  Oi,  first,  O2,  second,  O3,  third  occipital  convo- 
lutions ;  po,  parieto-oecipital  fissure ;  o,  transverse  occipital  fissure  ;  02,  sulcus 
occipitalis  inferior  ;  Ti,  first,  T2,  second,  T3,  third  temporo-sphenoidal  convolutions  ; 
ti,  first,  t2,  second  temporo-sphenoidal  fissures.     (Ecker.) 


man.  the  external  parieto-oecipital  fissure  is  only  to  be  distinguished  as  a 
notch  in  the  inner  edge  of  the  hemisphere  ;  below  this  it  is  quite  obliterated 
by  the  four  annectent  gyri  (pi  is  de  passage)  which  run  nearly  horizontally. 
The  upper  two  connect  the  parietal,  and  the  lower  two  the  temporal  with 
the  occipital  lobe. 

5.  The  central  lobe,  or  island  of  Keil,  which  contains  a  number  of  radiat- 
ing convolutions  (gyri  operti). 


•  bap.  xviir.]       <;vi;l    am»    BUL(  I    OF    CEREBRUM. 


603 


nternal  surface  (fig.  334)  contains  the  following  gyri  and  sulci : 
Gyrus  fornicatus,  a  long  curved   1 rotation,  parallel   to  and  curving 

round  the  corpus  callosum,  and  swelling  out  a1   its  hinder  and  upper  mmI 

into  the  quadrate  Lobule  (precuneus ),  which  is  continuous  with  ih<-  superior 

parietal  lobule  on  the  external  surface. 

Marginal  convolution  runs  parallel  to  the  preceding,  and  occupies  the 

space  between  it  and  the  edge  of  the  Longitudinal  fissure. 
The  two  convolutions  are  separated  by  the  calloso-margina]  fissi 
The  internal  perpendicular  fissure  iswell  marked,  and  runs  down  waj 

its  junction  with  the  caleaHne  fissure:  the  v.  aped  mass  intervening 


Tig.  333. — Vu  "■  of  the  brain  from  above  [semi-diagrammatic).     Si,  end  of  horizontal  ramus 
of  fissure  of  Sylvius.    The  other  letters  refer  to  the  same  parts  as  in  Fit,'.  352.     [Ecker.  1 


between  these  two  is  termed  the  euneus.  The  calcarine  fissure  corresponds 
to  the  projection  into  the  posterior  cornu  of  the  lateral  ventricle,  termed 
the  Hippocampus  minor.  The  temporosphenoidal  lobe  on  its  internal 
aspect  is  seen  to  end  in  a  hook  (uncinate  gyrus).  The  notch  round  winch 
it  curves  is  continued  up  and  back  as  the  dentate  or  hippocampal  sulcus  ; 
this  fissure  underlies  the  projection  of  the  hippocampus  major  within  the 
brain.  There  are  three  internal  temporo-occipital  convolutions,  of  which 
the  superior  and  inferior  ones  are  usually  well  marked,  the  middle  one 
generally  less  so. 


604 


THE  NERVOUS  SYSTEM, 


['  BAP.  XVlll. 


The  collateral  fissure  (corresponding  to  the  eminentia  collateralis)  forms 
the  lower  boundary  of  the  superior  temporo-occipital  convolution. 

All  the  above  details  will   be  found  indicated  in  the  diagrams  (figs.  332. 

OJJ>    JJ-r'- 


-  IJ 


Fig.  334. — View  of  the  right  hemisphere  in  the  median  -     .  ,;-dia<rrarnmati'-  .     CC.  cor- 

pus eallosum  longitudinally  divided  :  Gff,  syrus  fomicatus  :  H.  gyrus  hippocampi : 
h,  sulcus  hippocampi  :  U.  uncinate  gyrus  :  cm.  caUoso-marginal  fissure  ;  Fi,  median 
aspect  of  first  frontal  convolution  :  c,  terminal  portion  of  sulcus  centralis  'fissure  of 
Rolando  :  A,  amending  frontal :  B.  ascending  parietal  convolution;  Pi',  precuneus  : 
Oz,  cuneus  :  po,  parieto-oceipital  fissure ;  o.  sulcus  occipitalis  transversua  ;  oc.  calcarine 
fissure;  oc',  superior;  oc",  inferior  ramus  of  the  same:  1),  gyrus  descendens ;  T\i. 
gyrus  occipito-temporalis  lateralis  loLulus  fusiformis  :  T5,  gyrus  occipito-temporali- 
medialis   lobulus  lingualis  .     (Eeker. 


Structure. — The   cortical  grey  matter  of  the   brain  consists  of 
five  layers  (Meynert)  (fig.  335). 

1.  Superficial  layer  with  abundance  of  neuroglia  and  a  few 
small  multipolar  ganglion-cells.  2.  A  large  number  of  closely 
packed  small  ganglion-cells  of  pyramidal  shape.  3.  The  most 
important  layer,  and  the  thickest  of  all  :  it  contains  many  1 
pyramidal  ganglion-cells,  each  with  a  process  running  off  from 
the  apex  vertically  towards  the  free  surface,  and  lateral  pro- 
cesses at  the  base  which  are  always  branched.  Also  a  median 
process  from  the  base  of  each  cell  which  is  unbranched  and 
becomes  continuous  with  the  axis-cylinder  of  a  nerve-fibre.  4. 
Numerous  ganglion-cells:  termed  the  "granular  formation"  by 
.Meynert.  5.  Spindle-shaped  and  branched  ganglion-cells 
moderate-size  arranged  chiefly  parallel  to  the  free   surface  (vide 

fi?-  335)- 


I  II  \V.   X\  III. 


TilK   CEREBRAL   COM  EX. 


605 


According  to  recenl  observations 
centra  become  connected  with  the 


*\ 


? 


by  B  the  fibres  of  the  medullary 

multipolar  ganglion  ••'■lis  of  the  fourth 
layer,  and,  from    thi 
Latter,  branches  pass  to 
the  angles  at  the  bases      ,:  • 
of  the   pyramidal   cells 
of  the  third  Layer  of  the 
cortex  (fig.  $57.  a).  From 
the  apices  of  the  pyra- 
midal   cells,    the    axis- 
cylinder  processes  pass 
upwards  for  a  consider-      »j 
able  distance,  and  finally 
terminate  m  ovoid  cor-       9 
puscles  (fig.  336)  closely       | 
resembling,  and  homolo- 
gous with,  the  corpuscles       ! 
in    which   the   ultimate 
ramifications      of      the 
branched   cells  of    Pur- 
kinje  in  the  cerebellum 
terminate.         Thus      it 
would    seem    that    the 
large  pyramidal  cells  of 
the  third  layer  are  them-        9 
-elves  homologous  with 
the  cells  of  Purkinje  in       -''v 

the  cerebellum. 

Fig--  336. 


Fig.  335. —  The  layers  of  the  cortical  grey 
matter  of  the  cerebrum.      Meynert.) 


Kg.  337. — ^Drawn  by  GK  Munro  Smith 
from  ammonium  bichromate  prepa- 
rations by  E.  C.  Bousfield.l 


The  white  matter  of  the  brain,  us  of  the  spinal  cord,  consists  of 
bundles  of  medullated,  and,  in  the  neighbourhood  of  the  grey 
matter,    of  non-medullated    nerve-fibre-,    which,    however,    as    is 


6o6 


THE  NERVOUS  SYSTEM. 


[chap.  XVIII. 


the  case  in  the  central  nervous  system  generally,  have  mo  ex- 
ternal  nucleated  nerve-sheath,  which  are  held  together  by  deli- 
cate connective    tissue.      The  size  of  the  fibres   of  the  brain  is 

usually  less  than  that  of  the  fibres  of  the 
spinal  cord  :  the  average  diameter  of  the 


fes 


former  being  about 


of  an  inch. 


1  0,000 

Chemical  Composition. —  The  che- 
mistry of  nerve  and  nerve  cells  has  been 
chiefly  studied  in  the  brain  and  spinal 
cord.  Nerve  matter  contains  several  albu- 
minous and  fatty  bodies  (cerebrin,  lecithin, 
and  some  others),  also  fatty  matter  which 
can  be  extracted  by  ether  (including  choles- 
terin)  and  various  salts,  especially  Potas- 
sium and  Magnesium  phosphates,  which 
exist  in  larger  quantity  than  those  of 
Sodium  and  Calcium.  Yolk  of  egg  resem- 
bles cerebral  substance  very  closely  in  its 
chemical  composition  ;  milk  and  muscle 
also  come  very  near  it. 

The  great  relative  and  absolute  size  of  the 
Cerebral  hemispheres  in  the  adult  man.  masks 
to  a  great  extent  the  real  arrangement  of  the 
several  parts  of  the  brain,  which  is  illustrated  in 
the  two  accompanying  diagrams. 

From  these  it  is  apparent  that  the  parts  of  the 
brain  are  disposed  in  a  linear  series,  as  follows 
(from  before  backwards)  :  olfactory  lobes,  cere- 
bral hemi.-pheres,  optic  thalami.  and  third  ven- 
tricle, corpora  quadrigemina.  or  optic  lobes. 
cerebellum,  medulla  oblongata. 

This   linear   arrangement    of    parts    actually 
occurs  in  the  human  foetus  (see  Chapter  on  De- 
velopment), and  it  is  permanent  in  some  of  the 
lower  A'ertebrata,  e.g.}  Fishes,  in  which  the  cere- 
bral hemispheres  are   represented  by  a  pair  of 
ganglia  intervening  between  the  olfactory  and 
the  optic  lobes,  and  considerably  smaller  than 
the  latter.     In  Amphibia  the  cerebral  lobes  are 
further  developed,  and  are  larger  than  any  of 
the  other  ganglia. 
In  Eeptiles  and  Birds  the  cerebral  ganglia  attain  a  still  further  develop- 
ment, and  in  Mammalia  the  cerebral  hemispheres  exceed  in  weight  all  the 
rest  of  the  brain.     As  we  ascend  the  scale,  the  relative  size  of  the  cerebrum 
increases,  till  in  the  higher  apes   and  man  the  hemispheres,  which  com- 


ing. 338. — Diagrammatic  hori- 
zontal section  of  a  Vertebrate 
brain.  The  figures  serve  loth 
for  this  and  the  next  diagram. 

Mb,  mid  brain  :  what  lies  in 
front  of  this  is  the  fore-, 
and  what  lies  behind,  the 
hind-brain ;  L  Uaruina  termi- 
nalis  ;  Olf,  olfactory  lobe-  : 
Hmp,  hemispheres ;  Th.  E, 
thalamencephalon  ;  Pa.  pi- 
neal gland :  Py,  pituitary 
body ;  F.  J/,  foramen  of 
Itfunro  :  es,  corpus  striatum ; 
Th,  optic  thalamus:  CC, 
crura  cerebri :  the  mass  lying 
above  the  canal  represents 
the  corpora  quadrigeinina  ; 
Ch,  cerebellum;  I— IX., the 
niue  pairs  of  cranial  nerves  ; 
1, 'olfactory  ventricle;  2,  late- 
ral ventricle ;  3,  third  ven- 
tricle ;  4,  fourth  ventricle ; 
— .  iter  a  tertio  ad  quartuni 
ventriculum.     (Huxley.) 


(  HAP.   Will.] 


WEIGHT   OF  THE   BRAIN. 


607 


menoed  as  two  little  lateral  bud  .  the  [ante]  have 

1    apwarda  and   I  :-.  compl 

view  all  tl  brain.    Attheaame  time  th< 

brain,  in  many  lower  Mammalii  .  -  the  rabbit,  is  replaced  by  the  laby- 

rinth of  convolir  aman  brain. 

II  -  ght  of  tin    Brain. — The  brain  of  an  adult  man  w  -         t 

— or  about  3  I  r  animals 

except  the  elephant  and  whale.     It- we:.  Hvely  to  that  of  the 

is  only  exceeded  by  that  of  a  fewamall   birda  and   -  smaller 

monkeys.     In  the  adult  man  it  m     —       Et]  jght. 


19. — Longii  Letters  as 

before.    Lamina  teiniinalis  is  represented  by  the  strong  black  line  joinin?  1 
[Huxley. 


Variations.  Age. — In  a  new-born  child  the  brain  (weighing  10 — 14  <-z.) 
is  ^j  of  the  I'  Jit.     At  the  age  of  7  years  the  v.    ighl        the  brain 

already  averages  40  oz..  and  about  14  years  the  brain  not  unfrequently 
reaches  the  weight  of  48  oz.     Beyond  the  age  of  40  years  the  slowly 

but  steadily  declines  at  the  rate  of  about  1  oz.  in  10  year-. 

s  . — The  average  weight  of  the  female  brain  is  less  than  the  male  :  and 
this  difference  persists  E  m  birth  throughout  life.  In  the  adult  it  amounts 
to  about  5  oz.     Thus  the  average  weight  of  an  adult  woman's  brain  is  about 

44  "7- 

Intelligence. — The  brains  of  idiots  are  generally  much  below  the  av. 
some  weighing  less  than  16  oz.     Still  the  facts  at  present  collec: 
warrant  more  than  a  very  general  statement,  to  which  there  are  numerous 
exceptions,  that  the  brain  weight   corresponds  to   some   extent  wit: 
degree  of  intelligence.     There  can  be  little  doubt  that  the  complexity  and 

of  the  convolutions,  which  indicate  the  area  of  the  grey  matter 
cortex,  correspond  with  the  degree  of  intelligence  (II.  Wagner). 

H         -  S  I     •d. — The  spinal  cord  of  man  w  1  —  r 

ight  relatively  to  the  brain  is  about  1  :  ^6.  A-  we  descend  the 
scale,  this  ratio  constantly  increases  till  in  the  mous  •  i t  is  1  :  \.  In  cold- 
blooded animals  the  relation  is  reversed,  the  spinal  cord  is  the  heavier 
and  the  more  important  organ.      In  the  newt,  2:1:   and  in  the  lamprey. 

75  :i- 

Characters  of the  Jin  man  J!  rain. — The  following  character 
--uish  tlu    brain   of  man  and  apes  from   tl  all  other  animals. 

.  The  rudimentary  condition  of  the  olfactory  lobes,     (b).  A  perfectly  de- 
fined fissure  of  Sylvius.     (<?).  A  |  — :erior  lobe  completely  covering  the  cere- 


6o8 


THE  NERVOUS  SYSTEM. 


[CHAP.  XVIII, 


bellum.     (77).  The  presence  of  posterior   cornna   in  the  lateral  ventricles 
(Gratiolet). 
The  most  distinctive  points  in  the  human  brain,  as  contrasted  with  that 

of  apes,  are:— (i).  The  much  greater  size  and  weight  of  the  whole  brain. 
The  brain  of  a  full-grown  gorilla  weighs  only  about  15  oz.,  which  is  less  than 
I  the  weight  of  the  human  adult  male  brain,  and  barely  exceeds  that  of  the 
human  infant  at  birth.  (2).  The  much  greater  complexity  of  the  convolu- 
tions, especially  the  existence  in  the  human  brain  of  tertiary  convolution-  in 
the  sides  of  the  fissures.     (3).  The  greater  relative  size  and  complexity,  and 


Fi".  340. — Brain  of  the  Orang,  f  natural  size,  showing  the  arrangement  of  the  convolutions. 
By  fissure  of  Sylvius;  i?,  fissure  of  Eolando  :  EP,  external  perpendicular  fissure; 
Olf,  olf actory  lobe ;  ' 'A.  cerebellum ;  PV,  pons  Varolii ;  31 0,  medulla  oblongata .  As 
contrasted  with  the  human  brain,  the  frontal  lobe  is  short  and  small  relatively,  the 
fissure  of  Sylvius  is  oblique,  the  temporo-sphenoidal  lobe  very  prominent,  and  the  ex 
temal  perpendicular  fissure  very  well  marked.      Gratiolet.) 

the  blunted  quadrangular  contour  of  the  frontal  lobes  in  man.  which  are 
relatively  both  broader,  longer,  and  higher,  than  in  apes.  In  apes  the 
frontal  lobes  project  keel-like  (rostrum)  between  the  olfactory  bulbs. 
(4).  The  much  greater  prominence  of  the  temporo-sphenoidal  lobe  in  apes. 
(5).  The  fissure  of  Sylvius  is  nearly  horizontal  in  man.  while  in  apes  it 
slants  considerably  upwards.  (6).  The  distinctness  of  the  external  perpen- 
dicular fissure,  which  in  apes  is  a  well-defined  almost  vertical  "slash,"  while 
in  man  it  is  almost  obscured  by  the  annectent  gyri  (Rolleston). 

Most  of  the  above  points  are  shown  in  the  accompanying  figure  of  the 
brain  of  the  Oralis-. 


Functions.- — (1.)  The  Cerebral  hemispheres  are  the  organs  by 
which  are  perceived  those  clear  and  more  impressive  sensations 
which  can  be  retained,  and  regarding  which  we  can  judge.     (2.) 


chap,  mil.]        1T.\<  Tinvs   OF  THE  CEBEBRUM.  6o> 

The  Cerebrum  la  the  organ  of  the  will,  in  bo  far  at  leu  acfa 

act  of  the  will  requires  a  deliberate,  however  quick  determination* 
(3.)  It  is  the  means  of  retaining  impressions  of  sensible  thn 
and  reproducing  them  in  subjective  sensations  and  ideas.  '4.)  It 
is  the  medium  of  all  the  higher  emotions  and  feelings,  and  of  the 
faculties  of  judgment,  understanding,  memory,  reflection,  induction, 
imagination  and  the  like. 

Evidence  regarding  the  physiology  of  the  cerebral  hemispb 
has  been  obtained,  as  in  the  f  other  parts  of  the  uervi 

system,  from  the  study  of  Comparative  Anatomy,  from  Pathology^ 
and  from  Experiments  on  the  lower  animals.     The  chief  eviden 

!garding  the  functions  of  the  Cerebral  hemispheres  derived  from 
these  various  sources,  are  briefly  these  : — 1.  Any  severe  injury 
of  them,  such  as  a  general  concussion,  or  sudden  pressure  by 
apoplexy,  may  instantly  deprive  a  man  of  all  power  of  manifesting 
externally  any  mental  faculty.  2.  In  the  same  general  proportion 
the  higher  mental  faculties  are  developed  in  the  Vertebrate 
animals,  and  in  man  at  different  ages  and  in  different  individuals, 
the  more  is  the  size  of  the  cerebral  hemispheres  developed  in  com- 
parison with  the  rest  of  the  cerebro-spinal  system.  3.  No  other 
part  of  the  nervous  system  bears  a  corresponding  proportion  to 
the  development  of  the  mental  faculties.  4.  Congenital  and  other 
morbid  defects  of  the  cerebral  hemisphere  are,  in  general,  accom- 
panied by  corresponding  deficiency  in  the  range  or  power  of  the 
intellectual  faculties  and  the  higher  instincts.  5.  Removal  of  the 
cerebral  hemispheres  in  one  of  the  lower  animals  produces  effects 
corresponding  with  what  might  be  anticipated  from  the  foregoing 
facts.  The  animal,  although  retaining  mere  sensation,  and  the 
power  of  performing  even  complicated  reflex  acts,  remains  in  ;* 
state  of  stupor,  and  performs  no  voluntary  movement  of  any  kind. 
(See  below.) 

Effects  of  the  Removal  of  the  Cerebrum. — The  removal 
of  the  cerebrum  in  the  lower  animals  appears  t"  reduce  them. 
to  the  condition  of  a  mechanism  without  spontaneity.  A  pigeon 
from  which  the  cerebrum  has   been  removed  will   remain  motion- 

3    and    apparently    unconscious  unless   disturbed.     When    d 
turbed    in    any  way  it   soon    recovers   its  former  position;    when 
brown  into  the  air  it  flies. 

In  the  case   of  the  frog,  when  the   cerebral  lobes    have    been 

p.  E. 


6lO  THE  NERVOUS   SYSTEM.  [chap,  win. 

removed,  the  animal  appears  similarly  deprived  of  all  power  of 
spontaneous  movement.  But  it  sits  up  in  a  natural  attitude, 
breathing  quietly  ;  when  pricked  it  jumps  away;  when  thrown 
into  the  water  it  swims ;  when  placed  upon  the  palm  of  the 
hand  it  remains  motionless,  although,  if  the  hand  be  gradually 
tilted  over  till  the, frog  is  on  the  point  of  losing  his  balance,  he 
will  crawl  up  till  lie  regains  his  equilibrium,  and  comes  to  be 
perched  quite  on  the  edge  of  the  hand.  This  condition  contrasts 
with  that  resulting  from  the  removal  of  the  entire  brain,  leaving 
only  the  spinal  cord ;  in  this  case  only  the  simpler  reflex  actions 
can  take  place.  The  frog  does  not  breathe,  he  lies  flat  on  the 
table  instead  of  sitting  up  ;  when  thrown  into  a  vessel  of  water  he 
sinks  to  the  bottom ;  when  his  legs  are  pinched  he  kicks  out,  but 
does  not  leap  away. 

Unilateral  action. — Respecting  the  mode  in  which  the  brain 
discharges  its  functions,  there  is  no  evidence  whatever.  But  it 
appears  that,  for  all  but  its  highest  intellectual  acts,  one  of  the 
cerebral  hemispheres  is  sufficient.  For  numerous  cases  are 
recorded  in  which  no  mental  defect  was  observed,  although  one 
cerebral  hemisphere  was  so  disorganised  or  atrophied  that  it  could 
not  be  supposed  capable  of  discharging  its  functions.  The  remain- 
ing hemisphere  was,  in  these  cases,  adequate  to  the  functions 
generally  discharged  by  both  ;  but  the  mind  does  not  seem  in  any 
of  these  cases  to  have  been  tested  in  very  high  intellectual  exer- 
cises ;  so  that  it  is  not  certain  that  one  hemisphere  will  suffice  for 
these.  In  general,  the  mind  combines,"  as  one  sensation,  the  im- 
pressions which  it  derives  from  one  object  through  both  hemispheres, 
and  the  ideas  to  which  the  two  such  impressions  give  rise  are 
single.  In  relation  to  common  sensation  and  the  effort  of  the 
will,  the  impressions  to  and  from  the  hemispheres  of  the  brain  are 
carried  across  the  middle  line  ;  so  that  in  destruction  or  com- 
pression of  either  hemisphere,  whatever  effects  are  produced  in 
loss  of  sensation  or  voluntary  motion,  are  observed  on  the  side  of 
he  body  opposite  to  that  on  which  the  brain  is  injured. 

Localisation  of  functions. — In  speaking  of  the  cerebral 
hemispheres  as  the  so-called  organs  of  the  mind,  they  have  been 
regarded  as  if  they  were  single  organs,  of  which  all  parts  are 
equally  appropriate  for  the  exercise  of  each  of  the  mental  faculties. 
But  it  is  possible  that  each  faculty  has   a  special  portion  of  the 


char  xviii.]         FUNCTIONS  OF  THE  CEREBRUM.  f,ii 

brain  appropriated  to  it  as  its  proper  organ.  For  this  theory  the 
principal  evidences  are  as  follows: — i.  That  it  is  in  accordance 
with  the  physiology  of  the  compound  organs  or  systems  in  the 
body,  in  which  each  part  lias  its  special  function  ;  as,  for  example] 
<>t'  the  digestive  Bystem,  in  which  the  stomach,  liver,  and  other 
organs  perform  each  their  separate  share  in  the  general  process  of 
the  digestion  of  the  food.  2.  That  in  different  individuals  the 
ral  mental  functions  are  manifested  in  very  different  degrees. 
Even  in  early  childhood,  before  education  can  be  imagined  to 
have  exercised  any  influence  on  the  mind,  children  exhibit  various 
dispositions — each  presents  some  predominant  propensity,  or 
evinces  a  singular  aptness  in  some  study  or  pursuit ;  and  it  is  a 
matter  of  daily  observation  that  every  one  has  his  peculiar  talent 
<>v  propensity.  But  it  is  difficult  to  imagine  how  this  could  be 
the  case,  if  the  manifestation  of  each  faculty  depended  on  the 
whole  of  the  brain;  different  conditions  of  the  whole  mass  might 
affect  the  mind  generally,  depressing  or  exalting  all  its  functions 
in  an  equal  degree,  but  could  not  permit  one  faculty  to  be  strongly 
and  another  weakly  manifested.  3.  The  plurality  of  organs  in 
the  brain  is  supported  by  the  phenomena  of  some  forms  of  mental 
derangement.  It  is  not  usual  for  all  the  mental  faculties  in  an 
insane  person  to  be  equally  disordered;  it  often  happens  that  the 
strength  of  some  is  increased,  while  that  of  others  is  diminished; 
and  in  many  cases  one  function  only  of  the  brain  is  deranged,. 
while  all  the  rest  arc  performed  in  a  natural  manner.  4.  The 
same  opinion;  is  supported  by  the  fact  that  the  several  mental 
faculties  are  developed  to  their  greatest  strength  at  different 
periods  of  life,  some  being  exercised  with  great  energy  in  child- 
hood, others  only  in  adult  age ;  and  that,  as  their  energy  decreases 
in  old  age,  there  is  not  a  gradual  and  equal  diminution  of  power 
in  all  of  them  at  once,  but,  on  the  contrary,  a  diminution  in  one 
Or  more,  while  others  retain  their  full  strength,  or  even  increase 
in  power.  5.  The  plurality  of  cerebral  organs  appears  to  be  indi- 
cated by  the  phenomena  of  dreams,  in  which  only  a  part  of  the 
mental  faculties  are  at  rest  or  asleep,  while  the  others  are  awake, 
and,  it  is  presumed,  are  exercised  through  the  medium  of  the  parts 
of  the  brain  appropriated  to  them. 

Unconscious  Cerebration. — In  connection  with  the  above, 
some   remarkable   phenomena  should  be  mentioned  which   hav. 

it  it  2 


6l2  THE  NERVOUS   SYSTEM.  [chap.  xvm. 

been  described  as  depending  on  an  unconscious  action  of  the 
brain. 

It  must  be  within  the  experience  of  every  one  to  have  tried 
to  recollect  some  particular  name  or  occurrence  :  and  after  trying 
in  vain  for  some  time  the  attempt  is  given  np  and  qnite  for- 
gotten amid  other  occupations,  when  suddenly,  hours  or  even  a 
day  or  two  afterwards,  the  desired  name  or  occurrence  unex- 
pectedly flashes  across  the  mind.  Such  occurrences  are  supposed 
by  many  to  be  due  to  the  requisite  cerebral  processes  going  on 
unconsciously,  and,  when  the  result  is  reached,  to  our  all  at  once 
becoming  conscious  of  it. 

That  unconscious  cerebration  may  sometimes  occur,  is  likely 
enough;  and  it  is  paralleled  by  the  unconscious  walking  of  a 
somnambulist.  But  many  cases  of  so-called  unconscious  cerebra- 
tion are  better  explained  by  the  supposition  that  some  missing- 
link  in  the  chain  of  reasoning  cannot  at  the  moment  be  found  ; 
but  is  afterwards,  by  some  chance  combination  of  events,  sug- 
gested, and  thus  the  mental  process  is  at  once,  with  the  memory 
of  what  has  gone  before,  completed. 

Again,  in  the  vain  endeavour  to  solve  a  difficult  or  it  may  be  an 
easy  problem,  the  reasoner  is  frequently  in  the  condition  of  a 
man  whose  wearied  muscles  could  never,  before  they  have  rested, 
overcome  some  obstacles.  In  both  cases, — of  brain  and  muscle, 
after  renewal  of  their  textures  by  rest,  the  task  is  performed  so- 
rapidly  as  to  seem  instantaneous. 

Aphasia. — From  the  apparently  greater  frequency  of  inter- 
ference with  the  faculty  of  speech  in  disease  of  the  left  than  of  the 
right  half  of  the  cerebrum,  it  has  been  thought  that  the  nerve- 
centre  for  language,  including  in  this  term  all  articulate  expression 
of  ideas,  is  situated  in  the  left  cerebral  hemisphere.  A  large 
number  of  cases  are  on  record  in  which  aphasia,  or  the  loss  of 
power  of  expressing  ideas  in  words,  has  been  associated  with 
disease  of  the  posterior  part  of  the  lower  or  third  frontal  convolu- 
tion on  the  left  side.  This  condition  is  usually  associated  with 
paralysis  of  the  right  side  (right  hemiplegia).  The  only  conclu- 
sion, however,  which  can  be  drawn  from  this,  is,  that  the  integrity 
of  this  particular  convolution  is  essential  to  the  faculty  of  speech  ; 
we  cannot  conclude  that  it  is  necessarily  the  centre  for  language. 
It  may  be  only  one  link  in  the  complete  chain  of  nervous  con- 


chap,  .win.]        FUNCTIONS  OF  THE  CEBEBRUM,  Q{^ 

nections  necessary  for  the  translation  of  an  idea  into  articulate 
expression. 

It  seems  highly  probable  that  the  corresponding  right  convo- 
lutions can  take  on  the  same  functions  as  the  left ;  and  it  is  in  this 
way  that  we  can  explain  those  cases  in  which  recovery  of  speech 
takes    place,    though    the    left   frontal    convolution    still     remains 

diseased. 

Pineal  and  Pituitary  Bodies. 

Nothing  is  known  of  the  function  of  the  pineal  and  pituitary 
bodies.  They  have  been,  indeed,  supposed  by  some  to  be  rather 
ductless  glands  than  nervous  organs  (p.  472). 

Experimental  localisations. — Attempts  have  been  made  to 
localise  cerebral  functions  by  means  of  experiments  on  the  lower 
animals.  It  had  long  been  well  known  that  the  cerebral  hemi- 
spheres could  not  be  excited  by  mechanical,  chemical,  or  thermal 
stimuli,  but  Fritsch  and  Hitzigwere  the  first  to  show  that  they  are 
amenable  to  electric  irritation.  The}-  employed  a  weak  constant 
current  in  their  experiments,  applying  a  pair  of  fine  electrodes  not 
more  than  ^.,  in.  apart  to  different  parts  of  the  cerebral  cortex.  The 
results  thus  obtained  have  been  confirmed  and  extended  by  Ferrier. 

The  following  are  the  fundamental  phenomena  observed  in  all 
these  cases : 

(1.)  Excitation  of  the  same  spot  is  always  followed  by  the  same 
movement  in  the  same  animal.  (2.)  The  area  of  excitability  for 
any  given  movement  is  extremely  small,  and  admits  of  very  accu- 
rate definition.  (3.)  In  different  animals  excitations  of  anatomically 
corresponding  spots  produce  similar  or  corresponding  results 
(Burdon-Sanderson). 

The  various  definite  movements  resulting  from  the  electric 
stimulation  of  circumscribed  areas  of  the  cerebral  cortex,  are 
enumerated  in  the  description  of  the  accompanying  figures  of  the 
dog  and  monkey's  brain. 

In  the  case  of  the  dog,  the  results  obtained  are  summed  up  as 
follows,  by  Hitzig. 

('(.)  One  portion  (anterior)  of  the  convexity  of  the  cerebrum  is 
motor;  another  portion  (posterior)  is  11011  motor.  (6.)  Electric 
stimulation  of  the  motor  portion  produces  co-ordinated  muscular 
contraction  on  the  opposite  side  of   the  body.       (c.)  With  very 


614 


THE   XEKVOUS   SYSTEM. 


[chap.  XVI II. 


weak  currents,  the  contractions  produced  are  distinctly  limited  to 
particular  groups  of  muscles  ;  with  stronger  currents  the  stimulus 
is  communicated  to   other  muscles  of  the  same   or  neighbouring 

} tarts.  (d.)  The  portions 
of  the  brain  intervening 
between  these  motor  centres 
are  inexcitable  by  similar 
means. 

With  regard  to  the  facts 
above  mentioned,  all  ex- 
perimenters are  agreed,  but 
there  is  still  considerable 
diversity  of  opinion  as  to 
their  explanation. 

It  is  evident  that  the 
spots  marked  out  on  the 
cortex  are  not  strictly 
speaking  motor  centres,  for 
they  can  be  removed  en- 
tirely without  destroying 
the  power  of  voluntary 
motion. 

Burdon  -  Sanderson  has 
shown  that  electric  stimu- 


Figs.  341  and  342.  —  B>  -a  hi  of  dog,  viewed  from  above  and  in  profile.  F,  frontal  fissure,  sometimes- 
termed  crucial  sulcus,  corresponding  to  the  fissure  of  Rolando  in  man ;  S,  fissure  of 
Sylvius,  around  which  the  four  longitudinal  convolutions  are  concentrically  arranged  ; 
1.  flexion  of  head  on  the  neck,  in  the  median  line  ;  2,  flexion  of  head  on  the  neck, 
with  rotation  towards  the  side  of  the  stimulus  ;  3,  4,  flexion  and  extension  of  anterior 
limb  ;  5,  6,  flexion  and  extension  of  posterior  limb  ;  7,  8,  9,  contraction  of  orbicularis 
oculi,  and  the  facial  muscles  in  general.  The  unshaded  part  is  that  exposed  by  open- 
ing the  skull.     (Dalton.) 


chap.  win. 


FUNCTIONS   OF  THE   CEREBRUM. 


615 


lation  of  different  points  in  ;i  horizontal  section,  through  the 
deeper  porta  <>t'  the  hemispheres,  produces  the-  same  effects  as 
stimulation  of  the 
so-called  "centres" 
in  the  grey  matter 
overlying  them  : 
while  the  same 
results  follow  elec- 
tric stimulation  of 
different  points  of 
the  corpus  stria- 
tum.      * 

In  applying  the 
facts      ascertained 
by    these     experi- 
ments    to     elucidate     the 
physiology    of   the    human 
brain,   we   must   remember 
that  the  method  of  electric 
stimulation  is  an   artificial 
one,   differing   widely  from 
the     ordinary    stimuli     to 
which  the  brain  is  subject 
during  life. 

Functions  of  Other 
parts  of  the  Brain. — Of 

the  physiology  of  the  other 
parts  of  the  brain,  little  or 
nothing  can  be  said. 

Of  the  offices  of  the 
corpus  cal/osinn,  or  great 
transverse       and       oblique 

Fie1.  3  «• 

Figs.  343  and  344. — Diagrams  of  monkey's  brain  to  show  the  effects  of  electric  stimulation  ttf 
certain  spots.  1,  movement  of  hind  foot;  2,  chiefly  adduction  of  foot;  3,  movements 
of  hind  foot  and  tail;  4,  of  latissimus  dorsi ;  5,  extension  forward  of  arm;  a,  b,  c,d, 
movements  of  hand  and  wrist ;  6,  supination  and  flexion  of  forearm  ;  7,  elevation  of 
upper  lip ;  8,  conjoint  action  of  elevation  of  upper  lip  and  depression  of  lower ;  9,  opening; 
of  mouth  and  protrusion  of  tongue  ;  10,  retraction  of  tongue  ;  11,  action  of  platysma  ; 
12 ,  elevation  of  eyebrows  and  eyelids,  dilatation  of  pupils,  and  turning  head  to  opposite 
side;  13,  eyes  directed  to  opposite  side  and  upwards,  with  usually  contraction  of  the 
pupils  ;  13',  similar  action,  but  eyes  usually  directed  downwards  ;  14,  retraction  of  op- 
posite ear,  head  turns  to  the  opposite  side,  the  eyes  widely  opened  and  pupils  dilated; 
15,  stimulation  of  this  region,  which  corresponds  to  the  tip  of  the  uncinate  convolu- 
tion, causes  torsion  of  the  lip  and  nostril  of  the  same  side.     (Ferrier.) 


6i6 


THE  NERVOUS   SYSTEM. 


[chap.  XVIII." 


commissure  of  the  brain,  nothing  positive  is  known.  But 
instances  in  which  it  was  absent,  or  very  deficient,  either  without 
any  evident  mental  defect,  or  with  only  such  as  might  be  ascribed 
to  coincident  affections  of  other  parts,   make  it  probable  that  the 


Tig.  345. — View  of  the  corpus  cdUosum  from  above.  \. — The  upper  surface  of  the  corpus 
eallosum  has  been  fully  exposed  by  separating-  the  cerebral  hemispheres  and  throwing 
them  to  the  side  ;  the  gyrus  fornicatus  has  been  detached,  and  the  transverse  fibres  of 
the  corpus  eallosum  traced  for  some  distance  into  the  cerebral  medullary  substance. 
1,  the  upper  surface  of  the  corpus  eallosum  ;  2,  median  fmrow  or  raphe  ;  5,  longitu- 
dinal strite  bounding  the  furrow  ;  4,  swelling  formed  by  the  transverse  bands  as  they 
pass  into  the  cerebrum;  5,  anterior  extremity  or  knee  of  the  corpus  eallosum;  t>, 
posterior  extremity ;  7,  anterior,  and  8,  posterior  part  of  the  mass  of  fibres  proceed- 
ing from  the  corpus  eallosum  ;  9.  margin  of  the  swelling  ;  10,  anterior  part  of  the 
convolution  of  the  corpus  eallosum ;  11.  hem  or  band  of  union  of  this  convolution  ; 
12,  internal  convolutions  of  the  parietal  lobe  ;  15,  upper  surface  of  the  cerebellum. 
(Sappey  after  Foville.) 


office  which  is  commonly  assigned  to  it,  of  enabling  the  two  sides 
of  the  brain  to  act  in  concord,  is  exercised  only  in  the  highest  acts 
of  which  the  mind  is  capable.  And  this  view  i.s  confirmed  by  the 
very  late  period  of  its  development,  and  by  its  very  rudimentary 
condition  (Flower)  in  all  but  the  placental  Mammalia. 

To  the  fornix  and  other  commissures  no  special  function  can  be 


CHAP.  XVIII. 


BLEEP.  Qij 


_nc<l ;  but  it  is  a  reasonable  hypotheau  that  they  conned  the 
action  of  the  parts  between  which  they  arc  severally  plai 

Sleep. 

All  parts  of   the  body   which   arc    the  scat  of   active  change 

require  periods  of  rest.     The  alternation  of  work  and   rest  is  a 

y  condition    of  their    maintenance  and   of  the   healthy 

performance  of  their  functions.     These  alternating  periods,  how- 
ever,  differ    much    in  duration  in  different  cases:    but,  for  any 

individual  instance,  they  preserve  a  general  and  rather  close 
uniformity.  Thus,  as  before  mentioned,  the  periods  of  rest  and 
work,  in  the  case  of  the  heart,  occupy,  each  of  them,  about  half  a 
..d  :  in  the  case  of  the  ordinary  respiratory  muscles  the  periods 
are  about  four  or  five  times  as  long.  In  many  cases,  again  |  -  : 
the  voluntary  muscles  during  violent  exercise)  while  the  periods 
during  active  exertion  alternate  very  frequently,  yet  the  expendi- 
ture goes  for  ahead  of  the  repair,  and.  to  compensate  for  thit 
after  repose  of  some  hours  becomes  necessary  ;  the  rhythm  being 
erfect  as  to  time,  than  in  the  case  of  the  muscles  concerned 
in  circulation  and  respiration. 

1  I  viously,  it  would  be  impossible  that,  in  the  case  of  the  Brain, 
there  should  be  short  periods  of  activity  and  repose,  or  in  other 
words,  of  consciousness  and  unconsciousness.  The  repose  must 
occur  at  long  intervals :  ami  it  must  therefore  be  proportionately 
long.  Hence  the  necessity  for  that  condition  which  we  call  Slttp  ; 
a  condition  which  seeming  at  first  sight  exceptional,  is  oiilv  an 
unusually  perfect  example  of  what  occurs,  at  varying  intervals,  in 
every  actively  working  portion  of  our  bodies. 

A  temporary  abrogation  of  the  functions  of  the  cerebrum 
imitating  sleep,  may  occur,  in  the  case  of  injury  or  die  a  -  the 
consequence  of  two  apparently  widely  different  conditions.  In- 
sensibility is  equally  produced  by  a  deficient  and  an  excx 
quantity  of  blood  within  the  cranium,  (coma)  :  but  it  was  once 
supposed  that  the  latter  offered  the  truest  analogy  to  the 
normal  condition  of  the  brain  in  sleep,  and  in  the  absence  of  any 
proof  to  the  contrary,  the  brain  was  said  to  be  during  sleep 
gested.  Direct  experimental  enquiry  has  led,  however,  to  the 
opposite  conclusion. 


6l8  THE  NEEWTOUS   SYSTEM.  [chap,  xviii. 

By  exposing,  at  a  circumscribed  spot,  the  surface  of  the  brain  of 
living  animals,  and  protecting  the  exposed  part  by  a  watch-glass, 
Durham  was  able  to  prove  that  the  brain  .becomes  visibly  paler 

(anaemic)  during  sleep  ;  and  the  anaemia  of  the  optic  disc  during 
sleep,  observed  by  Hnghlings  Jackson,  may  be  taken  as  a  strong 
confirmation,  by  analogy,  of  the  same  fact. 

A  very  little  consideration  will  show  that  these  experimental 
results  correspond  exactly  with  what  might  have  been  foretold 
from  the  analogy  of  other  physiological  conditions.  Blood  is 
supplied  to  the  brain  for  two  partly  distinct  purposes,  (i.)  It  is 
supplied  for  mere  nutrition's  sake.  (2.)  It  is  necessary  for  bring- 
ing supplies  of  potential  or  active  energy,  (i.e.,  combustible  matter 
or  heat)  which  may  be  transformed  by  the  cerebral  corpuscles  into 
the  various  manifestations  of  nerve-force.  During  sleep,  blood  is 
requisite  for  only  the  first  of  these  purposes ;  and  its  supply  in 
greater  quantity  would  be  not  only  useless,  but,  by  supplying  an 
excitement  to  work,  when  rest  is  needed,  would  be  positively 
harmful.  In  this  respect  the  varying  circulation  of  blood  in  the 
brain  exactly  resembles  that  which  occurs  in  all  other  energy 
transforming  parts  of  the  body;  e.g.,  glands  or  muscles. 

At  the  same  time,  it  is  necessary  to  remember  that  the  normal 
anaemia  of  the  brain  which  accompanies  sleep  is  probably  a  result 
and  not  a  cause  of  the  quiescence  of  the  cerebral  functions.  What 
the  immediate  cause  of  this  periodical  partial  abrogation  of  function 
is,  however,  we  do  not  know. 

Somnambulism  and  Dreams. — What  we  term  sleep  occurs 
often  in  very  different  degrees  in  different  parts  of  the  nervous 
system ;  and  in  some  parts  the  expression  cannot  be  used  in  the 
ordinary  sense. 

The  phenomena  of  dreams  and  somnambulism  are  examples  of 
differing  degrees  of  sleep  in  different  parts  of  the  cerebro-spinal 
nervous  system.  In  the  former  case  the  cerebrum  is  still  partially 
active;  but  the  mind-products  of  its  action  are  no  longer  corrected 
by  the  reception,  on  the  part  of  the  sleeping  sensorium,  of  impres- 
sions of  objects  belonging  to  the  outer  world  ;  neither  can  the 
cerebrum,  in  this  half-awake  condition,  act  on  the  centres  of  reflex 
action  of  the  voluntary  muscles,  so  as  to  cause  the  latter  to  con- 
tract— a  fact  within  the  painful  experience  of  all  who  have  suffered 
from  nightmare. 


xvm.]  THE  CRANIAL  XKl:\  619 

In  somnambulism  the  cerebrum  is  oapabl  iting  that  train 

of  reflex  nervous  action  which  is  0  ry  for  pi  n,  while 

tlu.  ,  Qtre  of  mntcula  (in  the  cerebellum  1)  is,  pre- 

sumably,  fully  awake ;  but  th(  still  asleep,  and  im- 

siona  made  on  it  are  not  sufficiently  fell  to  reus  ram 

to  a  comparison  of  the  difference  between  mere  ideas  or  mem 
and  sensations  derived  from  external  objei  ta 


Physiology  of  the  Cranial  Nerves. 

The  cranial  nerves  are  commonly  enumerated  as  nine  pa 
but  the  number  is  in  reality  twelve,  the  seventh  nerve  consisting 
t  d     5,  <  >f  two  nerves,  and  the  eighth  of  three.     All  arise  (super- 
ficial origin)  from  the  base  of  the  encephalon,  in  a  double  a 
which   extends   fn.in  the   under  surface  of  the  anterior  cerebral 
lobes  to  the  lower  end  of  the  medulla  oblongata.     Traced  into  the 
substance  of  the  brain  and  medulla,  the  roots  of  the  nerv<  a 
found  connected  with  various  masses  of  grey  matter,  which  arc  all 
connected  one  with  another,  and  with  the  cerebral  hemisphei 
The  roots  of  the  olfactory  tracts  are  connected  deeply  with  the 
-rex  of  the  anterior  cerebral  hemisphere,  and  probably  with  the 
corpora  striata  also.     The   optic   nerves  can   he  traced  into  the 
.  >ptic  thalami,  corpora  quadrigemina,  and  c<  >rp  >ra  geniculata.     The 
third  and  fourth  nerve  a    ris    from  grey  matter  beneath  the  c 
qnadrigemina ;   and  the  roots  of  origin  of  the  remainder  of  the 
cranial    nerves  can    he    traced    to    grey    matter    in   the    medulla 
oblongata  beneath  the  floor  of  the  fourth  ventricle,  and  in  the 
more  central  pain  of  the  medulla,  around  its  central  canal,  as  low 
down  as  the  decussation  of  the  pyramids. 

According  to  their  several  functions,  the  cranial  nerves  may  he 
thus  arranged  : — 

Nerves  of  special  sense    .     Olfactory,  optic,  auditory,  part    of    the  gloss  - 

pharyngeal,  and  of  the  lingual  branch  of  the 
fifth.* 
of  common  sensation  .     The  greater  portion  of  the  fifth. 

"'  0f  motion Third,  fourti..  ...f  the  fifth,  six tb, 

facial,  and  hypoglossal. 
Mixed  nerves     ....     Glossopharyngeal,  vagus,  and  spinal  accessory. 


620  THE  NERVOUS   SYSTEM.  [chap.  xviii. 

The  physiology  of  the  several  nerves  of  the  special  senses  will  be 
considered  with  the  organs  of  those  senses. 


Third  Nerve. 

Functions. — The  third  nerve,  or  motor  oculi,  supplies  the  levator 
palpebral  superioris  muscle,  and,  of  the  muscles  of  the  eye-ball,  all 
but  the  superior  oblique  or  trochlearis,  to  which  the  fourth  nerve  is 
appropriated,  and  the  rectus  externus  which  receives  the  sixth  nerve. 
Through  the  medium  of  the  ophthalmic  or  lenticular  ganglion,  of 
which  it  forms  what  is  called  the  short  root,  it  also  supplies  motor 
filaments  to  the  iris  and  ciliary  muscle. 

When  the  third  nerve  is  irritated  within  the  skull,  all  those 
muscles  to  which  it  is  distributed  are  convulsed.  When  it  is 
paralysed  or  divided  the  following  effects  ensue  :  (i),  the  upper 
eyelid  can  be  no  longer  raised  by  the  elevator  palpebral,  but 
droops  (ptosis)  and  remains  gently  closed  over  the  eye,  under  the 
unbalanced  influence  of  the  orbicularis  palpebrarum,  which  is 
►supplied  by  the  facial  nerve  :  (2),  the  eye  is  turned  outwards 
(external  strabismus)  by  the  unbalanced  action  of  the  rectus 
externus,  to  which  the  sixth  nerve  is  appropriated  :  and  hence, 
from  the  irregularity  of  the  axes  of  the  eyes,  double-sight  is  often 
experienced  when  a  single  object  is  within  view  of  both  the  eyes : 
(3),  the  eye  cannot  be  moved  either  upwards,  downwards,  or 
inwards  :  (4),  the  pupil  becomes  diluted  (mydriasis),  and  insensible 
to  light :  (5),  the  eye  cannot  "accommodate"  itself  for  vision  at 
short  distances. 

Contraction  and  Dilatation  of  the  Pupil. — The  relation  of 
the  third  nerve  to  the  iris  is  of  peculiar  interest.  In  ordinary 
circumstances  the  contraction  of  the  iris  is  a  reflex  action,  which 
may  be  explained  as  produced  by  the  stimulus  of  light  on  the 
retina  being  conveyed  by  the  optic  nerve  to  the  brain  (probably  to 
the  corpora  quadrigemina),  and  thence  reflected  through  the  third 
nerve  to  the  iris.  Hence  the  iris  ceases  to  act  when  either  the 
optic  or  the  third  nerve  is  divided  or  destroyed,  or  when  the 
corpora  quadrigemina  are  destroyed  or  much  compressed.  But 
when  the  optic  nerve  is  divided,  the  contraction  of  the  iris  may 
be  excited  by  irritating  that  portion  of  the  nerve  which  is  con- 
nected with  the  brain ;    and  when  the  third  nerve  is  divided,  the 


chap,  xviil]  FOUETB   NKKYK.  52r 

irritation  of  its  distal  portion  will  still  excite  the  contraction  of 
the  iris. 

The  contraction  of  the  iris  thus  shows  all  the  characters  of  a 
reflex  act,  and  in  ordinary  cases  requires  the  concurrent  action  of 
the  optic  nerve,  corpora  quadrigemina,  and  third  nerve;  and,  pro- 
bably also,  considering  the  peculiarities  of  its  perfect  mode  of 
action,  of  the  ophthalmic  ganglion.  But,  besides,  both  irides  will 
contract  their  pupils  under  the  reflected  stimulus  of  light  falling 
only  on  one  retina  or  under  irritation  of  one  optic  nerve.  Thus, 
in  blindness  of  one  eye,  its  pupil  may  contract  when  the  other  eve 
is  exposed  to  a  stronger  light  :  and  generally  the  contraction  of 
each  of  the  pupils  appears  to  be  in  direct  proportion  to  the  total 
quantity  of  light  which  stimulates  either  one  or  both  retime, 
according  as  one  or  both  eyes  are  open. 

The  iris  acts  also  in  association  with  certain  other  muscles 
supplied  by  the  third  nerve  :  thus,  when  the  eye  is  directed  in- 
wards, or  upwards  and  inwards,  by  the  action  of  the  third  nerve 
distributed  in  the  rectus  interims  and  rectus  superior,  the  iris  con- 
tracts, as  if  under  direct  voluntary  influence.  The  will  cannot, 
however,  act  on  the  iris  alone  through  the  third  nerve  ;  but  this 
aptness  to  contract  in  association  with  the  other  muscles  supplied 
by  the  third,  may  be  sufficient  to  make  it  act  even  in  total 
blindness  and  insensibility  of  the  retina,  whenever  these  muscles 
are  contracted.  The  contraction  of  the  pupils,  when  the  eyes  are 
moved  inwards,  as  in  looking  at  a  near  object,  has  probably  the 
purpose  of  excluding  those  outermost  rays  of  light  which  would  be 
too  far  divergent  to  be  refracted  to  a  clear  image  on  the  retina  ; 
and  the  dilatation  in  looking  straight  forwards  as  in  looking  at  a 
distant  object,  permits  the  admission  of  the  largest  number  of  rays, 
of  which  none  are  too  divergent  to  be  so  refracted.  (For  further 
remarks  on  the  contraction  and  dilatation  of  the  pupil,  see 
p.  702. ) 


Fourth  Nerve. 

Functions. — The  fourth  nerve,  or  Nervtis  trochlears  or  pa- 
theticus,  is  exclusively  motor,  and  supplies  only  the  trochlearis 
or  obliquus  superior  muscle  of  the  eyeball. 


622  THE  NERVOUS   SYSTEM.  [chap,  xviii. 


Fifth  or  Trigeminal  Nerve. 

Functions. — The  fifth  or  trigeminal  nerve  resembles,  as  already 
■stated,  the  spinal  nerves,  in  that  its  branches  are  derived  through 
two  roots  ;  namely,  the  larger  or  sensory,  in  connection  with  which 
is  the  Gasserian  ganglion,  and  the  smaller  or  motor  root  which  has 
no  ganglion,  and  which  passes  under  the  ganglion  of  the  sensory 
root  to  join  the  third  branch  or  division  which  issues  from  it. 
The  first  and  second  divisions  of  the  nerve,  which  arise  wholly 
from  the  larger  root,  are  purely  sensory.  The  third  division  being 
joined,  as  before  said,  by  the  motor  root  of  the  nervy,  is  of  course 
both  motor  and  sensory. 

(a.)    Motor  Functions. — Through    branches   of  the  lesser  or 
non-ganglionic  portion   of  the  fifth,  the  muscles  of  mastication, 
namely,  the  temporal,  masseter,  two  pterygoid,  anterior  part  of  the 
digastric,  and  mvlo-hvoid,  derive  their  motor  nerves.     Filaments 
are  also  supplied  to  the  tensor  tympani  and  tensor  palati.     The 
motor  function  of  these  branches  is  proved  by  the  violent  con- 
traction of  all  the  muscles  of  mastication  in  experimental  irritation 
of   the    third    or    inferior    maxillary    division    of  the    nerve ;   by 
paralysis  of  the  same  muscles,  when  it  is  divided  or  disorganised, 
or  from  any  reason  deprived  of  power ;    and  by  the  retention  of 
the  power  of  these  muscles,  when  all  those  supplied  by  the  facial 
nerve  lose  their  power  through  paralysis  of  that  nerve.     The  last 
instance   proves  best,    that   though  the  buccinator  muscle  gives 
passage  to,  and  receives  some  filaments  from,  a  buccal  branch  of 
the   inferior  division  of  the  fifth  nerve,    yet  it  derives  its  motor 
power  from  the  facial,  for  it  is  paralysed  together  with  the  other 
muscles  that  are  supplied  by  the  facial,  but  retains  its  power  when 
the  other  muscles  of  mastication  are  paralysed.     Whether,  how- 
ever,  the  branch   of  the   fifth    nerve    which    is    supplied   to  the 
buccinator  muscle  is  entirely  sensory,  or  in  part  motor  also,  must 
remain  for  the  present  doubtful.     From  the  fact  that  this  muscle, 
besides  its   other  functions,  acts  in  concert  or  harmony  with  the 
muscles  of  mastication,  in  keeping  the  food  between  the  teeth,  it 
might  be  supposed  from    analogy,    that   it   would  have  a  motor 
branch  from  the  same  nerve  that  supplies  them.     There  can  be 
no  doubt,  however,  that  the  so-called  buccal  branch  of  the  fifth  is, 


«  JIM'.    XVI  II.  J 


FIFTH    NERVE. 


623 


in  t he  main,  Bensory  ;  although  it  is  not  quite  certain  that  it  doea 

UOt  give  a  few  motor  filaments  to  the  buccinator  muscle. 

( b. )  Sensory  Functions. — Through  the  brandies  of  the  greater 
or  ganglionic  portion  of  the  fifth  nerve,  all  the  anterior  and  antero- 
lateral parts  of 
the  face  and  head, 
with  the  excep- 
tion <>f  the  skin 
of  the  parotid 
region  |  \\  hich  de- 
rives branches 
from  the  cervical 
spinal  nerves), 
acquire    common 


.sensibility  ;  and 
among  these  parts 

may  be  included 
the  organs  of  spe- 
cial sense,  from 
which  common 
sensations  arc 
conveyed  through 
the  fifth  nerve, 
and  their  spe- 
cial        sensations 

through    their   SC-    Kg.  346.— General  planof  the  branch,.*  of  the  fifth  pair.    \.—i, 

lesser  root  of  the  fifth  pair  ;  2,  greater  root  passiDg  forwards 
into  the  Gasserian  pang-lion;  3,  placed  on  the  bane  above 
the  ophthalmic  nerve,  which  is  seen  dividing  into  the  supra- 
orbital, lachrymal,  and  nasal  teaches,  the  latter  connected 
with  the  ophthalmic  ganglion ;  4,  placed  on  the  bone  close 
to  the  foramen  rotundum,  marks  the  superior  maxillary 
division,  which  is  connected  below  with  the  Bpheno-palatme 
ganglion,  and  passes  forwards  to  the  infraorbital  foramen  ; 
3,  placed  on  the  bone  over  the  foramen  ovale,  marks  the 
inferior  maxillary  nerve,  giving  off  the  anterior  auricular 
and  muscular  branches,  and  continued  by  the  inferior  dental 
to  the  lower  jaw,  and  by  the  gustatory  to  the  tongue  ;  u,  the 
submaxillary-  gland,  the  submaxillary-  ganglion  placed  above 
it  in  connection  with  the  gustatory-  nerve  ;  6,  the  chorda 
tympani  ;  7,  the  facial  nerve  issuing  from  the  stylomastoid 
foramen.     (Charles  Bell.) 


vera]  nerves  of 
special  sense.  The 
muscles,  also,  of 
the  face  and  lower 
jaw  acquire  mus- 
cular sensibility, 
through  the  fila- 
ments of  the  gan- 
glionic portion  of 
the  fifth  nerve  distributed  to  them  with  their  proper  motor  nerves. 
The  sensory  function  of  the  branches  of  the  greater  division  of  the 
fifth  nerve  is  proved,  by  all  the  usual  evidences,  such  as  their  dis- 
tribution in  parts  that  arc  sensitive  and   not  capable  of  muscular 


624  TIIE  NERVOUS   SYSTEM.  [chap.  xvnr. 

contraction,  the  exceeding  sensibility  of  some  of  these  parts,  their 
loss  of  sensation  when  the  nerve  is  paralysed  or  divided,  the  pain 
without  convulsions  produced  by  morbid  or  experimental  irrita- 
tion of  the  trunk  or  branches  of  the  nerve,  and  the  analogy 
of  this  portion  of  the  fifth  to  the  posterior  root  of  the  spinal 
nerve. 

Other  Functions. — In  relation  to  muscular  movements,  the 
branches  of  the  greater  or  ganglionic  portion  of  the  fifth  nerve 
exercise  a  manifold  influence  on  the  movements  of  the  muscles  of 
the  head  and  nice,  and  other  parts  in  which  they  are  distributed. 
They  do  so,  in  the  first  place  (a),  by  providing  the  muscles 
themselves  with  that  sensibility  without  which  the  mind,  being 
unconscious  of  their  position  and  state,  cannot  voluntarily  exer- 
cise them.  It  is,  probably,  for  conferring  this  sensibility  on  the 
muscles,  that  the  branches  of  the  fifth  nerve  communicate  so 
frequently  with  those  of  the  facial  and  hypoglossal,  and  the 
nerves  of  the  muscles  of  the  eye  ;  and  it  is  because  of  the  loss  of 
this  sensibility  that  when  the  fifth  nerve  is  divided,  animals  are 
always  slow  and  awkward  in  the  movement  of  the  muscles  of 
the  face  and  head,  or  hold  them  still,  or  guide  their  movements 
by  the  sight  of  the  objects  towards  which  they  wish  to  move. 

Again,  the  fifth  nerve  has  an  indirect  influence  on  the  muscular 
movements,  by  (b)  conveying  sensations  of  the  state  and  position 
of  the  skin  and  other  parts  :  which  the  mind  perceiving,  is  enabled 
to  determine  appropriate  acts.  Thus,  when  the  fifth  nerve  or  its. 
infra-orbital  branch  is  divided,  the  movements  of  the  lips  in 
feeding  may  cease,  or  be  imperfect.  Bell  supposed  that  the  motion 
of  the  upper  lip  in  grasping  food  depended  directly  on  the  infra- 
orbital nerve  ;  for  he  found  that,  after  he  had  divided  that  nerve 
on  both  sides  in  an  ass,  it  no  longer  seized  the  food  with  its  lipsT 
but  merely  pressed  them  against  the  ground,  and  used  the  tongue 
for  the  prehension  of  the  food.  Mayo  corrected  this  error.  He 
found,  indeed,  that  after  the  infra-orbital  nerve  had  been  divided, 
the  animal  did  not  seize  its  food  with  the  lip,  and  could  not  use  it 
well  during  mastication,  but  that  it  could  open  the  lips.  He, 
therefore,  justly  attributed  the  phenomena  in  Bell's  experiments  to 
the  loss  of  sensation  in  the  lips  ;  the  animal  not  being  able  to  feel 
the  food,  and,  therefore,  although  it  had  the  power  to  seize  it,  not 
knowing  how  or  where  to  use  that  power. 


chap,  xviii.]  FIFTH   NERVE. 

The  fifth  nerve  has  also  (e),  an  intimate  connection  with  d 
cular  movements  through  the    many  reflex  of   muse 

which  it  is  the  necessary  excitant.  Hence,  when  it  is  divided 
and  can  no  longer  convey  impressions  to  the  nervous  centres  to 
be  thence  reflected,  the  irritation  of  the  conjunctiva  produces  no 
closure  of  the  eye,  the  mechanical  irritation  of  the  nose  excites  no 
Bneezing. 

Through  its  ciliary  branches  and  the   branch  which  forms  the 
long  root  of  the  ciliary  or  ophthalmic  ganglion,  it  exercises  also 

.  some  influence  on  the  movements  of  the  iris. 

When  the  trunk  of  the  ophthalmic  portion  is  divided,  the  pupil 
becomes,  according  to  Valentin,  contracted  in  men  and  rabbits, 
and  dilated  in  cats  and  dogs  ;  but  in  all  cases,  becomes  immovable 
even  under  all  the  varieties  of  the  stimulus  of  light.  How  the 
fifth  nerve  thus  affects  the  iris  is  unexplained  ;  the  same  effects 
are  produced  by  destruction  of  the  superior  cervical  ganglion 
of  the  sympathetic,  so  that,  possibly,  they  are  due  to  the  injury 
of  those  filaments  of  the  sympathetic  which,  after  joining  the 
trunk  of  the  fifth,  at  and  beyond  the  I  rasserian  ganglion,  proceed 
with  the  branches  of  its  ophthalmic  division  to  the  iris  ;  or.  - 
R.  Hall  ingeniously  suggests,  the  influence  of  the  fifth  nerve  on 
the  movements  of  the  iris  may  be  ascribed  to  the  affection  of 
vision  in  consequence  of  the  disturbed  circulation  or  nutrition  in 
the  retina,  when  the  normal  influence  of  the  fifth  nerve  and 
ciliary  ganglion  is  disturbed.  In  such  disturbance,  increased  cir- 
culation making  the  retina  more  irritable  might  induce  extreme 
contraction  of  the  iris  ;  or  under  moderate  stimulus  of  light, 
producing  partial  blindness,  might  induce  dilatation  :  but  it  does 
not  appear  why,  if  this  be  the  true  explanation,  the  iris  should 
in  either  case  be  immovable  and  unaffected  by  the  various  degr  - 
of  light. 

Trophic  influence.  —  Furthermore,  the  morbid  effects  which 
division  of  the  fifth  nerve  produces  in  the  organs  of  special  sense, 
make  it  probable  that,  in  the  normal  state,  the  fifth  nerve  exer- 
cises some  trophic  influence  on  all  these  organs:  although,  in 
part,  the  effect  of  the  section  of  the  nerve  is  only  indirectly 
destructive  by  abolishing  sensation,  and  therefore  the  natural  safe- 
guard which  leads  to  the  protection  of  parts  from  external  injury. 
Thus,  after  such  division,  within   a   period  varying  from  twenty- 


626  THE  NERVOUS   SYSTEM.  [chap,  xviil 

four  hours  to  a  week,  the  cornea  begins  to  be  opaque  ;  then  it 
grows  completely  white  ;  a  low  destructive  inflammatory  process 
ensues  in  the  conjunctiva,  sclerotica,  and  interior  parts  of  the  eye  ; 
and  within  one  or  a  few  weeks,  the  whole  eye  may  be  quite  dis- 
organised, and  the  cornea  may  slough  or  be  penetrated  by  a  large 
ulcer.  The  sense  of  smell  (and  not  merely  that  of  mechanical 
irritation  of  the  nose),  may  be  at  the  same  time  lost  or  gravely 
impaired  ;  so  may  the  hearing,  and  commonly,  whenever  the  fifth 
nerve  is  paralysed,  the  tongue  loses  the  sense  of  taste  in  its 
anterior  and  lateral  parts,  i.e.,  in  the  portion  in  which  the  lingual 
or  gustatory  branch  of  the  inferior  maxillary  division  of  the  fifth 
is  distributed. 

In  relation  to  Taste. — The  loss  of  the  sense  of  taste  is  no  doubt 
due  (a)  to  the  lingual  branch  of  the  fifth  nerve  being  a  nerve  of 
special  sense  ;  partly,  also,  it  is  due  (b),  to  the  fact  that  this  branch 
supplies,  in  the  anterior  and  lateral  parts  of  the  tongue,  a  neces- 
sary condition  for  the  proper  nutrition  of  that  part ;  while  (c),  it 
forms  also  one  chief  link  in  the  nervous  circle  for  reflex  action,  in 
the  secretion  of  saliva  (p.  285).  But,  deferring  this  question  until, 
the  glosso-pharyngeal  nerve  is  to  be  considered,  it  may  be  observed 
that  in  some  brief  time  after  complete  paralysis  or  division  of  the 
fifth  nerve,  the  power  of  all  the  organs  of  the  special  senses  ma}' 
be  lost ;  they  may  lose  not  merely  their  sensibility  to  common 
impressions,  for  which  they  all  depend  directly  on  the  fifth  nerve, 
but  also  their  sensibility  to  their  several  peculiar  impressions  for 
the  reception  and  conduction  of  which  they  are  purposely  con- 
structed and  supplied  with  special  nerves  besides  the  fifth.  The 
facts  observed  in  these  cases  can,  perhaps,  be  only  explained  by 
the  influence  which  the  fifth  nerve  exercises  on  the  nutritive  pro- 
cesses in  the  organs  of  the  special  senses.  It  is  not  unreasonable 
to  believe,  that,  in  paralysis  of  the  fifth  nerve,  their  tissues 
may  be  the  seats  of  such  changes  as  are  seen  in  the  laxity,  the 
vascular  congestion,  oedema,  and  other  affections  of  the  skin  of  the 
face  and  other  tegumentary  parts  which  also  accompany  the 
paralysis  ;  and  that  these  changes,  which  may  appear  unimportant 
when  they  affect  external  parts,  are  sufficient  to  destroy  that 
refinement  of  structure  by  which  the  organs  of  the  special  senses 
are  adapted  to  their  functions. 

That  complete  paralysis  of  the  fifth  nerve  may  be  unaccompanied,  at  least, 


chap,  xvni.]  SIXTH   NEBYE.  627 

riderable  period,  by  injury  to  the  organs  of  special  sense,  with  the 
that  portion  of  the  tongue  which  is  supplied  by  its  gustatory 
branch,  is  well  illustrated  by  a  valuable  ease  recorded  in-  Aithaus. 

A  to  Magendie  and  Longet,  destruction  of  the  sues  more 

quickly  after  division  of  the  trunk  of  the  fifth  beyond  the  Gasserian  gan 
or  after  division  of  the  ophthalmic  branch,  than  after  division  of  the  n 
the  fifth  between  the  brain  ami  the  ganglion.    Hence  it  would  appear  as 
if  the  influence  on  nutrition  were  conveyed  in  part  through  the  filaments 
hetic,  which  join  the  branches  of  the  fifth  nerve  at  and  beyond 
1 1     -  inglion. 

The  •  of  ganglia  of  the  sympathetic  in  connection  with  all  the 

principal  divisions  of  the  fifth  nerve  where  it  gives  off  those  branches  which 
supp". .  -  of  special  sense — for  example,  the    connection    of  the 

ophthalmic  ganglion  with  the  ophthalmic  nerve  at  the  origin  of  the  ciliary 
nerves  ;  of  the  sphenopalatine  ganglion  with  the  superior  maxillary  division  , 
where  it  gives  its  branches  to  the  nose  and  the  palate  ;  of  the  otic  ganglion 
with  the  inferior  maxillary  near  the  giving  off  of  filaments  to  the  internal 
ear  :  and  of  the  sub-maxillary  ganglion  with  the  lingual  branch  of  the  fifth 
— all  these  connection-  -  __  st  that  a  peculiar  and  probably  conjoint  in- 
fluence of  the  sympathetic  and  fifth  nerves  is  exercised  in  the  nutrition  of 
the  organs  of  the  special  senses  ;  and  the  results  of  experiment  and  die 
confirm  this,  by  showing  that  the  nutrition  of  the  organs  may  be  impaired 
in  consequence  of  impairment  of  the  power  of  either  of  the  nerves. 


///  /■<  lotion  to  Sight. — A  possible  but  doubtful  connection  between 
the  fifth  nerve  and  the  .sense  of  Bight,  has  been  thought  to  be 
shown  in  eases  in  which  blows  or  other  injuries  implicating  the 

frontal  nerve  as  it  passes  over  the  brow,  are  followed  by  total  blind- 
in  the  corresponding  eye.  In  some  cases  the  blindness  occurs 
at  once,  probably  from  concussion  of  the  retina;  but  in  others  it  is 
very  slowly  progressive,  as  if  from  defective  nutrition  of  the  retina 
and  may  be  accompanied  with  inflammatory  disorganisation,  like 
that  previously  referred  to  (p.  625).  The  connection  of  the 
fifth  nerve  with  the  result  must,  however,  be  considered  very 
doubtful. 


Sixth.  Nerve. 

Functions. — The  sixth  nerve,  Nervus  oMucens  or  ocularis  ex- 
ternuSj  is  also,  like  the  fourth,  exclusively  motor,  and  supplies  only 
the  rectus  extemus  muscle. 

The  rectus  externus  is  convulsed,  and  the  eye  is  turned  out- 
wards,  when   the    sixth   nerve    is  irritated ;    and    the    muscle  is 

s  s  2 


628  THE  NERVOUS   SYSTEM.  [chap,  xviii. 

paralysed  when  the  nerve  is  divided.     In  all  such  cases  of  paralysis, 
the  eye  squints  inwards,  and  cannot  be  moved  outwards. 

In  its  course  through  the  cavernous  sinus,  the  sixth  nerve  forms 
larger  communications  with  the  sympathetic  nerve  than  any  other 
nerve  within  the  cavity  of  the  skull  does.  But  the  import  of 
these  communications  with  the  sympathetic,  and  the  subsequent 
distribution  of  its  filaments  after  joining  the  sixth  nerve,  are  quite 
unknown. 


Seventh  or  Facial  Nerve. 

Functions. — The  facial,  or  portio  dura  of  the  seventh  pair  of 
nerves,  is  the  motor  nerve  of  all  the  muscles  of  the  face,  including 
the  platysma,  but  not  including  any  of  the  muscles  of  mastication 
already  enumerated  (p.  278);  it  supplies,  also,  the  parotid  gland, 
and  through  the  connection  of  its  trunk  with  the  Vidian  nerve,  by 
the  petrosal  nerves,  some  of  the  muscles  of  the  soft  palate,  probably 
the  levator  palati  and  azygos  uvula?  ;  by  its  tympanic  branches 
it  supplies  the  stapedius  and  laxator  tympani,  and,  through  the 
otic  ganglion,  the  tensor  tympani;  through  the  chorda  tympani  it 
sends  branches  to  the  submaxillary  gland  and  to  the  lingualis  and 
some  other  muscular  fibres  of  the  tongue  ;  and  by  branches  given 
off  before  it  comes  upon  the  face,  it  supplies  the  muscles  of  the 
external  ear,  the  posterior  part  of  the  digastricus,  and  the  stylo- 
hyoideus. 

Besides  its  motor  influence,  the  facial  is  also,  by  means  of  the 
fibres  which  are  supplied  to  the  submaxillary  ami  parotid  glands, 
a  secretory  nerve.  For,  through  the  last-named  branches,  impres- 
sions may  be  conveyed  which  excite  increased  secretion  of  saliva 
(p.  286). 

Symptoms  of  Paralysis  of  Facial  Nerve. — When  the  facial 
nerve  is  divided,  or  in  any  other  way  paralysed,  the  loss  of  power  in 
the  muscles  which  it  supplies,  while  proving  the  nature  and  extent 
of  its  functions,  displays  also  the  necessity  of  its  perfection  for  the 
perfect  exercise  of  all  the  organs  of  the  special  senses.  Thus,  in  para- 
lysis of  the  facial  nerve,  the  orbicularis  palpebrarum  being  powerless, 
the  eye  remains  open  through  the  unbalanced  action  of  the  levator 
palpebr?e  ;  and  the  conjunctiva,  thus  continually  exposed  to  the  air 
and  the  contact  of  dust,  is  liable  to  repeated  inflammation,  which 


.win.]  -i.\  l.M  II    M.kVi  .  629 

may  end  in  thickening  and  opacity  of  both  its  own  tissue  and  that 
of  the  cornea.     These  changes,  however,  ensue  much  more  slowly 
than  those  which  follow   paralysis  of  the  fifth  nerve,  and  nev< 
me  destructive  character. 
Tli-  f  hearing,  also,  is  impaired  in  many  cases  of  paral; 

of  tin-  facial  nerve;  not  only  in  such  as  are  instances  of  simul- 
taneous disease  in  the  auditory  nerves,  but  in  Buch  as  may  be 
explained  by  the  loss  of  power  in  the  mi]  •"  the  internal  car. 

Tip  f  smell  is  commonly  at  the  same  time  impaired  through 

the  inability  to  draw  air  briskly  towards  the  upper  part  of  the 

nasal  cavities  in  which  part  alone  the  olfactory  nerve  is  distributed  : 
bee  draw  the  air  perfectly  in  this  direction,  the  action  of 

the  dilators  and  compressors  of  the  nostrils  should  he  perfect. 

!.  3tly,  the  3e  of  taste  is  impaired,  or  may  he  wholly  lost 
in  paralysis  of  the  facial  nerve,  provided  the  source  of  the  paral} 
he  in  s<  .me  part  of  the  nerve  between  its  origin  and  the  giving  off 
of  the  chorda  tympani.  This  result,  which  has  been  observed  in 
many  instances  of  disease  of  the  facial  nerve  in  man,  appears 
explicable  by  the  influence  which,  through  the  chorda  tympani,  it 
ses  on  the  movements  of  the  lingualis  and  the  adjacent 
muscular  fibres  of  the  tongue;  and  on  the  process  of  secretion  of 
saliva. 

Together  with  these  effects  of  paralysis  of  the  facial  nerve,  the 
muscles  of  the  face  being  all  powerless,  the  countenance  acquires 
on  the  paralysed  side  a  characteristic,  vacant  look,  from  the 
absence  of  all  expression  :  the  angle  of  the  mouth  is  lower,  and 
the  paralysed  half  of  the  mouth  looks  longer  than  that  on  the 
other  side;  the  eye  has  an  unmeaning  stare.  All  these  pecu- 
liarities increase,  the  longer  the  paralysis  lasts;  and  their 
appearance  is  exaggerated  when  at  any  time  the  muscles  of  the 
opposite  side  of  the  face  are  made  active  in  any  expression,  or  in 
any  of  their  ordinary  functions.  In  an  attempt  to  blow  or 
whistle,  one  side  of  the  mouth  and  cheek  acts  properly,  but  the 
other  side   is  motionless,    or  flaps  loosely  at  the  impulse  of  the 

oired  air  ;  so  in  trying  to  suck,  one  side  only  of  the  mouth  acta  : 
in  feeding,  the  lips  and  cheek  are  powerless,  and  food  lodg  - 
between  the  cheek  and  L'um. 


630  THE  NERVOUS   SYSTEM.  [chap,  xviii. 

Glossopharyngeal  Nerve. 

The  glossopharyngeal  nerves  (16,  fig.  347),  in  the  enumeration 
of  the  cerebral  nerves  by  numbers  according  to  the  position 
in  which  they  leave  the  cranium,  are  considered  as  divisions  of 
the  eighth  pair  of  nerves,  in  which  term  are  included  with  them 
the  pneumogastric  and  accessory  nerves.  But  the  union  of  the 
nerves  under  one  term  is  inconvenient,  although  in  some  parts  the 
glossopharyngeal  and  pneumogastric  are  so  combined  in  their 
distribution  that  it  is  impossible  to  separate  them  in  either  their 
anatomy  or  physiology. 

Distribution. — The  glosso-pharyngeal  nerve  gives  filaments 
through  its  tympanic  -branch  (Jacobson's  nerve),  to  the  fenestra 
ovalis,  and  fenestra  rotunda,  and  the  Eustachian  tube  ;  also,  to  the 
carotid  plexus,  and,  through  the  petrosal  nerve,  to  the  spheno-pala- 
tine  o-ano-lion.  After  communicating,  either  within  or  without  the 
cranium,  with  the  pneumogastric,  and  soon  after  it  leaves  the 
cranium,  with  the  sympathetic,  digastric  branch  of  the  facial,  and  the 
accessory  nerve,  the  glosso-pharyngeal  nerve  parts  into  the  two  prin- 
cipal divisions  indicated  by  its  name,  and  supplies  the  mucous  mem- 
brane of  the  posterior  and  lateral  walls  of  the  upper  part  of  the 
pharynx,  the  Eustachian  tube,  the  arches  of  the  palate,  the  tonsils 
and  their  mucous  membrane,  and  the  tongue  as  far  forwards  as  the 
foramen  caecum  in  the  middle  line,  and  to  near  the  tip  at  the  sides 
and  inferior  part. 

Functions. — The  glosso-pharyngeal  nerve  contains  some  motor 
fibres,  together  with  those  of  common  sensation  and  the  sense  of 
taste. 

1.  The  muscles  which  receive  filaments  from  the  glosso-pharyn- 
geal are  the  stylo-pharyngei,  palato-glossi,  and  constrictors  of  the 
pharynx. 

Besides  being  (2)  a  nerve  of  common  sensation  in  the  parts 
which  it  supplies,  and  a  centripetal  nerve  through  which  impres- 
sions are  conveyed  to  be  reflected  to  the  adjacent  muscles,  the 
glosso-pharyngeal  is  also  a  nerve  of  special  sensation ;  being  the 
nerve  of  taste,  in  all  the  parts  of  the  tongue  and  palate 
to  which  it  is  distributed.  After  many  discussions,  the  question, 
Which  is  the  nerve  of  taste  1 — the  lingual  branch  of  the  fifth, 
or    the    glosso-pharyngeal'?  —  may   be    most    probably    answered 


CHAP,  xvhi.]  VAGUS   XERVE.  631 

by  Btating  that  they  ore  both  nerves  of  this  special  function.  For 
very  Qumerous  experiments  and  cases  have  shown  that  when  the 
trunk  of  the  fifth  nerve  or  its  lingual  branch  is  paralysed  or 
divided,  the  senseof  taste  is  completely losl  in  the  superior  surface 
of  the  anterior  and  Lateral  parts  of  the  tongue.  The  loss  is 
instantaneous  after  division  of  the  nerve  ;  and,  therefore,  cannot 
be  ascribed  to  the  defective  nutrition  of  the  part,  though  to  this, 
perhaps,  may  be  ascribed  the  more  complete  and  general  loss  of 
the  sense  of  taste  when  the  whole  of  the  fifth  nerve  has  been 
paralysed. 

But,  on  the  other  hand,  while  the  loss  of  taste  in  the  part  of 
the  tongue  to  which  the  lingual  branch  of  the  fifth  nerve  is 
distributed  proves  that  to  be  a  gustatory  nerve,  the  fact  that  the 
sense  of  taste  is  at  the  same  time  retained  in  the  posterior  and 
postero-lateral  parts  of  the  tongue,  and  in  the  soft  palate  and  its 
anterior  arch,  to  which  (and  to  some  parts  of  which  exclusively) 
the  glosso-pharyngeal  is  distributed,  proves  that  this  also  must  be 
a  nerve  of  taste. 

Pneumogastric  or  Vagus  Nerve. 

Distribution. — The  pneumogastric  nerve,  nervus  vagus,  or 
par  vagum  (1,  fig.  347),  has,  of  all  the  cranial  and  spinal 
nerves,  the  most  various  distribution,  and  influences  the  most 
various  functions,  either  through  its  own  filaments,  or  those 
which,  derived  from  other  nerves,  are  mingled  in  its  branches. 
The  parts  supplied  by  the  branches  of  the  vagus  nerve  are 
as  follows  :  by  its  pharyngeal  branches,  which  enter  the  pha- 
ryngeal plexus,  a  large  portion  of  the  mucous  membrane,  and, 
probably,  all  the  muscles  of  the  Pharynx  ;  by  the  superior  laryn- 
geal nerve,  the  mucous  membrane  of  the  under  surface  of  the 
Epiglottis,  the  Glottis,  and  the  greater  part  of  the  Larynx,  and, 
the  crico-thyroid  muscle  ;  by  the  inferior  laryngeal  nerve,  the 
mucous  membrane  and  muscular  fibres  of  the  Trachea,  the  lower 
part  of  the  pharynx  and  larynx,  and  all  the  muscles  of  the  larynx 
except  the  crico-thyroid ;  by  oesophageal  branches,  the  mucous 
membrane  and  muscular  coats  of  the  (Esophagus.  Moreover,  the 
branches  of  the  vagus  form  a  large  portion  of  the  supply  of  nerves 
to  the  Heart  and  the  great  Arteries  through  the  cardiac  nerves, 
derived  from  both  the  trunk  and  the  recurrent    nerve  ;    to  the 


6$2 


THE  XERVOUS  SYSTEM. 


[CHAP.  XVIII. 


Fl#-  JjJ-~ T  ""„''/  the  nerves  oj  the  tight*  pair,  their  distribution  and  connections  on  the 
left  side  | —  i,  pneumogastric  nerve  in  the  neck ;  2,  ganghon  of  its  trunk  •  -i  its 
union  -with  the  spinal  accessory ;  4,  its  union  with  the  hypoglossal ;  %,  pharyngeal 
branch;  6,  superior  laryngeal  nerve;  7,  external  laryngeal;  8,  laryngeal  plexus-  o 
interior  or  recurrent  laryngeal;  10,  superior  cardiac  branch;  11,  middle  cardi'ac  •' 
12,  plexiform  part  of  the  nerve  in  the  thorax;  13,  posterior  pulmonary  plexus- 
14,  ungual  or  gustatory  nerve  of  the  inferior  maxillary  ;  is,  hypoglossal,  passme into 
the  muscles  of  the  tongue,  giving  its  thyroid-hyoid  branch,  and  uniting  with  twL?s  of 
the  lingual;  16,  glossopharyngeal  nerve;  17,  spinal  accessory  nerve,  uniting  by  its 
inner  branch  with  the  pneumogastric,  and  by  its  outer,  passing  into  the  sterno-mastoid 
muscle;  18,  second  cervical  nerve;  19,  third;  20,  fourth;  21,  origin  of  the  phrenic 
nerve,  22,  23,  fifth,  sixth,  seventh,  and  eighth  cervical  nerves,  forming  with  the  first 
dorsal  the  brachial  plexus;  24,  superior  cervical  ganglion  of  the  sympathetic-  2s 
middle  cervical  ganghon;  26,  inferior  cervical  ganglion  united  with 'the  first  dorsal 
ganglion  ;  27,  28,  29,  30,  second,  third,  fourth,  and  filth  dorsal  ganglia.  (From  Sappey 
alter  Hirschf eld  and  Leveille).  J 


«  bap.  win.]  VAGUS   NERVE. 

Lungs,  through  both  the  anterior  and  the  posterior  pulmonary 
plexuses  j  and  to  the  Stomach,  by  its  terminal  branches  passing 
over  the  walls  of  that  organ  ;  while  branches  are  also  distributed 
to  the  Liver  and  to  1  lie  Spleen. 

Communications. — Throughout  its  whole  course,  the  vagus 
contains  both  sensory  and  motor  fibres;  but  after  it  has  emerged 
from  the  skull,  and,  in  some  instances  even  sooner,  it  enters  into 
many  anastomoses  that  it  is  hard  to  say  whether  the  filaments 
ir  contains  arc,  from  their  origin,  its  own,  or  whether  they  are 
derived  from  other  aerves  combining  with  it.  This  is  particularly 
the  case  with  the  filaments  of  the  sympathetic  nerve,  which  are 
abundantly  added  to  nearly  all  its  branches.  The  likeness  to  the 
sympathetic  which  it  thus  acquires  is  further  increased  by  its  con- 
taining many  filaments  derived,  not  from  the  brain,  but  from  its 
own  petrosal  ganglia,  in  which  filaments  originate,  in  the  same 
manner  as  in  the  ganglia  of  the  sympathetic,  so  abundantly  that 
the  trunk  of  the  nerve  is  visibly  lamer  below  the  ganglia  than 
above  them  (Bidder  and  Volkmann).  Xext  to  the  sympathetic 
nerve,  that  which  most  communicates  with  the  vagus  is  the  acces- 
sory nerve,  whose  internal  branch  joins  its  trunk,  and  is  lost  in  it. 

Functions. — The  most  probable  account  of  the  particular 
functions  which  the  branches  of  the  pnenmogastric  nerve  dis- 
charge in  the  several  parts  to  which  they  are  distributed,  may  be 
drawn  from  John  Reid's  experiments  on  dogs.  They  show 
that, —  i.  The  pharyngeal  branch  is  the  principal  motor  nerve  of 
the  pharynx  and  soft  palate,  and  is  most  probably  wholly  motor  ; 
the  chief  part  of  its  motor  fibres  being  derived  "from  the  internal 
1 'ranch  of  the  accessory  nerve.  2.  The  inferior  or  recurrent 
laryngeal  nerve  is  the  motor  nerve  of  the  larynx.  3.  The  superior 
laryngeal  nerve  is  chiefly  sensory  :  the  only  muscle  supplied  by  it 
being  the  crico-thyroid.  4.  The  motions  of  the  oesophagus,  the 
stomach  and  part  of  the  small  intestines  are  dependent  on  motor 
fibres  of  the  vagus,  and  are  probably  excited  by  impressions  made 
npon  sensitive  fibres  of  the  same.  5.  The  cardiac  branches  com- 
municate, from  the  centre  in  the  medullary  channel,  impulses  (in- 
hibitory) regulating  the  action  of  the  heart.  6.  The  pulmonary 
branches  form  the  principal  channel  by  which  the  sensory  impres- 
sions on  the  mucous  surface  of  the  trachea,  bronchi  and  lungs  that 
influence  respiration  are  transmitted  to  the  medulla  oblongata  ; 


634  THE   NERVOUS    SYSTEM.  [chap,  xviii. 

and  some  fibres  also  supply  motor  influence  to  the  muscular 
portions  of  the  fibres  of  the  trachea  and  bronchi  7.  Branches 
to  the  .stomach  and  intestine  not  only  convey  motor  but  also 
vasomotor  impulses  to  those  organs.  8.  The  action  of  the 
so-called  depressor  branch  (p.  192)  in  inhibiting  the  action  of 
the  vaso-motor  centre  has  already  been  treated  of,  as  has  also  the 
influence  of  the  vagus  in  stimulating  the  secretion  of  the  salivary 
glands,  as  in  the  nausea  which  precedes  vomiting  (p.  286).  To 
summarise,  therefore,  the  many  functions  of  this  nerve,  it  may  he 
said  that  it  supplies  motor  influence  to  the  pharynx  and  oesophagus, 
to  stomach  and  small  intestine,  and  to  the  larynx,  trachea,  bronchi 
and  lung  :  sensory  and  in  pan  vaso-motor  influence  to  the  same 
regions  :  inhibitory  influence  to  the  heart  :  inhibitor}/  afferent  im- 
pulses t<»  the  vaso-motor  centre  :  excito-secretory  to  the  salivary 
glands  :   excito-motor  in  coughing,  vomiting,  &c. 

Effects  of  Section. — Division  of  both  vagi,  or  of  both  their 
recurrent  branches,  is  often  very  quickly  fatal  in  young  animals  ; 
but  in  old  animals  the  division  of  the  recurrent  nerve  is  not 
generally  fatal,  and  that  of  both  the  vagi  is  not  always  fatal, 
and,  when  it  is  so,  death  ensues  slowly.  This  difference  is, 
probably,  because,  the  yielding  of  the  cartilages  of  the  larynx  in 
young  animals  permits  the  glottis  to  be  closed  by  the  atmospheric 
pressure  in  inspiration,  and  they  are  thus  quickly  suffocated  unless 
tracheotomy  be  performed.  In  old  animals,  the  rigidity  and  promi- 
nence of  the  arytenoid  cartilages  prevent  the  glottis  from  being 
completely  closed  by  the  atmospheric  pressure  ;  even  when  all  the 
muscles  are  paralysed,  a  portion  at  its  posterior  part  remains  open, 
and  through  this  the  animal  continues  to  breathe. 

In  the  ease  of  slower  death,  after  division  of  both  the  vagi,  the 
lungs  are  commonly  found  gorged  with  blood,  (edematous,  or 
nearly  solid,  with  a  kind  of  low  pneumonia,  and  with  their 
bronchial  tubes  full  of  frothy  bloody  fluid  and  mucus,  eh,  a 
which,  in  general,  the  death  may  be  proximately  ascribed.  These 
changes  are  due,  perhaps  in  part,  to  the  influence  which  the 
nerves  exercise  on  the  movements  of  the  air-cells  and  bronchi ; 
yet,  since  they  are  not  always  produced  in  one  lung  when  its 
nerve  is  divided,  they  cannot  be  ascribed  wholly  to  the  suspension 
of  organic  nervous  influence.  Rather,  they  may  be  ascribed  to 
the  hindrance  to  the  passage  of  blood  through  the  lungs,  in  con- 


chap,  xviii.]  SPIRAL   ACCESSORY   NKUYE.  635 

sequence  of  tin*  diminished  supply  of  air  and  the  of  carbonic 

acid  in  the  air-cells  and  in  the  pulmonary  capillaries;  in  part, 
perhaps,  to  paralysis  of  the  blood-vessels,  leading  to  congestion  ; 
and  in  part,  also,  they  appear  due  to  the  passage  of  food  and 
of  the  various  secretions  of  the  mouth  and  fauces  through  the 
glottis,  which,  being  deprived  of  its  sensibility,  is  no  longer  stimu- 
lated or  closed  in  consequence  of  their  contact. 

References  to  otlier  function*  of  Vagi. — Regarding  the  influence  of  the 
also  Heart  (p.  156).  Arteries  (p.  192),  Salivary  Gland    (p.  286)> 
Glottis  and  Larynx  (p.  250),  Trachea  and  Bronchi  (p.  227).  Longs  (p.  250J, 
Pharynx  and  (Esophagus  (p.  296),  Stomach  (p.  312). 

Spinal  Accessory  Nerve. 

The  principal  branch  of  the  accessory  nerve,  its  external  branch, 
supplies  the  sterno-mastoid  and  trapezius  muscles;  and,  though 
pain  is  produced  by  irritating  it,  is  composed  almost  exclusively  of 
motor  fibres.  It  is  very  probable  that  the  accessory  nerve  gives 
Borne  motor  filaments  to  the  vagus.  For,  among  the  experiments 
made  on  this  point,  many  have  shown  that  when  the  accessory 
nerve  is  irritated  within  the  skull,  convulsive  movements  ensue 
in  some  of  the  muscles  of  the  larynx  ;  all  of  which,  as  already 
stated,  are  supplied,  apparently,  by  branches  of  the  vagus;  and 
(which  is  a  very  significant  fact)  Vrolik  states  that  in  the  chim- 
panzee the  internal  branch  of  the  accessory  does  not  join  the 
vagus  at  all,  but  goes  direct  to  the  larynx. 

Among  the  roots  of  the  accessory  nerve,  the  lower,  arising  from 
the  spinal  cord,  appear  to  be  composed  exclusively  of  motor  fibres, 
and  to  be  destined  entirely  to  the  trapezius  and  sterno-mastoid 
muscles  ;  the  upper  fibres,  arising  from  the  medulla  oblongata, 
contain  many  sensory  as  well  as  motor  fibres. 

Hypoglossal  Nerve. 

Distribution. — The  hypoglossal  or  ninth  nerve,  or  motor 
linguce,  has  a  peculiar  relation  to  the  muscles  connected  with  the 
hyoid  bone,  including  those  of  the  tongue.  It  supplies  through 
its  descending  branch  (descendens  noni),  the  stemo-hyoid,  sterno- 
thyroid, and  omodiyoid  ;  through  a  special  branch  of  the  thyro- 
hyoid, and   through   its  lingual   branches   the  genio-hyoid,  stylo- 


6^6  THE   NERVOUS   SYSTEM.  [.  u.vr.  xvm. 

glossus,    hyo-glossus,    and    genio-hyo-glossus    and    linguales.     It 
contributes,  also,  to  the  supply  of  the  submaxillary  gland. 

Functions. — The  function  of  the  hypoglossal  is  exclusively 
motor,  except  in  so  far  as  its  descending  branch  may  receive  a 
few  sensory  filaments  from  the  first  cervical  nerve.  As  a  motor 
nerve,  its  influence  on  all  the  muscles  enumerated  above  is  shown 
by  their  convulsions  when  it  is  irritated,  and  by  their  loss  of 
power  when  it  is  paralysed.  The  effects  of  the  paralysis  of  one 
hypoglossal  nerve  are,  however,  not  very  striking  in  the  tongue. 
Often,  in  cases  of  hemiplegia  involving  the  functions  of  the 
hypoglossal  nerve,  it  is  not  possible  to  observe  any  deviation  in 
the  direction  of  the  protruded  tongue ;  probably  because  the 
tongue  is  so  compact  and  firm  that  the  muscles  on  either  side, 
their  insertion  being  nearly  parallel  to  the  median  line,  can  push 
it  straight  forwards  or  turn  it  for  some  distance  towards  either 
side. 

Spinal    Nerves. 

Functions. — Little  need  be  added  to  what  has  been  already 
said  of  these  nerves  (pp.  569  to  573).  The  anterior  roots  of  the 
spinal  nerves  are  formed  exclusively  of  motor  fibres  :  the  posterior 
roots  exclusively  of  sensory  fibres.  Beyond  the  ganglia,  all  the 
spinal  nerves  are  mixed  nerves,  and  contain  as  well  sympathetic 
filaments. 

The  Sympathetic  Nerve. 

The  general  differences  between  the  fibres  of  the  cerebro-spinal 
and  sympathetic  nerves  have  been  already  stated  (pp.  544,  545), 
but  the  different  modes  of  action  of  the  two  systems  cannot  be 
referred  to  the  different  structure  of  their  fibres.  It  is  probable, 
however,  that  the  laws  of  conduction  by  the  fibres  are  in  both 
systems  the  same,  and  that  the  differences  manifest  in  the  modes 
of  action  of  the  systems  are  due  to  the  multiplication  and  sepa- 
ration of  the  nervous  centres  of  the  sympathetic  :  ganglia,  or 
nerve-centres,  being  placed  in  connection  with  the  fibres  of  the 
sympathetic  in  nearly  all  parts  of  their  course. 

Distribution. —  1.  Fibres  are  distributed  to  all  plain  or  un- 
striped  muscular  fibres,  as  those  of  the  blood-vessels  (vaso-motor 
nerves),  of  the  muscular  coats  of  the  intestines  and  other  hollow 


ohap.xviii.]  SYMPATHETIC    SYSTEM.  637 

viscera,  of  gland  ducts,  of  the    iris   and   ciliary  muscle  iii  the  eye, 

ami  elsewhere. 

The  vasomotor  fibres  conic  originally  from  the  vasomotor  centn 
in  the  medulla  oblongata  ;  and,  issuing  from  the  spinal  cord, 
communicate  with  the  prevertebral  chain  of  ganglia,  and  arc 
thence,  as  branches  from  these,  distributed  to  the  Blood-vessels. 
2.  Fibres  (accelerating)  are  distributed  to  the  Heart.  3.  Secretory 
fibres  (in  addition  to  vaso-motor)  are  distributed  to  the  salivary, 
and  presumably  to  other  secreting  glands.  4.  Inter-central  or 
inter-ganglionic  fibres.  5.  Centripetal  fibres  proceeding  to  the 
vaso-motor  centre  in  the  medulla  ;  to  the  various  sympathetic 
ganglia;  and  probably  to  all  cerebro-spinal  nerve-centres.  The 
l»  rvpheral  distribution  of  these  centripetal  fibres  is,  without 
doubt,  chiefly  in  the  parts  or  organs  to  which  the  centrifugal  fibres 
of  the  same  system  are  mainly  distributed.  But  they  are  also 
present  in  all  those  other  parts  of  the  body  which  belong  more 
especially  to  the  Cerebro-spinal  system. 

Structure. — The  sympathetic  ganglia  all  contain — (1),  nerve- 
fibres  traversing  them;  (2),  nerve-fibres  originating  in  them; 
(3),  nerve-  or  ganglion-corpuscles,  giving  origin  to  these  fibres  ; 
and  (4),  other  corpuscles  that  appear  free.  In  the  sympathetic 
ganglia  of  the  frog,  ganglion-cells  of  a  very  complicated  structure 
have  been  described  by  Beale  and  subsequently  by  Arnold.  The 
cells  are  enclosed  each  in  a  nucleated  capsule  :  they  are  pyriform 
in  shape,  and  from  the  pointed  end  two  fibres  are  given  off,  which 
gradually  acquire  the  characters  of  nerve-fibres  :  one  of  them  is 
straight,  and  the  other  (which  sometimes  arises  from  the  cell  by 
two  roots)  is  spirally  coiled  around  it. 

In  the  trunk,  and  thence  proceeding  branches  of  the  sympa- 
thetic, there  appear  to  be  always — (1),  fibres  which  arise  in  its 
own  ganglia ;  (2),  fibres  derived  from  the  ganglia  of  the  cerebral 
and  spinal  nerves  ;  (3),  fibres  derived  from  the  brain  and  spinal 
cord  and  transmitted  through  the  roots  of  their  nerves.  The 
spinal  cord,  indeed,  appears  to  be  a  large  source  of  the  fibres  of 
the  sympathetic  nerve. 

Through  the  communicating  branches  between  the  spinal  nerves 
and  the  prre-vertebral  sympathetic  ganglia,  which  have  been 
generally  called  roots  or  origins  of  the  sympathetic  nerve,  an 
interchange   is  effected   between   all  the  spinal    nerves    and  the 


chap,  xviii.]  THE    SYMPATHETIC    NERVE.  639 

sympathetic  trunks;  all  the  ganglia,  also,  which  an  ted  <>n 
the  cerebral  nerves,  have  roots  (as  they  are  called)  through  which 
filaments  of  the  cerebral  nerves  are  added  to  their  own.  So  that, 
probably,  all  sympathetic  nerves  contain  some  interim] 
cerebral  or  spinal  nerve-fibres  ;  and  all  cerebral  and  spinal  nerves 
some  filaments  derived  from  the  sympathetic  system  or  from 
ganglia.  But  the  proportions  in  which  these  filaments  arc  mingled 
are  not  uniform.  The  nerves  which  arise  from  the  brain  and 
spinal  cord  retain  throughout  their  course  and  distribution  a 
preponderance  of  cerebrospinal  fibres,  while  the  nerves  immediately 
arising  from  the  so-called  sympathetic  ganglia  probably  contain 
a  majority  of  sympathetic  fibres.  But  inasmuch  as  there  is  no 
certainty  that  in  structure  the  branches  of  cerebral  or  spinal 
nerves  differ  always  from  those  of  the  sympathetic  system,  it  is 


Fig.  3  [8. — Diagrammatic  vu  w  of  the  Sympatiu  tic  cord  of  the  right  sidi ,  showing  its  connections 
with  the  principal  cerebro-spinal  nerves  and  the  main  preaortic  plexuses.  \.  (From 
Quain's  Anatomy.) 

Cerebrospinal  nerves. — VI,  a  portion  of  the  sixth  cranial  as  it  passes  through  the  caver- 
nous sinus,  receiving  two  twigs  from  the  carotid  plexus  of  the  sympathetic  nerve ; 
O,  ophthalmic  ganglion  connected  by  a  twig  with  the  carotid  plexus:  M,  connec- 
tion of  the  spheno-palatine  ganglion  by  the  Vidian  nerve  with  the  carotid  plexus  ; 
C,  cervical  plexus  ;  Br.  brachial  plexus  ;  D  6,  sixth  intercostal  nerve  ;  D  12.  twelfth  ; 
L  3,  third  lumbar  nerve;  S  1,  first  sacral  nerve  ;  S  3,  third  ;  S  5,  fifth;  Cr,  anterior 
crural  nerve  ;  Cr',  great  sciatic  ;  pn,  pneumogastric  nerve  in  the  lower  part  of  the 
neck  ;  r,  recurrent  nerve  winding  round  the  subclavian  artery . 

Sympathetic  Cord. — c,  superior  cervical  ganglion;  <:',  second  or  middle;  c",  inferior :  from 
each  of  these  ganglia  cardiac  nerves  all  deep  on  this  side)  are  seen  descending  to  the 
cardiac  plexus;  d  1,  placed  immediately  below  the  first  dorsal  sympathetic  ganglion  ; 
d  6,  is  opposite  the  sixth  ;  I  x,  first  lumbar  ganglion ;  c  g,  the  terminal  or  coccygeal 
ganglion. 

Prteaortic  and  Visceral  Plexuses.— p  p,  pharyngeal,  and,  lower  down,  laryngeal  plexus;  pi, 
posterior  pulmonary  plexus  spreading  from  the  vagus  on  the  back  of  the  right  bron- 
chus ;  '•  a,  on  the  aorta,  the  cardiac  plexus,  towards  which,  in  addition  to  the  cardiac 
nerves  from  the  three  cervical  sympathetic  ganglia,  other  branches  are  seen  descend- 
ing from  the  vagus  and  recurrent  nerves  ;  co,  right  or  posterior,  and  co',  left  or  ante- 
rior coronary  plexus ;  o,  oesophageal  plexus  in  long  meshes  on  the  gullet ;  sp,  great 
splanchnic  nerve  formed  by  branches  from  the  fifth,  sixth,  seventh,  eighth,  and  nintli 
dorsal  ganglia  ;  — ,  small  splanchnic  from  the  ninth  and  tenth  ;  +  -f,  smallest  or  third 
splanchnic  from  the  eleventh :  the  first  and  second  of  these  are  shown  joining  the 
solar  plexus,  c  0;  the  third  descending  to  the  renal  plexus,  r  1  ;  connecting  branches 
between  the  solar  plexus  and  the  vagi  are  also  represented  :  pn',  above  the  place  where 
the  right  vagus  passes  to  the  lower  or  posterior  surface  of  the  stomach  ;  pn" ,  the  left 
distributed  on  the  anterior  or  upper  surface  of  the  cardiac  portion  of  the  organ  :  from 
the  solar  plexus  large  branches  are  seen  surrounding  the  arteries  of  the  cceliac  axis, 
and  descending  to  m  1,  the  superior  mesenteric,  plexus  ;  opposite  to  this  is  an  indica- 
tion of  the  suprarenal  plexus  ;  belowrc  the  renal  plexus,  the  spermatic  plexus  is 
also  indicated;  a  o,  on  the  front  of  the  aorta,  marks  the  aortic  plexus,  formed  by 
nerves  descending  from  the  solar  and  superior  mesenteric  plexuses  and  from  the  lum- 
bar ganglia  :  mi,  the  inferior  mesenteric  plexus  surrounding  the  corresponding  artery ; 
hy,  hypogastric  plexus  placed  between  the  common  iliac  vessels,  connected  above  with 
the  aortic  plexus,  receiving  nerves  from  the  lower  lumbar  ganglia,  and  dividing  below 
into  the  right  and  left  pelvic  or  inferior  hypogastric  plexuses;  pL  the  right  pelvic 
plexus;  from  this  the  nerves  descending  are  joined  by  those  from  the  plexus  on  the 
superior  hemorrhoidal  vessel*,  /»*".  by  sympathetic  nerves  from  the  sacral  ganglia,  and 
by  numerous  visceral  nerves  from  the  third  and  fourth  sacral  spinal  nerves,  and  there 
are  thus  formed  the  rectal,  vesical,  and  other  plexuses,  which  ramify  upon  the  viscera 
from  behind  forwards  and  from  below  upwards,  as  towards  ir,  and  v,  the  rectum  and 
bladder. 


640  THE    NERVOUS    SYSTEM.  [chap,  xviii. 

impossible  in  the  present  state  of  our  knowledge  to  be  sure  of  the 
source  of  fibres  which  from  their  structure  might  lead  the 
observer  to  believe  that  they  arose  from  the  brain  or  spinal  cord 
on  the  one  hand,  or  from  the  sympathetic  ganglia  on  the  other. 
In  other  words,  although  the  large  white  medullated  fibres  are 
especially  characteristic  of  cerebro-spinal  nerves,  and  the  pale  or 
non-medullated  fibres  of  a  sympathetic  nerve,  in  which  they 
largely  preponderate,  there  is  no  certainty  to  be  obtained  in  a 
doubtful  case,  of  whether  the  nerve-fibre  is  derived  from  one  or 
the  other,  from  mere  examination  of  its  structure.  It  may  be 
derived  from  either  source. 

Functions. — It  may  be  stated  generally  that  the  sympathetic 
nerve-fibres  are  simple  conductors  of  impressions,  as  are  those  of 
the  Cerebro-spinal  system  j  and  that  the  ganglionic  centres  have 
(each  in  its  appropriate  sphere)  the  like  powers  both  of  conducting, 
transferring,  reflecting,  and  possibly  of  augmenting  or  of  inhibiting 
impressions  made  on  them. 

The  power  possessed  by  the  sympathetic  ganglia  of  conducting 
impressions  is  sufficiently  proved  in  disease,  as  when  any  of  the 
viscera,  usually  unfelt,  give  rise  to  sensations  of  pain,  or  when  a 
part  not  commonly  subject  to  mental  influence  is  excited  or  re- 
tarded in  its  actions  by  the  various  conditions  of  the  mind;  for  in 
all  these  cases  impressions  must  be  conducted  to  and  fro  through 
the  whole  distance  between  the  part  and  the  spinal  cord  and  brain. 
So,  also,  in  experiments,  now  more  than  sufficiently  numerous, 
irritations  of  the  semilunar  ganglia,  the  splanchnic  nerves,  the 
thoracic,  hepatic,  and  other  ganglia  and  nerves,  have  elicited 
expressions  of  pain,  and  have  excited  movements  in  the  muscular 
organs  supplied  from  the  irritated  part. 

In  the  case  of  pain,  or  of  movements  affected  by  mental  con- 
ditions, it  may  be  supposed  that  the  conduction  of  impressions  is 
effected  through  the  cerebro-spinal  fibres  which  are  mingled  in 
all,  or  nearly  all,  parts  of  the  sympathetic  nerves.  There  are  no 
means  of  deciding  this  ;  but  if  it  be  admitted  that  the  conduction 
is  effected  through  the  cerebro-spinal  nerve-fibres,  then,  whether 
or  not  they  pass  uninterruptedly  between  the  brain  or  spinal  cord 
and  the  part  affected,  it  must  be  assumed  that  their  mode  of 
conduction  is  modified  by  the  ganglia.  For,  if  such  cerebro- 
spinal fibres   are   conducted   in  the   ordinary  manner,  the  parts 


chap,  xviii.]       FUNCTIONS    OF    SYMPATHETIC    NERVE.  641 

should  be  always  sensible  and  liable  to  the  influence  of  the  will, 
and  impressions  should  be  conveyed  to  and  fro  instantaneously. 
But  this  is  not  the  ease  ;  on  the  contrary,  through  the  branches  of 
the  sympathetic  nerve  and  its  ganglia,  none  but  intense  impres- 
sions, or  impressions  exaggerated  by  the  morbid  excitability  of  the 
nerves  or  ganglia,  can  be  conveyed. 

Respecting  the  general  action  of  the  ganglia  of  the  sympathetic 
nerve,  in  reflex  or  other  actions,  little  need  be  said  here,  since 
they  may  be  taken  as  examples  by  which  to  illustrate  the  common 
modes  of  action  of  all  nerve-centres  (see  p.  558).  Indeed,  com- 
plex as  the  sympathetic  system,  taken  as  a  whole,  is,  it  presents 
in  each  of  its  parts  a  simplicity  not  to  be  found  in  the  cerebro- 
spinal system  :  for  each  ganglion  with  afferent  and  efferent  nerves 
forms  a  simple  nervous  system,  and  might  serve  for  the  illus- 
tration of  all  the  nervous  actions  with  which  the  mind  is 
unconnected. 

The  parts  principally  supplied  with  sympathetic  nerves  are 
usually  capable  of  none  but  involuntary  movements,  and  when 
the  mind  acts  on  them  at  all,  it  is  only  through  the  strong  excite- 
ment or  depressing  influence  of  some  passion,  or  through  some 
voluntary  movement  with  which  the  actions  of  the  involuntary 
part  are  commonly  associated.  The  heart,  stomach,  and  intes- 
tines are  examples  of  these  statements;  for  the  heart  and  stomach, 
though  supplied  in  large  measure  from  the  pneumogastric  nerves, 
yet  probably  derive  through  them  few  filaments  except  such  as 
have  arisen  from  their  ganglia,  and  are  therefore  of  the  nature  of 
sympathetic  fibres. 

The  parts  which  are  supplied  with  motor  power  by  the  sym- 
pathetic nerve  continue  to  move,  though  more  feebly  than  before, 
when  they  are  separated  from  their  natural  connections  with  the 
rest  of  the  sympathetic  system,  and  wholly  removed  from  the 
body.  Thus,  the  heart,  after  it  is  taken  from  the  body,  continues 
to  beat  in  Mammalia  for  one  or  two  minutes,  in  reptiles  and 
Amphibia  for  hours  ;  and  the  peristaltic  motions  of  the  intestine 
continue  under  the  same  circumstances.  Hence  the  motions  of  the 
parts  supplied  with  nerves  from  the  sympathetic  are  shown  to 
be,  in  a  measure,  independent  of  the  brain  and  spinal  cord ;  this 
independent  maintenance  of  their  action  being,  without  duobt, 
due  to  the  fact  that  they  contain,  in  their  own  substance,   the 

t  1 


642  THE    NERVOUS    SYSTEM.  [chap,  xviii. 

apparatus  of  ganglia  and  nerve-fibres  by  which  their  motions  are 
immediately  governed. 

It  seems  to  be  a  general  rule,  at  least  in  animals  that  have 
both  cerebro-spinal  and  sympathetic  nerves  much  developed,  that 
the  involuntary  movements  excited  by  stimuli  conveyed  through 
ganglia  are  orderly  and  like  natural  movements,  while  those 
excited  through  nerves  without  ganglia  are  convulsive  and  dis- 
orderly ;  and  the  probability  is  that,  in  the  natural  state,  it  is 
through  the  same  ganglia  that  natural  stimuli,  impressing  centri- 
petal nerves,  are  reflected  through  centrifugal  nerves  to  the  in- 
voluntary muscles.  As  the  muscles  of  respiration  are  maintained 
in  uniform  rhythmic  action  chiefly  by  the  reflecting  and  combining 
power  of  the  medulla  oblongata,  so  are  those  of  the  heart,  stomach, 
and  intestines,  by  their  several  ganglia.  And  as  with  the  ganglia 
of  the  sympathetic  and  their  nerves,  so  with  the  medulla  oblon- 
gata and  its  nerves  distributed  to  the  respiratory  muscles, — if 
these  nerves  of  the  medulla  oblongata  itself  be  directly  stimulated, 
the  movements  that  follow  are  convulsive  and  disorderly ;  but  if 
the  medulla  be  stimulated  through  a  centripetal  nerve,  as  when 
cold  is  applied  to  the  skin,  then  the  impressions  are  reflected  so 
as  to  produce  movements  which,  though  they  may  be  very  quick 
and  almost  convulsive,  are  yet  combined  in  the  plan  of  the  proper 
respiratory  acts. 

Among  the  ganglia  of  the  sympathetic  nerves  to  which  this 
co-ordination  of  movements  is  to  be  ascribed,  must  be  reckoned, 
not  those  alone  which  are  on  the  principal  trunks  and  branches 
of  the  sympathetic  external  to  any  organ,  but  those  also  which 
lie  in  the  very  substance  of  the  organs  ;  such  as  those  of  the 
heart  (p.  155).  Those  also  may  be  included  which  have  been 
found  in  the  mesentery  close  by  the  intestines,  as  well  as  in  the 
muscular  and  sub-mucous  tissue  of  the  stomach  and  intestinal 
canal  (pp.  302,  315),  and  in  other  parts.  The  extension  of  dis- 
coveries of  such  ganglia  will  probably  diminish  yet  further  the 
number  of  instances  in  which  the  involuntary  movements  appear 
to  be  effected  independently  of  nervous  influence. 

Respecting  the  influence  of  the  sympathetic  system  on  various 
physiological  processes,  see  Heart  (p.  158),  Arteries  (p.  190), 
Animal  Heat  (p.  391),  Salivary  Glands  (p.  287),  Stomach  (p.  312), 
Intestines  (p.  316).     These   are  parts  which  have  been  specially 


i -II.M-.  .win. J  INFLUENCE    ON    NUTBITION.  643 

investigated.  But  they  are  not  in  any  way  exceptional  All 
physiological  processes  must,  of  necessity,  either  directly  or 
through  vasomotor  fibres,  be  under  the  influence  of  the  Sympa- 
thetic Bystem. 

Influence  of  the  Nervous  System  on  Nutrition. — It  has 
been  held  that  the  nervous  system  cannot  be  essential  to  a  healthy 
course  of  nutrition,  because  in  plants  and  the  early  embryo,  and  in 
the  lowest  animals,  in  which  no  nervous  system  is  developed,  nutri- 
tion goes  on  without  it.  But  this  is  no  proof  that  in  animals 
which  have  a  nervous  system,  nutrition  may  be  independent  of  it  ; 
rather,  it  may  be  assumed,  that  in  ascending  development,  as  one 
system  after  another  is  added  or  increased,  so  the  highest  (and, 
highest  of  all,  the  nervous  system)  will  always  be  inserted  and 
blended  in  a  more  and  more  intimate  relation  with  all  the  rest  : 
according  to  the  general  law,  that  the  interdependence  of  parts 
augments  with  their  development. 

The  reasonableness  of  this  assumption  is  proved  by  many  facts 
showing  the  influence  of  the  nervous  system  on  nutrition,  and  by 
the  most  striking  of  these  facts  being  observed  in  the  higher 
animals,  and  especially  in  man.  The  influeuce  of  the  mind  in 
the  production,  aggravation,  and  cure  of  organic  diseases  is 
matter  of  daily  observation,  and  a  sufficient  proof  of  influence 
exercised  on  nutrition  through  the  nervous  system. 

Independently  of  mental  influence,  injuries  either  to  portions 
of  the  nervous  centres,  or  to  individual  nerves,  are  frequently 
followed  by  defective  nutrition  of  the  parts  supplied  by  the  injured 
nerves,  or  deriving  their  nervous  influence  from  the  damaged 
portions  of  the  nervous  centres.  Thus,  lesions  of  the  spinal  cord 
are  sometimes  followed  by  mortification  of  portions  of  the  para- 
lysed parts  ;  and  this  may  take  place  very  quickly,  as  in  a  case 
in  which  the  ankle  sloughed  within  twenty-four  hours  after  an 
injury  of  the  spine.  After  such  lesions  also,  the  repair  of  injuries 
in  the  paralysed  parts  may  take  place  less  completely  than  in 
others;  so,  in  a  case  in  which  paraplegia  was  produced  by  fracture 
of  the  lumbar  vertebrae,  and,  in  the  same  accident,  the  humerus 
and  tibia  were  fractured.  The  former  in  due  time  united  :  the 
latter  did  not.  The  same  fact  was  illustrated  by  some  experi- 
ments, in  which  having,  in  salamanders,  cut  off  the  end  of  the 
tail,  and  then  thrust  a  thin  wire   some  distance  up  the   spinal 

t  t  2 


644  TJ1E    NERVOUS    SYSTEM.  [chap,  xviii" 

canal,  so  as  to  destroy  the  cord,  it  was  found  that  the  end  of  the 
tail  was  reproduced  more  slowly  than  in  other  salamanders  in 
whom  the  spinal  cord  was  left  uninjured  above  the  point  at  which 
the  tail  was  amputated.  Illustrations  of  the  same  kind  are 
furnished  by  the  several  cases  in  which  division  or  destruction  of 
the  trunk  of  the  trigeminal  nerve  has  been  followed  by  incomplete 
and  morbid  nutrition  of  the  corresponding  side  of  the  face  ;  ulce- 
ration of  the  cornea  being  often  directly  or  indirectly  one  of  the 
consequences  of  such  imperfect  nutrition.  Part  of  the  wasting 
and  slow  degeneration  of  tissue  in  paralysed  limbs  is  probably 
referable  also  to  the  withdrawal  of  nervous  influence  from 
them ;  though,  perhaps,  more  is  due  to  the  want  of  use  of  the 
tissues. 

Undue  irritation  of  the  trunks  of  nerves,  as  well  as  their 
division  or  destruction,  is  sometimes  followed  by  defective  or 
morbid  nutrition.  To  this  may  be  referred  the  cases  in  which 
ulceration  of  the  parts  supplied  by  the  irritated  nerves  occurs 
frequently,  and  continues  so  long  as  the  irritation  lasts.  Further 
evidence  of  the  influence  of  the  nervous  system  upon  nutrition  is 
furnished  by  those  cases  in  which,  from  mental  anguish,  or  in 
severe  neuralgic  headaches,  the  hair  becomes  grey  very  quickly, 
or  even  in  a  few  horn's. 

So  many  and  varied  facts  leave  little  doubt  that  the  nervous 
system  exercises  an  influence  over  nutrition  as  over  other  organic 
processes ;  arid  they  cannot  be  easily  explained  by  supposing  that 
the  changes  in  the  nutritive  processes  are  only  due  to  the  varia- 
tions in  the  size  of  the  blood-vessels  supplying  the  affected  parts, 
although  this  is,  doubtless,  one  important  element  in  producing 
the  result. 

The  question  remains,  through  what  class  of  nerves  is  the 
influence  exerted  ?  "When  defective  nutrition  occurs  in  parts 
rendered  inactive  by  injury  of  the  motor  nerve  alone,  as  in  the 
muscles  and  other  tissues  of  a  paralysed  face  or  limb,  it  may 
appear  as  if  the  atrophy  were  the  direct  consequence  of  the  loss 
of  power  in  the  motor  nerves ;  but  it  is  more  probable  that  the 
atrophy  is  the  consequence  of  the  want  of  exercise  of  the  parts ; 
for  if  the  muscles  be  exercised  by  artificial  irritation  of  their 
nerves  their  nutrition  will  be  less  defective.  The  defect  of  the 
nutritive  process  which  ensues  in  the  face  and  other  parts,  how- 


.hat.  xvin. J  INFLUENCE    ON    KUTBITION.  645 

.  in  consequence  of  destruction  of  the  trigeminal  oerve,  cannot 
be  referred  to  loss  of  influence  of  any  motor  nerves  ;  for  the 
motor-nerves  of  the  tare  and  eye,  as  well  as  the  olfactory  and 
optic,  have  do  share  in  the  defective  nutrition  which  follows 
injury  of  the  trigeminal  nerve;  and  one  or  all  of  them  maybe 
destroyed  without  any  direct  disturbance  of  the  nutrition  of  the 
parts  they  severally  supply. 

It  must  be  concluded,  therefore,  that  the  influence  whici. 
exercised  by  nerves  over  the  nutrition  of  parts  to  which  they  are 
distributed  is  to  be  referred,  in  part  or  altogether,  either  to  the 
nerves  of  common  sensation,  or  to  the  vaso-motor  nerves,  or,  as 
it  is  by  some  supposed,  to  nerve-fibres  (trophic  nerves),  which 
preside  specially  over  the  nutrition  of  the  tissues  and  organs  to 
which  they  are  supplied. 

It  is  not  at  present  possible  to  say  whether  the  influence  on 
nutrition  is  exercised  through  the  cerebro-spinal  or  through  the 
sympathetic  nerves,  which,  in  the  parts  on  which  the  observation 
has  been  made,  are  generally  combined  in  the  same  sheath.  The 
truth  perhaps  is,  that  it  may  be  exerted  through  either  or  both 
of  these  nerves.  The  defect  of  nutrition  which  ensues  after  lesion 
of  the  spinal  cord  alone,  the  sympathetic  nerves  being  uninjured, 
and  the  general  atrophy  which  sometimes  occurs  in  consequence 
of  diseases  of  the  brain,  seem  to  prove  the  influence  of  the  cerebro- 
spinal system :  while  the  observation  that  inflammation  of  the 
eye  is  a  constant  result  of  ligature  of  the  sympathetic  nerve  in 
the  neck,  and  many  other  observations  of  a  similar  kind,  exhibit 
verv  well  the  influence  of  the  latter  nerve  in  nutrition. 


646  THE    SENSES.  [chap.  xix. 


CHAPTER  XIX. 

THE   SENSES. 

Through  the  medium  of  the  Nervous  system  the  mind  obtains 
a  knowledge  of  the  existence  both  of  the  various  parts  of  the  body, 
and  of  the  external  world.  This  knowledge  is  based  upon  sensa- 
tions resulting  from  the  stimulation  of  certain  centres  in  the  brain 
by  irritations  conveyed  to  them  by  afferent  (sensory)  nerves. 
Under  normal  circumstances,  the  following  structures  are  neces- 
sary for  sensation  :  (a)  A  peripheral  organ  for  the  reception  of  the 
impression  ;  (b)  a  nerve  for  conducting  it ;  (c)  a  nerve-centre  for 
feeling  or  perceiving  it. 

Classification  of  Sensations. — Sensations  may  be  conve- 
niently classed  as  (1)  common  and  (2)  special. 

(1.)  Common  sensations. — Under  this  head  fall  all  those  general 
sensations  which  cannot  be  distinctly  localized  in  any  particular 
part  of  the  bod}',  such  as  Fatigue,  Discomfort,  Faintness,  Satiety, 
together  with  Hunger  and  Thirst,  in  which,  in  addition  to  a 
general  discomfort,  there  is  in  many  persons  a  distinct  sensation 
referred  to  the  stomach  or  fauces.  In  this  class  must  also  be 
placed  the  various  irritations  of  the  mucous  membrane  of  the 
bronchi,  which  give  rise  to  coughing,  and  also  the  sensations 
derived  from  various  viscera  indicating  the  necessity  of  expelling 
their  contents ;  e.g.,  the  desire  to  defalcate,  to  urinate,  and,  in  the 
female,  the  sensations  which  precede  the  expulsion  of  the  foetus. 
We  must  also  include  such  sensations  as  itching,  creeping,  tick- 
ling, tingling,  burning,  aching,  etc.,  some  of  which  come  under  the 
head  of  pain  :  they  will  be  again  referred  to  in  describing  the  sense 
of  Touch.  It  is  impossible  to  draw  a  very  clear  line  of  demarca- 
tion between  many  of  the  common  sensations  above  mentioned, 
and  the  sense  of  Touch,  which  forms  the  connecting  link  between 
the  general  and  special  sensations.  Touch  is,  indeed,  usually 
classed  with  the  special  senses,  and  will  be  considered  in  the  same 
group  with  them  ;  yet  it  differs  from  them  in  being  common  to 
many   nerves;    e.g.,    all    the    sensory  spinal  nerves,    the    vagus, 


chap,  xix.]  SPECIAL    SENSATIONS,  647 

glossopharyngeal,  and  fifth  cerebral  nerves,  and  in  its  impressions 
being  communicable  through  many  organs.     Among  common 
Bations  must   also  be  ranked  the  nwtcular  sense,  winch   has  been 

already  alluded  to.      It  is  by  means  of  this  sense    that  we    become 

aware  of  the  condition  of  contraction  or  relaxation  of  the  various 
muscles  and  groups  of  muscles,  and  thus  obtain  the  information 
necessary  for  their  adjustment  to  various  purposes — standing, 
walking,  grasping,  etc  This  muscular  sensibility  is  shown  in  our 
power  to  estimate  the  differences  between  weights  by  the  different 
muscular  efforts  neeessary  to  raise  them.  Considerable  delicacy 
may  be  attained  by  practice,  and  the  difference  between  19',  oz. 
in  one  hand  and  20  oz.  in  the  other  is  readily  appreciated 
(Weber). 

This  sensibility  with  which  the  muscles  arc  endowed  must  be 
carefully  distinguished  from  the  sense  of  contact  and  of  pressure, 
of  which  the  skin  is  the  organ.  When  standing  erect,  we  can  feel 
the  ground  (contact),  and  further  there  is  a  sense  of  pressure,  due 
to  our  feet  being  pressed  against  the  ground  by  the  weight  of  the 
body.  Both  these  are  derived  from  the  skin  of  the  sole  of  the  foot. 
If  now  we  raise  the  body  on  the  toes,  we  are  conscious  (muscular 
sense)  of  a  muscular  effort  made  by  the  muscles  of  the  calf,  which 
overcomes  a  certain  resistance. 

(2.)  Special  Sensations. — Including  the  sense  of  touch,  the 
special  senses  are  five  in  number — Touch,  Taste,  Smell,  Hearing, 
Sight. 

Difference  between  Common  and  Special  Sensations.— 
The  most  important  distinction  between  common  and  special 
sensations  is  that  by  the  former  we  are  made  aware  of  certain 
conditions  of  various  parts  of  our  bodies,  while  from  the  latter 
we  gain  our  knowledge  of  the  external  world  also.  This  dif- 
ference will  be  clear  if  we  compare  the  sensations  of  pain  and 
touch,  the  former  of  which  is  a  common,  the  latter  a  special 
sensation.  "  If  we  place  the  edge  of  a  sharp  knife  on  the  skin, 
we  feel  the  edge  by  means  of  our  sense  of  touch  ;  we  perceive  a 
sensation,  and  refer  it  to  the  object  which  has  caused  it.  But  as 
soon  as  we  cut  the  skin  with  the  knife,  we  feel  pain,  a  feeling 
which  we  no  longer  refer  to  the  cutting  knife,  but  which  we  feel 
within  ourselves,  and  which  communicates  to  us  the  fact  of  a 
change  of  condition   in  our  own  body.     By  the  sensation  of  pain 


648  THE    SENSES.  [chap.  xix. 

we  are  neither  able  to  recognise  the  object  which  caused  it,  nor  its 
nature  "  (Weber). 

General  Characteristics  :  Seat. — In  studying  the  phenomena 
of  sensation,  it  is  important  clearly  to  understand  that  the  Sen- 
sorium, or  seat  of  sensation,  is  in  the  Brain,  and  not  in  the  parti- 
cular organ  (eye,  ear,  etc.)  through  which  the  sensory  impression 
is  received.  In  common  parlance  we  are  said  to  see  with  the  eye, 
hear  with  the  ear,  etc.,  but  in  reality  these  organs  are  only 
adapted  to  receive  impressions  which  are  conducted  to  the  sen- 
sorimn,  through  the  optic  and  auditory  nerves  respectively,  and 
there  give  rise  to  sensation. 

Hence,  if  the  optic  nerve  is  severed  (although  the  eye  itself  is 
perfectly  uninjured),  vision  is  no  longer  possible ;  since,  although 
the  image  falls  on  the  retina  as  before,  the  sensory  impression  can 
no  longer  be  conveyed  to  the  sensorium.  "When  any  given  sen- 
sation is  felt,  all  that  we  can  with  certainty  affirm  is  that  the  sen- 
sorium in  the  brain  is  excited.  The  exciting  cause  maybe  (in  the 
vast  majority  of  cases  is),  some  object  of  the  external  world  (objec- 
tive sensation) ;  or  the  condition  of  the  sensorium  may  be  due  to 
some  excitement  within  the  brain,  in  which  case  the  sensation  is 
termed  subjective.  The  mind  habitually  refers  sensations  to  external 
causes;  and  hence,  whenever  they  are  subjective  (due  to  causes 
within  the  brain),  we  can  hardly  divest  ourselves  of  the  idea  of  an 
external  cause,  and  an  illusion  is  the  result. 

Illusions. — Numberless  examples  of  such  illusions  might  be  quoted.  As 
familiar  cases  may  be  mentioned,  humming  and  buzzing  in  the  ears  caused 
by  some  irritation  of  the  auditory  nerve  or  centre,  and  even  musical  sounds 
and  voices  (sometimes  termed  auditory  spectra)  ;  also  so-called  optical 
illusions  :  persons  and  other  objects  are  described  as  being  seen,  although 
not  present.  Such  illusions  are  most  strikingly  exemplified  in  cases  of 
delirium  tremens  or  other  forms  of  delirium,  in  which  cats.  rats,  creeping 
loathsome  forms,  etc..  are  described  by  the  patient  as  seen  with  great 
vividness. 

Causes  of  Illusions. — One  uniform  internal  cause,  which  may 
act  on  all  the  nerves  of  the  senses  in  the  same  manner,  is  the 
accumulation  of  blood  in  their  capillary  vessels,  as  in  congestion 
and  inflammation.  This  one  cause  excites  in  the  retina,  while  the 
eyes  are  closed,  the  sensations  of  light  and  luminous  flashes  ;  in 
the  auditory  nerve,  the  sensation  of  humming  and  ringing  sounds  ; 
in  the  olfactorv  nerve,  the  sense  of  odours ;  and  in  the  nerves  of 


chap,  xix.]  SPECIAL    BEN8ATIOX8. 

feeling,  the  Bensation  of  pain.     In  the  .  also,  a  oar 

substance,  introduced  into  the  blood,  excites  in  th< 

peculiar  symptoms :  in  the  optic  nerves,  the  appearanc 
luminous  Bparks   before  th<  ;  in  the  auditory  □ 

nitns  aurium  "  :  and  in  the  common  sensory  nerves,  the-  sensation 
of  creeping  over  the  suri  S  ,  also,  am     _  -.the 

stimulus  of  electricity,  or  the  mechanical  influence  of  a  blow,  con- 
in,  or  pressure,  excites  in  the  eve  the  Bensation  of  light  ;in<l 
colours;  in  the  <  a    us    of  a  loud  sound  or  of  ringing ;  in  the 

.  a  saline  or  acid  taste  :  and  in  the  other  parts  of  the  1 
a  perception  of  peculiar  jarr    e        f  the  mechanical  impress 
like  it. 
Sensations  and  Perceptions. — The  habit  of  constantly  refer- 
ring our  sensations  to  external  causes,  lea  Is     i  to  interpret  the 
various  modifications  which  external  objects  produce  in  our  sensa- 
»f  the  external        lies  i     .  [selves.     Thus  we 
speak  of  certain  substances  as  possess    _  -   agreeable  taste  and 

smell  :  whereas,   the  fact   is,  their  taste  and   smell  are   only 

_     eable  to  us.      It  is  evident,  however,  that  on  this    habit  of 
referring  our  sensations  to  causes  outside  ourseb  rception), 

3  the  reality  of  the  external  world  t  us  j  and  more  espe- 
cially is  this  the  case  with  the  sens  -  f  touch  and  sight.  By  the 
co-operation  of  these  tw<  senses  aided  by  the  others,  we  are  enabled 
gradually  to  attain  a  know]  _  f  external  objects  which  daily  ex- 
perience confirms,  until  we  come  to  place  unbounded  confidence  in 
what  is  termed  the  ''evidence  oft!     -     a  s. 

Judgments. — We  must  draw  a  distinction  |    -  sensa- 

.  and  the  judgments  based,  often  unc  -  isly,  upon  them. 
Thus,  in  looking  at  a  near  object,  we  unc  a  nsly  estimate  its 
distance,  and  say  it  -  dob  to  be  ten  <»r  twelve  feet  off:  hut  the 
estimate  "fits  distance  is  in  reality  *  judgment  based  on  many 
tilings  -  s  the  appearance  of  the  object  itself:  among  which 
may  be  mentioned  the  number  of  intervening  i  ts,  the  number 
of  steps  which  from  past  experience  we  know  we  must  take  before 
we  could  touch  it,  and  many  others. 

Symptoms  of  Irritation  of   Nerves   of  Special   Sense.— 

Irritation  of  the  optic  nerve,  as  by  cutting  it,  invariably  produces 

oration  of  light,  of  the  auditory  nerv         a  nsation  of  some 

modification  of  sound.     Doubtless  -  $t      I  sensations  depend 


650  THE    SENSES.  [chap.  xix. 

not  on  any  speciality  in  the  structure  of  the  nerves  of  special 
sense,  but  on  the  nature  of  their  connections  in  the  sensorium. 

Experiments  seem  to  have  proved  that  none  of  these  nerves 
possess  the  faculty  of  common  sensibility.  Thus,  Magendie 
observed  that  when  the  olfactory  nerves,  laid  bare  in  a  dog,  were 
pricked,  no  signs  of  pain  were  manifested ;  and  other  experiments 
of  his  seem  to  show  that  both  the  retina  and  optic  nerve  are 
insusceptible  of  pain.  Further,  the  optic  nerve  is  insusceptible  to 
the  stimulus  of  light  when  severed  from  its  connection  with  the 
retina,  which  alone  is  adapted  to  receive  luminous  impressions. 

Sensation  of  Motion  is,  like  motion  itself,  of  two  kinds, — 
progressive  and  vibratory.  The  faculty  of  the  perception  of  pro- 
gressive motion  is  possessed  chiefly  by  the  senses  of  vision, 
touch,  and  taste.  Thus  an  impression  is  perceived  travelling 
from  one  part  of  the  retina  to  another,  and  the  movement  of  the 
image  is  interpreted  by  the  mind  as  the  motion  of  the  object. 
The  same  is  the  case  in  the  sense  of  touch  ;  so  also  the  movement 
of  a  sensation  of  taste  over  the  surface  of  the  organ  of  taste,  can 
be  recognised.  The  motion  of  tremors,  or  vibrations,  is  perceived 
by  several  senses,  but  especially  by  those  of  hearing  and  touch. 

Sensations  of  Chemical  Actions. — -We  are  made  acquainted 
with  chemical  actions  principally  by  taste,  smell,  and  touch,  and  by 
each  of  these  senses  in  the  mode  proper  to  it.  Volatile  bodies, 
disturbing  the  conditions  of  the  nerves  by  a  chemical  action,  exert 
the  greatest  influence  upon  the  organ  of  smell ;  and  many  matters 
act  on  that  sense  which  produce  no  impression  upon  the  organs  of 
taste  and  touch, — for  example,  many  odorous  substances,  as  the 
vapour  of  metals,  such  as  lead,  and  the  vapour  of  many  minerals. 
Some  volatile  substances,  however,  are  perceived  not  only  by  the 
sense  of  smell,  but  also  by  the  senses  of  touch  and  taste.  Thus, 
the  vapours  of  horse-radish  and  mustard,  and  acrid  suffocating 
gases,  act  upon  the  conjunctiva  and  the  mucous  membrane  of  the 
lungs,  exciting,  through  the  common  sensory  nerves,  merely  modi- 
fications of  common  feeling ;  and  at  the  same  time  they  excite  the 
ensations  of  smell  and  of  taste. 


chap,  xix.]  TOUCH,  65 r 


Special  Senses— Touch. 

Seat. — The  sense  of  touch  is  not  confined  to  particular 
parts  of  the  body  of  small  extent,  like  the  other  senses j  on 
the  contrary,  all  parts  capable  of  perceiving  the  presence  of  a 
stimulus  by  ordinary  sensation  are,  in  certain  degrees,  the  seat  of 
this  sense  ;  for  touch  is  simply  a  modification  or  exaltation  of 
common  sensation  or  sensibility.  The  nerves  on  which  the  sense 
of  touch  depends  are,  therefore,  the  same  as  those  which  confer 
ordinary  sensation  on  the  different  parts  of  the  body,  viz.,  those 
derived  from  the  posterior  roots  of  the  nerves  of  the  spinal  eord, 
and  the  sensory  cerebral  nerves. 

But,  although  all  parts  of  the  body  supplied  with  sensory  nerves 
are  thus,  in  some  degree,  organs  of  touch,  yet  the  sense  is  exer- 
eised  in  perfection  only  in  those  parts  the  sensibility  of  which  is 
extremely  delicate,  e.g.,  the  skin,  the  tongue,  and  the  lips,  which 
are  provided  with  abundant  papillae.  A  peculiar  and,  of  its  own 
kind  in  each  ease,  a  very  acute  sense  of  touch  is  exercised  through 
the  medium  of  the  nails  and  teeth.  To  a  less  extent  the  hair  may 
be  reckoned  an  organ  of  touch;  as  in  the  case  of  the  eyelashes. 
The  sense  of  touch  renders  us  conscious  of  the  presence  of  a 
stimulus,  from  the  slightest  to  the  most  intense  degree  of  its  action, 
by  that  indescribable  something  which  we  call  feeling,  or  common 
sensation.  The  modifications  of  this  sense  often  depend  on  the  ex- 
tent of  the  parts  affected.  The  sensation  of  pricking,  for  example, 
informs  us  that  the  sensitive  particles  are  intensely  affected 
in  a  small  extent ;  the  sensation  of  pressure  indicates  a  slighter 
affection  of  the  parts  in  the  greater  extent,  and  to  a  greater  depth. 
It  is  by  the  depth  to  which  the  parts  are  affected  that  the  feeling 
of  pressure  is  distinguished  from  that  of  mere  contact.  Schiff  and 
Brown-Sequard  are  of  opinion  that  common  sensibility  and  tactile 
sensibility  manifest  themselves  to  the  individual  by  the  aid  of 
different  sets  of  fibres.  Sievcking-  has  arrived  at  the  same  con- 
clusion from  pathological  observation. 

Varieties. — (a)  The  sense  of  touch,  strictly  so-called  (tactile 
sensibility),  (6)  the  sense  of  pressure,  (c)  the  sense  of  temperature. 
These  when  carried  beyond  a  certain  degree  are  merged  in  (d)  the 
sensation  of  pain. 


652  THE    SEXSES.  [chap.  xix. 

Various  peculiar  sensations,  such  as  tickling,  must  be  classed  with  pain 
under  the  head  of  common  sensations,  since  they  give  us  no  information  as 
to  external  objects.  Such  sensations,  whether  pleasurable  or  painful,  are  in 
all  cases  referred  by  the  mind  to  the  part  affected,  and  not  to  the  cause 
which  stimulates  the  sensory  nerves  of  the  part.  The  sensation  of  tickling 
may  be  produced  in  many  parts  of  the  body,  but  with  especial  intensity  in 
the  soles  of  the  feet.  Among  other  sensations  belonging  to  this  class,  and 
confined  to  particular  parts  of  the  body,  may  be  mentioned  those  of  the 
genital  organs  and  nipples. 

(a)  Touch  proper. — In  almost  all  parts  of  the  body  which 
have  delicate  tactile  sensibility  the  epidermis,  immediately  over 
the  papilla?,  is  moderately  thin.  "When  its  thickness  is  much  in- 
creased, as  over  the  heel,  the  sense  of  touch  is  very  much  dulled. 
On  the  other  hand,  when  it  is  altogether  removed,  and  the  cutis 
laid  bare,  the  sensation  of  contact  is  replaced  by  one  of  pain. 
Further,  in  all  highly  sensitive  parts,  the  papillae  arc  numerous 
and  highly  vascular,  and  usually  the  sensory  nerves  are  con- 
nected  with    special    End-organs,    such    as    have    been    described 

(P-  4I5)- 

The  acuteness  of  the  sense  of  touch  depends  very  largely  on  the 

cutaneous   circulation, .  which  is  of  course  largely  influenced   by 

external  temperature.      Hence  the  numbness,  familiar  to  everyone, 

produced  by  the  application  of  cold  to  the  skin. 

Special  organs  of  touch  are  present  in  most  animals,  among  which  may  be 
mentioned  the  antennae  of  insects,  the  '-whiskers''  (vibrissa)  of  cats  and 
other  carnivura.  the  wings  of  bats,  the  trunk  of  the  elephant,  and  the  hand 
of  man. 

Judgment  of  the  Form  and  Size  of  Bodies. — By  the 
sense  of  touch  the  mind  is  made  acquainted  with  the  size,  form, 
and  other  external  characters  of  bodies.  And  in  order  that  these 
characters  may  be  easily  ascertained,  the  sense  of  touch  is  especially 
developed  in  those  parts  which  can  be  readily  moved  over  the 
surface  of  bodies.  Touch,  in  its  more  limited  sense,  or  the  act  of 
examining  a  body  by  the  touch,  consists  merely  in  a  voluntary 
employment  of  this  sense  combined  with  movement,  and  stands  in 
the  same  relation  to  the  sense  of  touch,  or  common  sensibility, 
generally,  as  the  act  of  seeking,  following,  or  examining  odours, 
does  to  the  sense  of  smell.  The  hand  is  best  adapted  for  it,  by 
reason  of  its  peculiarities  of  structure, — namely,  its  capability  of 
pronation   and  supination,  which  enables  it,  by  the  movement   of 


<  hat.  xix.]  TOUCH,  653 

rotation,  to   examine  the  whole   circumference  of  the  body;  the 
power  it  pose  •'  opposing  the  thumb  to  the  rest  of  the  hand, 

and  the   relative    mobility  of  the  fingers  :   and  lastly   from  the 
abundance  of  the  sensory  terminal   organs  which  it  p  In 

forming  a  conception  of  the  figure  and  extent  of  a  surface,  the 
mind  multiplies  the  size  of  the  hand  or  fingers  used  in  the  inquiry 
by  the  number  of  times  which  it  is  contained  in  the  surface  tra- 
il :  and  by  repeating  this  process  with  regard  to  the  different 
dimensions  of  a  solid  body,  acquires  a  notion  of  its  cubical  extent. 
but,  of  course,  only  an  imperfect  notion,  as  other  senses,  e.g.,  the 
sight,  are  required  to  make  it  complete. 

Acuteness  of  Touch.— The  perfection  of  the  sense  of  touch 
on  different  parts  of  the  surface  is  proportioned  to  the  power  which 
such  parte  p —  -  of  distinguishing  and  isolating  the  sensations 
produced  by  two  points  placed  close  together.  This  power 
depends,  at  least  in  pan,  on  the  number  of  primitive  nerve-fibres 
distributed  to  the  part  ;  for  the  fewer  the  primitive  fibres  which  an 
organ  receives,  the  more  likely  is  it  that  several  impressions  on 
different  contiguous  points  will  act  on  only  one  nervous  fibre,  and 
hence  be  confounded,  and  perhaps  produce  but  one  sensation. 
Experiments  have  been  made  to  determine  the  tactile  pro- 
perties of  different  parts  of  the  skin,  as  measured  by  this  power 
of  distinguishing  distances.  These  consist  in  touching  the 
skin,  while  the  eyes  are  closed,  with  the  points  of  a  pair  of  coni- 
3  sheathed  with  cork,  and  in  ascertaining  how  close  the 
points  of  com]  >asses  might  be  brought  to  each  other,  and  still 
be    felt    as    two    bodies.       (E.    H.    Weber,    Valentin.) 


Table  of  variations  in  the  tactile  sensibility  of  different 
parts. — The  measurement  indicates  the  least  distance  at  which 

the  two  blunted  points  of  a  pair  of  compasses  could  he  separately 
distinguished.     (E.  H.  Weber.) 

Tip  of  tongue ^  inch 

Palmar  surface  of  third  phalanx  of  forefinger 

Palmar  surface  of  second  phalanges  of  fingers 

Red  surface  of  under-lip 

Tip  of  the  nose  ...... 


1 

1 2 

6  » 

6 

1 


654  TIIE    SENSES.  [chap.  xix. 

Middle  of  dorsum  of  tongue  .....  ~  inch. 

Palm  of  hand    .          .          .          .          .          .          .  A"  »» 

Centre  of  hard  palate    ......  -}  „ 

Dorsal  surface  of  first  phalanges  of  fingers  .          .  tt    m 

Back  of  hand         .          .          .          .          .          .     .  i-£  „ 

Dorsum  of  foot  near  toes   .         .         .         .         .  i-f-  „ 

Gluteal  region       .          .          .          .          .          .     .  i|  „ 

Sacral  region     .          .          .          .          .          .          .  i^  ,, 

Upper  and  lower  parts  of  forearm .          .          .  i-}  ,, 

Back  of  neck  near  occiput .          .          .          .          .  2  ,, 

Upper  dorsal  and  mid-lumbar  regions     .          .     .  2  ,, 

Middle  part  of  forearm       .         .         .         .  z\  „ 

Middle  of  thigh 2%  „ 

Mid-cervical  region    .          .         .         .         .  z.\  „ 

Mid-dorsal  region           .         .         .         .          .  2\  ,, 

Moreover,  in  the  case  of  the  limbs,  it  was  found  that  before  they 
were  recognised  as  two,  the  points  of  the  compasses  had  to  be 
farther  separated  when  the  line  joining  them  was  in  the  long  axis 
of  the  limb,  than  when  in  the  transverse  direction. 

According  to  Weber  the  mind  estimates  the  distance  between  two 
points  by  the  number  of  unexcited  nerve-endings  which  intervene 
between  the  two  points  touched.  It  would  appear  that  a  certain 
number  of  intervening  unexcited  nerve-endings  are  necessary 
before  two  points  touched  can  be  recognised  as  separate,  and  the 
greater  this  number  the  more  clearly  are  the  points  of  contact 
distinguished  as  separate.  By  practice  the  delicacy  of  a  sense  of 
touch  may  be  very  much  increased.  A  familiar  illustration  occurs 
in  the  case  of  the  blind,  who,  by  constant  practice,  can  acquire  the 
power  of  reading  raised  letters  the  forms  of  which  are  almost  if 
not  quite  undistinguishable,  by  the  sense  of  touch,  to  an  ordinary 
person. 

The  power  of  correctly  localising  sensations  of  touch  is  gradually 
derived  from  experience.  Thus  infants  when  in  pain  simply  cry, 
but  make  no  effort  to  remove  the  cause  of  irritation,  as  an  older 
child  or  adult  would,  doubtless  on  account  of  their  imperfect 
knowledge  of  its  exact  situation.  By  long  experience  this  power 
of  localisation  becomes  perfected,  till  at  length  the  brain  possesses 
a  complete  "  picture  "  as  it  were  of  the  surface  of  the  bodv,  and  is 


.  ii.vi-.  xix. J  TOUCH.  655 

able   with    marvellous   exactness   to    localise    each   sensation   of 

touch. 

Illusions  of  Touch. — The  different  degrees  of  sensitiveness 
issed  by  different  j»;irts  may  give  rise  to  errors  of  judgment  in 
estimating  the  distance  between  two  points  where  the  skin  is 
touched.  Thus,  if  blunted  points  of  a  pair  of  compasses  (main- 
tained at  a  constant  distance  apart)  he  slowly  drawn  over  the 
skin  of  the  cheek  towards  the  lips,  it  is  almost  impossible  to  resist 
the  conclusion  that  the  distance  between  the  points  is  gradually 
increasing.  When  they  reach  the  lips  they  seem  to  be  con- 
siderably further  apart  than  on  the  cheek.  Thus,  too,  our  esti- 
mate of  the  size  of  a  cavity  in  a  tooth  is  usually  exaggerated  when 
based  upon  sensation  derived  from  the  tongue  alone.  Another 
curious  illusion  may  here  be  mentioned.  If  we  close  the  eyes,  and 
place  a  small  marble  or  pea  between  the  crossed  fore  and  middle 
fingers,  we  seem  to  be  touching  two  marbles.  This  illusion  is  due 
tt>  an  error  of  judgment.  The  marble  is  touched  by  two  surfaces 
which,  under  ordinary  circumstances,  could  only  be  touched  by 
two  separate  marbles,  hence  the  mind,  taking  no  cognizance  of  the 
fact  that  the  fingers  are  crossed,  forms  the  conclusion  that  two 
sensations  are  due  to  two  marbles. 

(b)  Pressure. — It  is  extremely  difficult  to  separate  touch  proper 
from  sensations  of  pressure,  and,  indeed,  the  former  may  be  said 
to  depend  upon  the  latter.  If  the  hand  be  rested  on  the  table 
and  a  very  light  body  such  as  a  small  card  placed  on  it,  the  only 
sensation  produced  is  one  of  contact  ;  if,  however,  an  ounce  weight 
be  laid  on  the  card  an  additional  sensation  (that  of  pressure)  is 
experienced,  and  this  becomes  more  intense  as  the  weight  is  in- 
creased. If  now  the  weight  be  raised  by  the  hand,  we  are  con- 
scious of  overcoming  a  certain  resistance  ;  this  consciousness  is 
due  to  what  is  termed  the  "  imismlar  sense  "  (p.  599).  The  csti 
mate  of  a  weight  is,  therefore,  usually  based  on  two  sensations, 
(1)  of  pressure  on  the  skin,  and  (2)  the  muscular  sense. 

The  estimate  of  weight  derived  from  a  combination  of  these  two  sensa- 
tions (as  in  lifting  a  weight)  is  more  accurate  than  that  derived  from  the 
former  alone  (as  when  a  weight  is  laid  on  the  hand) ;  thus  "Weber  found 
that  by  the  former  method  he  could  generally  distinguish  19^  oz.  from  20  oz., 
but  not  19!  oz.  from  20  oz..  while  by  the  latter  he  could  at  most  only  dis- 
tinguish 14^  oz.  from  15  oz. 


656  THE    SENSES.  [chap.  xix. 

It  is  not  the  absolute,  but  the  relative,  amount  of  the  difference 
of  weight  which  we  have  thus  the  faculty  of  perceiving. 

It  is  not,  however,  certain,  that  our  idea  of  the  amount  of  muscular  force 
used  is  derived  solely  from  sensation  in  the  muscles.  We  have  the  power  of 
estimating  very  accurately  beforehand,  and  of  regulating,  the  amount  of 
nervous  influence  necessary  for  the  production  of  a  certain  degree  of  move- 
ment. "When  we  raise  a  vessel,  with  the  contents  of  which  we  are  not 
acquainted,  the  force  we  employ  is  determined  by  the  idea  we  have  con- 
ceived of  its  weight.  If  it  should  ha  ppen  to  contain  some  very  heavy  sub- 
stance, as  quicksilver,  we,  shall  probably  let  it  fall  ;  the  amount  of  muscular 
action,  or  of  nervous  energy,  which  we  had  exerted  being  insufficient.  The 
same  thing  occurs  sometimes  to  a  person  descending  stairs  in  the  dark  ;  he 
makes  the  movement  for  the  descent  of  a  step  which  does  not  exist.  It  is 
possible  that  in  the  same  way  the  idea  of  weight  and  pressure  in  raising 
bodies,  or  in  resisting  forces,  may  in  parr  arise  from  a  consciousness  of  the 
amount  of  nervous  energy  transmitted  from  the  brain  rather  than  from  a 
sensation  in  the  muscles  themselves.  The  mental  conviction  of  the  inability 
longer  to  support  a  weight  must  also  be  distinguished  from  the  actual  sensa- 
tion of  fatigue  in  the  muscles. 

So.  with  regard  to  the  ideas  derived  from  sensations  of  touch  combined 
with  movements,  it  is  doubtful  how  far  the  consciousness  of  the  extent  of 
muscular  movement  is  obtained  from  sensations  in  the  muscles  themselves. 
The  sensation  of  movement  attending  the  motions  of  the  hand  is  very  slight ; 
and  persons  who  do  not  know  that  the  action  of  particular  muscles  is 
necessary  for  the  production  of  given  movements,  do  not  suspect  that  the 
movement  of  the  fingers,  for  example,  depends  on  an  action  in  the  forearm. 
The  mind  has.  nevertheless,  a  very  definite  knowledge  of  the  changes  of 
position  produced  by  movements  ;  and  it  is  on  this  that  the  ideas  which  it 
conceives  of  the  extension  and  form  of  a  body  are  in  great  measure 
founded. 

(c)  Temperature. — The  whole  surface  of  the  body  is  more  or 
less  sensitive  to  differences  of  temperature.  The  sensation  of  heat 
is  distinct  from  that  of  touch;  and  it  would  seem  reasonable  to 
suppose  that  there  are  special  nerves  and  nerve-endings  for  tem- 
perature. At  any  rate  the  power  of  discriminating  temperature 
may  remain  unimpaired  when  the  sense  of  touch  is  temporarily  in 
abeyance.  Thus  if  the  ulnar  nerve  be  compressed  at  the  elbow 
till  the  sense  of  touch  is  very  much  dulled  in  the  fingers  which  it 
supplies,  the  sense  of  temperature  remains  quite  unaffected 
(Nothnagel). 

The  sensations  of  heat  and  cold  are  often  exceedingly  fallacious, 
and  in  many  cases  are  no  guide  at  all  to  the  absolute  temperature 
as  indicated  by  a  thermometer.  All  that  we  can  with  safety  infer 
from  our   sensations    of  temperature,  is    that  a  given   object   is 


.iiAi".  xix. J  SENSATION    OP  TEMPERATURE,  657 

warmer  or  cooler  than  the  skin.     Thua  the   temperature  of  our 

skin  is  the  standard  ;  and  as  this  varies  from  hour  to  hour  accord- 
ing to  the  activity  of  the  cutaneous  circulation,  our  estimate  of 
the  absolute  temperature  of  any  body  must  necessarily  vary  too. 
[f  we  put  the  left  hand  into  water  at  40  F.  and  the  right  into 
water  at  110  P.,  and  then  immerse  both  in  water  at  ,So  l\,  it 
will  feel  warm  to  the  left  hand  but  cool  to  the  right.  Again  a 
piece  of  metal  which  has  really  the  same  temperature  as  a  given 
piece  of  wood  will  feel  much  colder,  since  it  conducts  away  the 
heat  much  more  rapidly.  For  the  same  reason  air  in  motion 
feels  very  much  cooler  than  air  of  the  same  temperature  at  rest. 

Perhaps  the  most  striking  example  of  the  fallaciousness  of  our 
sensations  as  a  measure  of  temperature  is  afforded  by  fever.  In  a 
shivering  tit  of  ague  the  patient  feels  excessively  cold,  whereas  his 
actual  temperature  is  several  degrees  above  the  normal,  while  in 
the  sweating  stage  which  succeeds  it  he  feels  very  warm,  whereas 
really  his  temperature  has  fallen  several  degrees.  In  the  former 
case  the  cutaneous  circulation  is  much  diminished,  in  the  hitter 
much  increased  :  hence  the  sensations  of  cold  and  heat  respec- 
tively. 

In  some  cases  we  are  able  to  form  a  fairly  accurate  estimate  of 
absolute  temperature.  Thus,  by  plunging  the  elbow  into  a  bath, 
a  practised  bath-attendant  can  tell  the  temperature  sometimes 
within  i°  F. 

The  temperatures  which  can  be  readily  discriminated  are 
between  500 — 1150  F.  (io° — 450  C.) ;  very  low  and  very  high 
temperature  alike  produce  a  burning  sensation.  A  temperature 
appears  higher  according  to  the  extent  of  cutaneous  surface  ex- 
posed to  it.  Thus,  water  of  a  temperature  which  can  be  readily 
borne  by  the  hand,  is  epiite  intolerable  if  the  whole  body  be 
immersed.  So,  too,  water  appears  much  hotter  to  the  hand  than 
to  a  single  finger. 

The  delicacy  of  the  sense  of  temperature  coincides  in  the  main 
with  that  of  touch,  and  appears  to  depend  largely  on  the  thickness 
of  the  skin  ;  hence,  in  the  elbow  where  the  skin  is  thin,  the  sense 
of  temperature  is  delicate,  though  that  of  touch  is  not  remarkably 
so.  Weber  has  further  ascertained  the  following  facts :  two 
e<  anpass  points  so  near  together  on  the  skin  that  they  produce 
but  a  single  impression,  at  once  give  rise  to  two  sensations,  when 

.  u  u 


658  THE   SENSES.  [chap.  xix. 

one  is  hotter  than  the  other.     Moreover,  of  two  bodies  of  equal 
weight,  that  which  is  the  colder  feels  heavier  than  the  other. 

As  every  sensation  is  attended  with  an  idea,  and  leaves  behind 
it  an  idea  in  the  mind  which  can  be  reproduced  at  will,  we  are 
enabled  to  compare  the  idea  of  a  past  sensation  with  another 
sensation  really  present.  Thus  we  can  compare  the  weight  of  one 
body  with  another  which  we  had  previously  felt,  of  which  the  idea 
is  retained  in  our  mind.  "Weber  was  indeed  able  to  distinguish  in 
this  manner  between  temperatures,  experienced  one  after  the  other, 
better  than  between  temperatures  to  which  the  two  hands  were 
simultaneously  subjected.  This  power  of  comparing  present  with 
past  sensations  diminishes,  however,  in  proportion  to  the  time 
which  has  elapsed  between  them.  After-sensations  left  by  impres- 
sions on  nerves  of  common  sensibility  or  touch  are  very  vivid  and 
durable.  As  long  as  the  condition  into  which  the  stimulus  has 
thrown  the  organ  endures,  the  sensation  also  remains,  though  the 
exciting  cause  should  have  long  ceased  to  act.  Both  painful  and 
pleasurable  sensations  afford  many  examples  of  this  fact. 

Subjective  sensations,  or  sensations  dependent  on  internal 
causes,  are  in  no  sense  more  frequent  than  in  the  sense  of  touch. 
All  the  sensations  of  pleasure  and  pain,  of  heat  and  cold,  of  light- 
ness and  weight,  of  fatigue,  etc.,  may  be  produced  by  internal 
causes.  Neuralgic  pains,  the  sensation  of  rigor,  formication  or  the 
creeping  of  ants,  and  the  states  of  the  sexual  organs  occurring 
during  sleep,  afford  striking  examples  of  subjective  sensations. 
The  mind  has  a  remarkable  power  of  exciting  sensations  in  the 
nerves  of  common  sensibility  ;  just  as  the  thought  of  the  nauseous 
excites  sometimes  the  sensation  of  nausea,  so  the  idea  of  pain  gives 
rise  to  the  actual  sensation  of  pain  in  a  part  predisposed  to  it ; 
numerous  examples  of  this  influence  might  be  quoted. 

Taste. 

Conditions  necessary. — The  conditions  for  the  perceptions  of 
taste  are  : — 1,  the  presence  of  a  nerve  and  nerve-centre  with 
special  endowments ;  2,  the  excitation  of  the  nerve  by  the  sapid 
matters,  which  for  this  purpose  must  be  in  a  state  of  solution. 
The  nerves  concerned  in  the  production  of  the  sense  of  taste  have 
been  already  considered  (pp.  626  and  630).  The  mode  of  action  of 
the  substances  which  excite  taste  consists  in  the  production  of  a 


okap.xix.]  THE  SENSE  OF  TA8TE.  659 

change  in  the  condition  of  the  gustatory  nerves,  and  the  conduc- 
tionofthe  Btimulua  thus  produced  to  the  nerve-centre  ;  and,  ac 
ing  to  the  difference  of  the  substances,  an  infinite  variety  of  changes 
of  condition  of  the  nerves,  and  consequently  of  stimulations  of 

the  gustatory  centre,  may  be  induced.  The  mutters  to  be  tasted 
must  either  be  in  Bolution  or  be  soluble  in  the  moisture  covering 
the  tongue;  hence  insoluble  substances  are  usually  tasteless,  and 
produce  merely  sensations  of  touch.  Moreover,  for  the  perfect 
action  of  a  sapid,  as  of  an  odorous  substance,  it  is  necessary  that 
the  sentient  surface  should  be  moist.  Hence,  when  the  tongue 
and  fauces  are  dry,  sapid  substances,  even  in  solution,  are  with 
difficulty  tasted. 

The  nerves  of  taste,  like  the  nerves  of  other  special  senses,  may  have  their 
peculiar  properties  excited  by  various  other  kinds  of  irritation,  such  as 
electricity  and  mechanical  impressions.  Thus,  Henle  observed  that  a  small 
current  of  air  directed  upon  the  tongue  gives  rise  to  a  cool  saline  taste,  like 
that  of  saltpetre  ;  and  Baly  has  shown  that  a  distinct  sensation  of  taste, 
similar  to  that  caused  by  electricity,  may  be. produced  by  a  smart  tap  applied 
to  the  papillae  of  the  tongue.  Moreover,  the  mechanical  irritation  of  the 
fauces  and  palate  produces  the  sensation  of  nausea,  which  is  probably  only 
a  modification  of  taste. 

Seat  of  sensation. — The  principal  seat  of  the  sense  of  taste  is 
the  tongue.  But  the  results  of  experiments  as  well  as  ordinary 
experience  show  that  the  soft  palate  and  its  arches,  the  uvula, 
tonsils,  and  probably  the  upper  part  of  the  pharynx,  are  endowed 
with  taste.  These  parts,  together  with  the  base  and  posterior 
parts  of  the  tongue,  are  supplied  with  branches  of  the  glosso- 
pharyngeal nerve,  and  evidence  has  been  already  adduced  that  the 
sense  of  taste  is  conferred  upon  them  by  this  nerve.  In  most, 
though  not  in  all  persons,  the  anterior  parts  of  the  tongne, 
especially  the  edges  and  tip,  are  endowed  with  the  sense  of  taste. 
The  middle  of  the  dorsum  is  only  feebly  endowed  with  this  sense, 
probably  because  of  the  density  and  thickness  of  the  epithelium 
covering  the  filiform  papilla  of  this  part  of  the  tongue,  which  will 
prevent  the  sapid  substances  from  penetrating  to  their  sensitive 
parts.  The  gustatory  property  of  the  anterior  part  of  the  tongue 
is  due,  as  already  said  (p.  626),  to  the  lingual  or  gustatory  branch 
of  the  fifth  nerve. 

Structure  of  the  Tongue.— The  tongue  is  a  muscular  organ 
covered   by  mucous   membrane.     The   muscles,  which  form  the 

U  U  2 


66o 


THE   SENSES. 


[chap.  xix. 


greater  part  of  the  substance  of  the  tongue  (intrinsic  muscles)  are 
termed  lingvales;  and  by  these.,  which  are  attached  to  the  mucous 


Kg.349._P«j«Bflr  turface  of  the  Umgue^tmih  the  fa«c*   ™fj<^ -*'.1'  Std 

TianiU^  ui  front  of  2,  the  foramen  etecum;  3,  fungiform  papulae  ,  4.  nWorm  ana 
eonkaf  nSill™  <  transverse  and  oblique  rug*  ;  6,  mucous  glands  at  the  base  of  the 
toSSe  and  inthe  fauces  ■  7.  tonsils  ;  8,  part  of  the  epiglottis  ;  9,  median  glosso^piglot- 
tidean  f old  :freenum  epiglottidis].     (From  Bappey.J 


membrane  chiefly,  its  smaller  and  more  delicate  movements  are 
chiefly  performed. 

By"  other  muscles  (extrinsic  muscles)  as  the  genio-hyoglossus, 


chap,  xix.]  THE  TONGUF.  66 1 

tin'  styloglossus,  etc^the  tongue  is  fixed  to  surrounding  parts;  and 
by  tliis  group  of  muecles  its  Larger  movements  are  performed* 

Tin'  mucous  membrane  of  tin'  tongue  resembles  other  mucous 
membranes  (p.  397)  in  essential  points  of  structure,  t >  1 1  r  contains 
papUlce,  more  or  less  peculiar  to  itself;  peculiar,  however,  in 
details  of  structure  and  arrangement,  not  in  their  nature.  The 
tongue  is  beset  with  numerous  mucous  follicles  ami  glands.  The 
f  the  tongue  in  relation  to  niastieation  and  deglutition  has 
already  been  considered  (]>]>.  27S  and  294). 

The  Larger  papillae  of  the  tongue  are  thickly  set  over  the 
anterior  two-thirds  of  its  upper  surface,  or  dorsum  (tig.  349),  and 
give  to  it  its  characteristic  roughness.  In  carnivorous  animals, 
especially  those  of  the  cat  tribe,  the  papilla?  attain  a  large  size, 
and  are  developed  into  sharp  recurved  horny  spines.  Such  papilke 
cannot  be  regarded  as  sensitive,  but  they  enable  the  tongue  to 
play  the  part  of  a  most  efficient  rasp,  as  in  scraping  bones,  or  of  a 
comb  in  cleaning  their  fur.  Their  greater  prominence  than  those 
of  the  skin  is  due  to  their  interspaces  not  being  filled  up  with 
epithelium,  as  the  interspaces  of  the  papilla?  of  the  skin  are.  The 
papillae  of  the  tongue  present  several  diversities  of  form;  but 
three  principal  varieties,  differing  both  in  seat  and  general 
characters,  may  usually  be  distinguished,  namely,  the  (1)  circv.m- 
vallate,  the  (2)  fun< giform,  and  the  (3)  filiform  papillae.  Essentially 
these  have  all  of  them  the  same  structure,  that  is  to  say,  they  are 
all  formed  by  a  projection  of  the  mucous  membrane,  and  contain 
special  branches  of  blood-vessels  and  nerves.  In  details  of  struc- 
ture, however,  they  differ  considerably  one  from  another. 

The  surface  of  each  kind  is  studded  by  minute  conical  processes 
of  mucous  membrane,  which  thus  form  secondary  papillae. 

Simple  papilla?  also  occur  over  most  other  parts  of  the  tongue  net 
occupied  by  the  compound  papilla?,  and  extend  for  some  distance  behind  the 
papilla?  circumvallatre.  The  mucous  membrane  immediately  in  front  of  the 
epiglottis  is.  however,  free  from  them.  They  are  commonly  buried  beneath 
the  epithelium  ;  hence  they  are  often  overlooked. 

(1.)  CircumvaUate. — These  papilla}  (fig.  350),  eight  or  ten  in 
number,  are  situate  in  two  V-shaped  lines  at  the  base  of  the 
tongue  (1,  1,  fig.  349)-  They  are  circular  elevations  from  ^jth  to 
TVth  of  an  inch  wide,  each  with  a  central  depression,  and  sur- 
rounded by  a  circular  fissure,  at  the  outside  of  which  again  is  a 


662 


THE  SENSES. 


[CHAP.  XIX. 


slightly  elevated  ring,  both  the   central  eLevation  and  the  ring- 
being  formed  of  close  set  simple  papillae  (fig.  350). 


Pig.  350. — Vertical  section  of  a  circumvallate  papilla  *£. — A,  the  papillae  ;  B,  the  surrounding 
■wall;  a,  the  epithelial  covering;  b,  the  nerves  of  the  papilla  and  -wall  spreading 
towards  the  surface ;  c,  the  secondary  papilhe.     (Kolliker.) 

(2.)  Fungiform. — The  fungiform  papilla?  (3,  fig.  349)  are  scat- 
tered chiefly  over  the  sides  and  tip,  and  sparingly  over  the  middle 
of  the  dorsum,  of  the  tongue ;  their   name  is  derived  from  their 


Fig.  351. — Surface  and  section  of  the  fungiform  papilla.  A,  the  surface  of  a  fungiform 
papilla,  partially  denuded  of  its  epithelium  ;  p,  secondary  papillae  ;  e,  epithelium.  B, 
section  of  a  fungiform  papilla  with  the  blood-vessels  injected;  a,  artery;  v,  vein; 
c,  capillary  loops  of  similar  papilla  in  the  neighbouring  structure  of  the  tongue ;  d, 
capillary  loops  of  the  secondary  papillte  ;  e,  epithelium.  (From  Kolliker,  after  Todd 
and  Bowman.) 

being  usually  narrower  at  their  base  than  at  their  summit.  They 
also  consist  of  groups  of  simple  papillae  (A.  fig.  351),  each  of  which 
contains  in  its  interior  a  loop  of  capillary  blood-vessels  (B.),  and  a 
nerve-fibre. 

(3.)  Conical  or  Filiform. — These,  which  are  the  most  abundant 
papillae,  are  scattered  over  the  whole  surface  of  the  tongue,  but 
especially  over  the  middle  of  the  dorsum  (fig.  349).  They  vary 
in  shape  somewhat,  but  for  the  most  part  are  conical  or  filiform, 


(ll  LP.   \i.\.  | 


PAPILLJ  . 


663 


and  covered  by  a  thick  layer  of  epidermis,  which  is  arranged  over 
them,  either  in  an  imbricated  manner,  or  is  prolonged  from  their 
surface  in  the  form  of  fine  stiff  projections,  hair-like  in  appearan 
and  in  Borne  instances  in 
structure  also  (fig.  352 ). 
From       their       peculiar 
structure,  it  seems  likely 

that    these    papillae    have 

a    mechanical    function, 

or  one  allied  to  that  of 
touch  rather  than  of 
taste  ;  the  latter  sense 
being  probably  seated 
especially  in  the  other 
two  varieties  of  papilla1, 
the  circumvallate  and  the 
fungiform. 

The  epithelium  of  the 
tongue  is  stratified  with 
the  upper  layers  of  the 
squamous  kind.  It  co- 
vers every  part  of  the 
surface ;  but  over  the 
fungiform  papillae  forms 
a  thinner  layer  than 
elsewhere.  The  epithe- 
lium covering  the  filiform 
papillae  is  extremely 
dense  and  thick,  and,  as 
1  >efore  mentioned,  pro- 
jects from  their  sides 
and  summits  in  the  form 
of    long,    stiff,    hair-like 

processes  (tig.  352).  Many  of  these  processes  bear  a  close  resem- 
blance to  hairs.  Blood-vessels  and  nerves  are  supplied  freely  to 
the  papilla.  The  nerves  in  the  fungiform  and  circumvallate 
papillae  form  a  kind  of  plexns,  spreading  out  brush-wise  (fig.  350), 
but  the  exact  mode  of  termination  of  the  nerve-filaments  is  not 
certainly  known. 


Fig1.  352.—  Two  fill  form  paptllcB,  one  with  epithelium, 
the  other -without.  V.— /'»  the  substance  of  the 
papillae  dividing  at  their  upper  extremities  into 
secondary  papillae  ;  a,  artery,  and  v,  vein,  dividing 
into  capillary  loops  ;  e,  epithelial  covering,  Lami- 
nated between  the  papiihe,  but  extended  into 
hair-like  processes,/,  from  the  extremities  of  the 
secondary  papilla?.  (From  Kiilliker,  after  Todd 
and  Bowman.) 


664 


THE   SENSES 


[CHAP.   XIX 


Taste  goblets. — Tn  the  eircumvallate  papillae  of  the  tongue  of  man. 
peculiar  structures  known  as  gustatory  buds  or  taste  goblets,  have 
been  discovered  (Loven,  Selnvalbe).  They  are  of  an  oval  Bhape, 
and  consist  vf  a  number  of  closely  packed,  very  narrow  and  fusi- 
form, cells  (gustatory  celts).     This  central  core  of  gustatory  cells  is 


1?ig.  $53.— Taste-gobUt  from  dog's  epiglottis  [laryngeal  surface  near  the  base),  precisely 
similar  in  struct ure  to  those  found  in  the  tongue,  a,  depression  in  epithelium  over 
goblet  :  below  the  letter  are  seen  the  tine  hair-like  processes  in  which  the  cells  termi- 
nate :  <-.  two  nuclei  of  the  axial  (gustatory  cells.  The  more  superficial  nuclei  belong- 
to  the  superficial  [encasing)  cells:  the  converging  lines  indicate  the  fusiform  shape  of 
the  encasing  cells.     X  400.     vSchofield.) 

enclosed  in  a  single  layer  of  broader  fusiform  cells  (encasing  cells). 
The  gustatory  colls  terminate  in  tine  spikes  not  unlike  cilia,  which, 
project  on  the  free  surface  (tig.  353). 

These  bodies  also  occur  side  by  side  in  considerable  numbers 
in  the  epithelium  of  the  papilla  foliata,  which  is  situated  near  the 
root  of  the  tongue  in  the  rabbit,  and  also  in  man.  Similar  "taste- 
goblets"  also  occur  pretty  evenly  distributed  on  the  posterior 
(laryngeal)  surface  of  the  epiglottis  (Verson,  Schofield).  It  seems 
probable,  from  their  distribution,  that  all  these  so-called  taste- 
goblets  are  gustatory  in  function,  though  no  nerves  have  been 
distinctly  traced  into  them. 

Other  Functions  of  the  Tongue. — Besides  the  sense  of 
taste,  the  tongue,  by  means  also  of  its  papillae,  is  endued;  (2) 
especially  at  its  sides  and  tip,  with  a  very  delicate  and  accu- 
rate sense  of  touch  (p.  653),  which  renders  it  sensible  of  the 
impressions  of  heat  and  cold,  pain  and  mechanical  pressure, 
and  consequently  of  the  form  of  surfaces.  The  tongue  may  lose 
its  common  sensibility,  and  still  retain  the  sense  of  taste,  and 
vice       rsd.       This    fact   renders   it    probable    that,    although    the 


ohap.xix.]  FUNCTIONS  OF  THE  TONG1  r.  66$ 

Benses  «»t'  taste  and  of  touch  may  be  exercised  by  the  same  papillae 
Bupplied  i-\  the  same  aerves,  ye1  the  nervous  conductors  for  these 
two  different  sensations  are  distinct,  just  as  the  aerves  for  smell 
and  common  sensibility  in  the  nostrils  are  distincl  ;  and  it  is  quite 
conceivable  that  the  same  nervous  trunk  may  contain  fibres  differ- 
ing essentially  in  their  specific  properties.  Pacts  already  detailed 
(p.  626)  seem  to  prove  that  the  Lingual  branch  of  the  fifth  nerve 
is  tlu>  conductor  of  sensations  of  taste  in  the  anterior  part  of  the 
tongue  ;  and  it  is  also  certain,  from  the  marked  manifestations  of 
pain  to  which  its  division  in  animals  gives  rise,  that  it  is  likewise  a 
nerve  of  common  sensibility.  The  glosso-pharyngeal  also  seems  to 
contain  fibres  both  of  common  sensation  and  of  the  special  sense 
of  taste. 

The  functions  of  the  tongue  in  connection  with  (3)  speech,  (4) 
mastication,  (5)  deglutition,  (6)  suction,  have  been  referred  to  in 
other  chapters* 

Taste  and  Smell ;  Perceptions. — The  concurrence  of  common 
and  special  sensibility  in  the  same  part  makes  it  sometimes  diffi- 
cult to  determine  whether  the  impression  produced  by  a  substance 
is  perceived  through  the  ordinary  sensitive  fibres,  or  through  those 
of  the  sense  of  taste.  In  many  cases,  indeed,  it  is  probable  that 
both  sets  of  nerve-fibres  are  concerned,  as  when  irritating  acrid 
substances  are  introduced  into  the  mouth. 

Much  of  the  perfection  of  the  sense  of  taste  is  often  due  to  the 
sapid  substances  being  also  odorous,  and  exciting  the  simultaneous 
action  of  the  sense  of  smell.  This  is  shown  by  the  imperfection 
of  the  taste  of  such  substances  when  their  action  on  the  olfactory 
nerves  is  prevented  by  closing  the  nostrils.  Many  fine  wines  lose 
much  of  their  apparent  excellence  if  the  nostrils  are  held  close 
while  they  are  drunk. 

Varieties  of  Tastes. — Among  the  most  clearly  defined  tastes 
are  the  sweet  and  bitter  (which  are  more  or  less  opposed  to  each 
other),  the  acid,  alkaline,  and  saline  tastes.  Acid  and  alkaline 
taste  may  be  excited  by  electricity.  If  a  piece  of  zinc  be  placed 
beneath  and  a  piece  of  copper  above  the  tongue,  and  their  ends 
brought  into  contact,  an  acid  taste  (due  to  the  feeble  galvanic 
current)  is  produced.  The  delicacy  of  the  sense  of  taste  is  suffi- 
cient to  discern  1  part  of  sulphuric  acid  in  1000  of  water ;  but  it 
is  far  surpassed  in  aeuteness  by  the  sense  of  smell. 


666  THE   SEXSES.  [chap.  xix. 

After-tastes. — Very  distinct  sensations  of  taste  are  frequently 
left  after  the  substances  which  excited  them  have  ceased  to  act 
on  the  nerve ;  and  such  sensations  often  endure  for  a  long 
time,  and  modify  the  taste  of  other  substances  applied  to  the 
tongue  afterwards.  Thus,  the  taste  of  sweet  substances  spoils 
the  flavour  of  wine,  the  taste  of  cheese  improves  it.  There 
appears,  therefore,  to  exist  the  same  relation  between  tastes  as 
between  colours,  of  which  those  that  are  opposed  or  comple- 
mentary render  each  other  more  vivid,  though  no  general  prin- 
ciples governing  this  relation  have  been  discovered  in  the  case  of 
tastes.  In  the  art  of  cooking,  however,  attention  has  at  all  times 
been  paid  to  the  consonance  or  harmony  of  flavours  in  their  com- 
bination or  order  of  succession,  just  as  in  painting  and  music  the 
fundamental  principles  of  harmony  have  been  employed  empiri- 
cally while  the  theoretical  laws  were  unknown. 

Frequent  and  continued  repetitions  of  the  same  taste  render 
the  perception  of  it  less  and  less  distinct,  in  the  same  way  that  a 
colour  becomes  more  and  more  dull  and  indistinct  the  longer  the 
eye  is"  fixed  upon  it.  Thus,  after  frequently  tasting  first  one  and 
then  the  other  of  two  kinds  of  wine,  it  becomes  impossible  to  dis- 
criminate between  them. 

The  simple  contact  of  a  sapid  substance  with  the  surface  of 
the  gustatory  organ  seldom  gives  rise  to  a  distinct  sensation  of 
taste  ;  it  needs  to  be  diffused  over  the  surface,  and  brought  into 
intimate  contact  with  the  sensitive  parts  by  compression,  friction, 
and  motion  between  the  tongue  and  palate. 

Subjective  Sensations  of  Taste. — The  sense  of  taste  seems 
capable  of  being  excited  only  by  external  causes,  such  as  changes 
in  the  conditions  of  the  nerves  or  nerve-centres,  produced  by  con- 
gestion or  other  causes,  which  excite  subjective  sensations  in  the 
other  organs  of  sense.  But  little  is  known  of  the  subjective 
sensations  of  taste  ;  for  it  is  difficult  to  distinguish  the  phenomena 
from  the  effects  of  external  causes,  such  as  changes  in  the  nature 
of  the  secretions  of  the  mouth. 

Smell. 

Conditions  necessary. — (i.)  The  first  conditions  essential 
to  the  sense  of  smell  are  a  special  nerve  and  nerve-centre,  the 
changes  in  whose  condition  are  perceived  in  sensations  of  odour ; 


CHAP,  xix.]  SENSE   OF   SMELL.  667 

ini'  no  other  nervous  structure  is  capable  of  these  sensations,  even 
though  acted  on  by  the  same  causes.     The  same  substance  which 

excites  the  sensation  of  smell  in  the  olfactory  centre  may  cause 
another  peculiar  sensation  through  the  nerves  of*  taste,  and  may 
produce  an  irritating  and  burning  sensation  on  the  nerves  of 
touch  ;  hut  the  sensation  of  odour  is  yet  separate  and  distinct 
from  these,  though  it  may  be  simultaneously  perceived.  (2.)  The 
second  condition  of  smell  is  a  peculiar  change  produced  in  the 
olfactory  nerve  and  its  centre  by  the  stimulus-  or  odorous  sub- 
stance. (3.)  The  material  causes  of  odours  are,  usually,  in  the 
case  of  animals  living  in  the  air,  either  solids  suspended  in  a  state 
of  extremely  fine  division  in  the  atmosphere ;  or  gaseous  exhala- 
tions often  of  so  subtile  a  nature  that  they  can  be  detected  by  no 
other  re-agent  than  the  sense  of  smell  itself.  The  matters  of 
odour  must,  in  all  cases,  be  dissolved  in  the  mucus  of  the  mucous 
membrane  before  they  can  be  immediately  applied  to,  or  affect 
the  olfactory  nerves  ;  therefore  a  further  condition  necessary  for 
the  perception  of  odours  is,  that  the  mucous  membrane  of  the 
nasal  cavity  be  moist.  When  the  Schneiderian  membrane  is  dry, 
the  sense  of  smell  is  impaired  or  lost ;  in  the  first  stage  of 
catarrh,  when  the  secretion  of  mucus  within  the  nostrils  is  less- 
ened, the  faculty  of  perceiving  odour  is  either  lost,  or  rendered 
very  imperfect.  (4.)  In  animals  living  in  the  air,  it  is  also  requi- 
site that  the  odorous  matter  should  be  transmitted  in  a  current 
through  the  nostrils.  This  is  effected  by  an  inspiratory  move- 
ment, the  mouth  being  closed ;  hence  we  have  voluntary  influence 
over  the  sense  of  smell ;  for  by  interrupting  respiration  we  prevent 
the  perception  of  odours,  and  by  repeated  quick  inspiration, 
assisted,  as  in  the  act  of  sniffing,  by  the  action  of  the  nostrils,  we 
render  the  impression  more  intense  (see  p.  248).  An  odorous  sub- 
stance in  a  liquid  form  injected  into  the  nostrils  appears  incapable 
of  giving  rise  to  the  sensation  of  smell :  thus  Weber  could  not 
smell  the  slightest  odour  when  his  nostrils  were  completely  filled 
with  water  containing  a  large  quantity  of  eau  de  Cologne. 

Seat  of  the  Sense  of  Smell. — The  human  organ  of  smell  is 
formed  by  the  filaments  of  the  olfactory  nerves,  distributed  in  the 
mucous  membrane  covering  the  upper  third  of  the  septum  of  the 
nose,  the  superior  turbinated  or  spongy  bone,  the  upper  part  of 
the  middle  turbinated  bone,  and  the  upper  wall  of  the  nasal  cavities 


668  THE   SENSES.  [chap.  xix. 

beneath  the  cribriform  plates  of  the  ethmoid  bones  (figs.  354  and 
355).  The  olfactory  region  is  covered  by  cells  of  cylindrical  epi- 
thelium, prolonged  at  their   deep   extremities   into  fine  branched 


XII 


Fig.  354. — Naves  of  the  septum  nasi,  seen  from  the  right  side.  f. — I.  the  olfactory  bulb  ;  i, 
the  olfactory  nerves  passing  through  the  foramina  of  the  cribriform  plate,  and  de- 
scending to  be  distributed  on  the  septum  ;  2,  the  internal  or  septal  twig  of  the  nasal 
branch  of  the  ophthalmic  nerve ;  3,  naso-palatine  nerves.  (From  Sappey,  after  Hirsch- 
feld  and  Leveille.) 

processes,  but  not  ciliated ;  and  interspersed  with  these  are  fusi- 
form (olfactory)  cells,  with  both  superficial  and  deep  processes  (fig. 
356),  the  latter  being  probably  connected  with  the  terminal  fila- 
ments of  the  olfactory  nerve.  The  lower,  or  respiratory  part,  as 
it  is  called,  of  the  nasal  fossae  is  lined  by  cylindrical  ciliated  epi- 
thelium, except  in  the  region  of  the  nostrils,  where  it  is  squamous. 
The  branches  of  the  olfactory  nerves  retain  much  of  the  same  soft 
and  greyish  texture  which  distinguishes  those  of  the  olfactory 
j/racts  within  the  cranium.  Their  filaments,  also,  are  peculiar, 
more  resembling  those  of  the  sympathetic  nerve  than  the  filaments 
of  the  other  cerebral  nerves  do,  containing  no  outer  white  sub- 
stance, and  being  finely  granular  and  nucleated.  The  sense  of 
smell  is  derived  exclusively  through  those  parts  of  the  nasal 
cavities  in  which  the  olfactory  nerves  are  distributed  ;  the  acces- 
sory cavities  or  sinuses  communicating  with  the  nostrils  seem  to 
have  no  relation  to  it.  Air  impregnated  with  the  vapour  of  cam- 
phor was  injected  into  the  frontal  sinus  through  a  fistulous  opening, 
and  odorous  substances  have  been  injected  into  the  antrum  of 
Highmore  ;  but  in  neither  case  was   any  odour  perceived  by  the 


CHAP.  XIX.  1 


c>K<;.\.\   of   SMELL. 


669 


patient.     The  purposes  of  these  sinuses  appear  to  be,  that  the 
bones,   necessarily  Large  for  the  action  of  the  muscles  and  other 
parts  connected  with  them,  may  lie  as  light  as  possible,  and  thai 
there  may  be  more  room  for 
the    resonance   of  the   air  in 
vocalising.     The  former  pur- 
pose, which  is  in  other  bones 
obtained  by  Oiling  their  cavi- 
ties with  fat,  is  here  attained, 
as  it  is  in  many  bones  of  birds, 
by  their  being  rilled  with  air. 

Other  Functions  of  the 
Olfactory  Region.  —  All 
parts  of  the  nasal  cavities, 
whether  or  not  they  can  be 
the  seats  of  the  sense  of  smell, 
are  endowed  with  common  sen- 
sibility by  the  nasal  branches 
of  the  first  and  second  divi- 
sions of  the  fifth  nerve.  Hence 
the  sensations  of  cold,  heat, 
itching,  tickling,  and  pain  ■ 
and  the  sensation  of  tension 
or  pressure  in  the  nostrils. 
That  these  nerves  cannot  per- 
form the  function  of  the  olfac- 
tory nerves  is  proved  by  cases 


Fig.  355. — Nerves  of  the  outer  walls  of  the  nasal 
fossce.  £ .— 1,  network  of  the  branches  of 
the  olfactory  nerve,  descending  upon  the 
region  of  the  superior  and  middle  turbi- 
nated bones ;  2,  external  twig  of  the  eth- 
moidal branch  of  the  nasal  nerves ;  3, 
spheno-palatine  ganglion  ;  4,  ramification 
of  the  anterior  palatine  nerves  ;  5,  poste- 
rior, and  6,  middle  divisions  of  the  palatine 
nerves  ;  7,  branch  to  the  region  of  the  in- 
ferior turbinated  bone ;  8,  branch  to  the 
region  of  the  superior  and  middle  turbi- 
nated bones  ;  9,  naso-palatine  branch  to 
the  septum  cut  short.  (From  Sappey,  after 
Hirschfeld  and  Leveille.) 


in  which  the  sense  of  smell  is 

lost,  while  the  mucous  membrane  of  the  nose  remains  susceptible 
of  the  various  modifications  of  common  sensation  or  touch.  But 
it  is  often  difficult  to  distinguish  the  sensation  of  smell  from  that 
of  mere  feeling,  and  to  ascertain  what  belongs  to  each  separately. 
This  is  the  case  particularly  with  the  sensations  excited  in  the  nose 
by  acrid  vapours,  as  of  ammonia,  horse-radish,  mustard,  etc.,  which 
resemble  much  the  sensations  of  the  nerves  of  touch  ;  and  the 
difficulty  is  the  greater,  when  it  is  remembered  that  these  acrid 
vapours  have  nearly  the  same  action  upon  the  mucous  membrane 
of  the  eyelids.  It  was  because  the  common  sensibility  of  the  nose 
to  these  irritating  substances  remained  after  the  destruction  of 


670 


THE   SENSES. 


CHAP.   XIX. 


the    olfactory  nerves,   that  Magendie  was   led  to  the  erroneous 
belief  that  the  fifth  nerve  might  exercise  this  special  sense. 

Varieties    of    Odorous    Sensations. — Animals    do    not    all 
equally  perceive  the  same  odours ;  the  odours  most  plainly  per- 
ceived by  an  herbivorous  animal  and  by  a  carni- 
vorous  animal   are    different.       The    Carnivora 
have  the  power  of  .detecting  most  accurately  by 
the    smell   the    special   peculiarities    of   animal 
matters,  and  of  tracking  other  animals  by  the 
scent ;  but  have  apparently  very  little  sensibility 
to  the  odours  of  plants  and  flowers.   Herbivorous 
animals  are  peculiarly  sensitive  to  the  latter, 
and  have  a  narrower  sensibility  to  animal  odours, 
especially  to  such  as  proceed  from  other  indivi- 
duals than  their  own  species.    Man  is  far  inferior 
to  many  animals  of  both  classes  in  respect  of  the 
acuteness  of  smell ;  but  his  sphere  of  susceptibi- 
lity  to   various    odours    is   more   uniform    and 
extended.     The  cause  of  this  difference  lies  pro- 
bably in  the  endowments  of  the  cerebral  parts 
of  the  olfactory  apparatus.     The  delicacy  of  the 
sense  of  smell  is  most  remarkable  ;  it  can  dis- 
cern  the   presence    of  bodies    in  quantities   so 
minute  as  to  be  undiscoverable  even  by  spectrum 
analysis ;   lc>o,ooo,ooo  °f  a   grain   of  musk    can   be 
distinctly  smelt    (Valentin).       Opposed   to   the 
sensation  of   an  agreeable  odour  is  that  of  a 
disagreeable   or  disgusting  odour,   which   corre- 
sponds   to    the   sensations    of  pain,   dazzling   and  disharmony   of 
colours,  and  dissonance  in  the  other  senses.     The  cause  of  this 
difference  in  the   effect  of  different  odours  is  unknown :  but  this 
much  is  certain,  that  odours  are  pleasant  or  offensive  in  a  relative 
sense  only,  for  many  animals  pass  their   existence  in  the  midst  of 
odours  which  to  us  are  highly  disagreeable.     A  great  difference  in 
this   respect   is,   indeed,   observed  amongst  men :    many  odours, 
generally  thought  agreeable,  are  to  some  persons  intolerable;  and 
different   persons   describe    differently   the    sensations  that   they 
severally  derive  from  the  same  odorous  substances.     There  seems 
also  to  be  in  some  persons  an  insensibility  to  certain  odours,  corn- 


Fig.  356.—  Epithelial 
and  olfactory  cells 
of  man.  The  let- 
ters are  placed  on 
the  free  surface. 
E,  E,  epithelial 
cells;  Olf.,  olfac- 
tory cells.  (Max 
Schultze.) 


chap,  six.]  ODOBOUS  SENSATION.  671 

parable  with  that  of  the  eye  to  certain  colours;  and  among 
different  persons,  as  great  a  difference  in  the  acuteness  of  the  sense 
of  smell  as  among  others  in  the  acuteness  of  sight.  We  have  no 
exact  proof  that  a  relation  of  harmony  and  disharmony  exists 
between  odours  as  between  colours  and  sounds;  though  it  is  pro- 
bable that  such  is  the  ease,  since  it  certainly  is  so  with  regard  to 
the  sense  of  taste;  and  since  snch  a  relation  would  account  in 
some  measure  for  the  different  degrees  of  perceptive  power  in 
different  "persons  \  for  as  some  have  no  ear  for  music  (as  it  is 
said),  so  others  have  no  clear  appreciation  of  the  relation  of  odours, 
and  therefore  little  pleasure  in  them. 

Subjective  Sensations  of  Smell. — The  sensations  of  the 
olfactory  nerves,  independent  of  the  external  application  of  odorous 
substances,  have  hitherto  been  little  studied.  The  friction  of  the 
electric  machine  produces  a  smell  like  that  of  phosphorus.  Patter, 
too,  has  observed,  that  wrhen  galvanism  is  applied  to  the  organ  of 
smell,  besides  the  impulse  to  sneeze,  and  the  tickling  sensation 
excited  in  the  filaments  of  the  fifth  nerve,  a  smell  like  that  of 
ammonia  was  excited  by  the  negative  pole,  and  an  acid  odour  by 
the  positive  pole ;  whichever  of  these  sensations  were  produced,  it 
remained  constant  as  long  as  the  circle  was  closed,  and  changed  to 
the  other  at  the  moment  of  the  circle  being  opened.  Subjective 
sensations  occur  frequently  in  connection  with  the  sense  of  smell. 
Frequently  a  person  smells  something  which  is  not  present,  and 
which  other  persons  cannot  smell ;  this  is  very  frequent  with 
nervous  people,  but  it  occasionally  happens  to  every  one.  In  a 
man  who  was  constantly  conscious  of  a  bad  odour,  the  arachnoid 
was  found  after  death  to  be  beset  with  deposits  of  bone ;  and  in 
the  middle  of  the  cerebral  hemispheres  were  scrofulous  cysts  in  a 
state  of  suppuration.  Dubois  was  acquainted  with  a  man  who, 
ever  after  a  fall  from  his  horse,  which  occurred  several  years  before 
his  death,  believed  that  he  smelt  a  bad  odour. 

Hearing. 

Anatomy  of  the  Ear. — For  descriptive  purposes,  the  Ear,  or 
Organ  of  Hearing,  is  divided  into  three  parts,  (1)  the  external,  (2) 
the  middle,  and  (3)  the  internal  ear.  The  two  first  are  only  acces- 
sory to  the  third  or  internal  ear,  which  contains  the  essential  parts 


672 


THE   SENSES. 


[CHAP.  XIX. 


of  an  organ  of  hearing.     The  accompanying  figure  shows  very  Avell 
the  relation  of  these  divisions, — one  to  the  other  (fig.  357). 


Tig.  357.  Diagrammatic  view  from  befori  of  tht  parts  composing  tJu  organ  of  hearing  of  the  left 
side.  The  temporal  bone  of  the  left  side,  -with  the  accompanying  soft  parts,  has  been 
detached  from  the  head,  and  a  section  has  1  >een  carried  through  it  transversely,  so  as  to 
remove  the  front  of  the  meatus  extcmus,  half  the  tympanic  membrane,  the  upper  and 
anterior  wall  of  the  tympanum  and  Eustachian  tube.  The  meatus  internus  has  also 
been  opened,  and  the  bony  labyrinth  exposed  by  the  removal  of  the  surrounding  parts 
of  the  petrous  bone,  i,  the  pinna  and  lobe;  2,  2',  meatus  externus;  2',  membrana 
tympani ;  3,  cavity  of  the  tympanum;  3',  its  opening  backwards  into  the  mastoid 
cells ;  between  3  and  3',  the  chain  of  small  bones  ;  4,  Eustachian  tube ;  5,  meatus  in- 
ternus, containing  the  facial  (uppermost)  and  the  auditory  nerves :  6,  placed  on  the 
vestibule  of  the  labyrinth  above  the  fenestra  ovalis ;  a,  apex  of  the  petrous  bone  ; 
l>,  internal  carotid  artery ;  c,  styloid  process ;  d,  facial  nerve  issuing  from  the  stylo- 
mastoid foramen;  e,  mastoid  process  ;  /,  squamous  part  of  the  bone  covered  by  integu- 
ment, &c.     (Arnold.) 


(1.)  External  Ear. — The  external  ear  consists  of  the  pinna  or 
auricle,  and  the  external  auditory  canal  or  meatus. 

The  principal  parts  of  the  pinna  (fig.  358  a)  are  two  prominent  rims 
'enclosed  one  within  the  other  (helix  and  antihdi.r).  and  enclosing  a  central 
hollowT  named  the  conclia  ;  in  front  of  the  concha,  a  prominence  directed 
backwards,  the  tragus,  and  opposite  to  this,  one  directed  forwards,  the 
antitragus.  From  the  concha,  the  auditory  canal,  with  a  slight  arch  directed 
upwards,  passes  inwards  and  a  little  forwards  to  the  membrana  tympani,  to 
which  it  thus  serves  to  convey  the  vibrating  air.  Its  outer  part  consists  of 
fibro-cartilage  continued  from  the  concha  ;  its  inner  part  of  bone.  Both 
are  lined  by  skin  continuous  with  that  of  the  pinna,  and  extending  over  the 
outer  part  of  the  membrana  tympani. 


CHAP,  xix.] 


EXTERNAL    EAR— MIDDLE  EAR. 


$73 


Towards  the  outer  part  of  the  canal  are  fine  hairs  and  sebaceous 
glands,  while  deeper  in  the  canal  are  small  glands,  resembling  the 
Bweat-glandfl  in  structure  which  secrete  a  peculiar  yellow  substance 
called  cerunu  a,  or  car-wax. 

(2.)  Middle  Far  or  Tympanum. — The  middle  ear,  or  tympanum 
{3,  fig.  357),  is  separated  by  the  membrana  tympani  from  the 
external  auditory  canal.  It  is  a  cavity 
in  the  temporal  bone,  opening  through  its 
anterior  and  inner  wall  into  the  Eustachian 
tube,  a  cylindriform  flattened  canal,  dilated 
at  both  ends,  composed  partly  of  bone  and 
partly  of  cartilage,  and  lined  with  mucous 
membrane,  which  forms  a  communication 
between  the  tympanum  and  the  pharynx. 
It  opens  into  the  cavity  of  the  pharynx 
just  behind  the  posterior  aperture  of  the 
nostrils.  The  cavity  of  the  tympanum 
communicates  posteriorly  with  air-cavities, 
the  mastoid  cells  in  the  mastoid  process  of 
the  temporal  bone ;  but  its  only  opening 
to  the  external  air  is  through  the  Eusta- 
chian tube  (4,  fig.  357).  The  walls  of 
the  tympanum  are  osseous,  except  where 
apertures  in  them  are  closed  with  membrane,  as  at  the  fenestra 
rotunda,  and  fenestra  ovalis,  and  at  the  outer  part  where  the 
bone  is  replaced  by  the  membrana  tympani.  The  cavity  of  the 
tympanum  is  lined  with  mucous  membrane,  the  epithelium  of 
which  is  ciliated  and  continuous  with  that  of  the  pharynx.  It 
contains  a  chain  of  small  bones  (ossictda  auditus)  which  extends 
from  the  membrana  tympani  to  the  fenestra  ovalis. 


Fig.  358. —  Outer  surface  of 
the  pinna  of  the  right  auri- 
cle. 1,  helix;  2,  fossa  of 
the  helix ;    3,    antihelix ; 

4,  fossa  of  the  antihelix ; 

5,  antitragus  ;    6,  tragus  ; 
7,  concha  ;  8,  lobule.    §. 


The  membrana  tympani  is  placed  in  a  slanting  direction  at  the  bottom  of 
the  external  auditory  canal,  its  plane  being  at  an  angle  of  about  45°  with 
the  lower  wall  of  the  canal.  It  is  formed  chiefly  of  a  tough  and  tense 
fibrous  membrane,  the  edges  of  which  are  set  in  a  bony  groove  ;  its  outer  surface 
is  covered  with  a  continuation  of  the  cutaneous  lining  of  the  auditory  canal,  its 
inner  surface  with  part  of  the  ciliated  mucous  membrane  of  the  tympanum. 

The   small  bones   or    omelet    of    the    ear    are    three  ;  named    malleus, 

■'incus,  and  stapes.      The   malleus,  or  hammer-bone,  is  attached  by  a  long 

slightly-curved  process,  called  its  handle,  to  the  membrana  tympani  ;  the 

ft  attachment  being  vertical,  including  the  whole  length  of  the  handle, 

and  extending  from  the  upper  border  to  the  centre  of  the  membrane.     The 

X  X 


674  THE    SENSES.  [chap.  xix. 

head  of  the  malleus  is  irregularly  rounded  ;  its  neck,  or  the  line  of  boundary 
between  it  and  the  handle,  supports  two  processes  ;  a  short  conical  one, 
which  receives  the  insertion  of  the  tensor  tympani,  and  a  slender  one, 
jjroeessu.s  gracilis,  which  extends  forwards,  and  to  which  the  laxator  tym- 
jjani  muscle  is  attached.  The  incus,  or  anvil-bone,  shaped  like  a  bicuspid 
molar  tooth,  is  articulated  by  its  broader  part,  corresponding  with  the  sur- 
face of  the  crown  of  a  tooth,  to  the  malleus.  Of  its  two  fang-like  proces- 
one,  directed  backwards,  has  a  free  end  lodged  in  a  depression  in  the  mastoid 
bone  ;  the  other,  curved  downwards  and  more  pointed,  articulates  by  means 
of  a  roundish  tubercle,  formerly  called  os  orbiculare,  with  the  stapes,  a  little 
bone  shaped  exactly  like  a  stirrup,  of  which  the  base  or  bar  fits  into  the 
fenestra  ovalis.  To  the  neck  of  the  stapes,  a  short  process,  corresponding; 
with  the  loop  of  the  stirrup,  is  attached  the  stapedius  muscle. 

The  Ossicula. — The  bones  of  the  ear  are  covered  with  mucous 
membrane  reflected  over  them  from  the  wall  of  the  tympanum  • 
and  are  movable  both  altogether  and  one  upon  the  other.  The 
malleus  moves  and  vibrates  with  every  movement  and  vibration 
of  the  membrona  tympani,  and  its  movements  are  communicated 
through  the  incus  to  the  stapes,  and  through  it  to  the  membrane 
closing  the  fenestra  ovalis.  The  malleus,  also,  is  movable  in  its 
articulation  with  the  incus  ;  and  the  membrana  tympani  nioving 
with  it  is  altered  in  its  degree  of  tension  by  the  laxator  and  tens 
tympani  muscles.  The  stapes  is  movable  on  the  process  of  the 
incus,  when  the  stapedius  muscle  acting,  draws  it  backwards. 
The  axis  round  which  the  malleus  and  incus  rotate  is  the  line 
joining  the  processus  gracilis  of  the  malleus  and  the  posterior 
(short)  process  of  the  incus. 

(3.)  Interna.!  Ear. — The  proper  organ  of  hearing  is  formed  by 
the  distribution  of  the  auditory  nerve  within  the  internal  ear,  or 
labyrinth  of  the  ear,  a  set  of  cavities  within  the  petrous  portion 
of  the  temporal  bone.  The  bone  which  forms  the  walls  of  these 
cavities  is  denser  than  that  around  it,  and  forms  the  osseous 
labyrinth;  the  membrane  within  the  cavities  forms  the  membranous 
labyrinth.  The  membranous  labyrinth  contains  a  fluid  called 
endoh/mph  :  while  outside  it,  between  it  and  the  osseous  labyrinth, 
is  a  fluid  called  perilymph. 

The  osseous  labyrinth  consists  of  three  principal  parts,  namely, 
the  vestibide,  the  cochlea,  and  the  semicircvdar  canals. 

The  vestibule  is  the  middle  cavity  of  the  labyrinth,  and  the  central  organ 
of  the  whole  auditory  apparatus.  It  presents,  in  its  inner  wall,  several 
openings  for  the  entrance  of  the  divisions  of  the  auditory  nerve  ;  in  its  outer 
wall,  the  fenestra  ovalis  (2,  fig.  359),  an  opening  filled  by  the  base  of  the 


CIIAI".   XIX.  ] 


INTERNAL  EAR. 


675 


ttdp6s,one  at  the  Bmall  bones  of  the  ear;  in  its  posterior  and  Buperibr  walls, 
five  openings  by  which  the  semicircular  canals  communicate  with  it  :  in  its 
anterior  wall,  an  opening  Leading  into  the  cochlea.  The  binder  pari  <>f  the 
inner  wall, of  the  vestibule  also  presents  an  opening,  the  orifice  of  the  aqua- 
ductus  vestibuli,  a  canal  leading  to  the  posterior  margin  of  the  petrous  bone, 
with  uncertain  contents  and  unknown  purpose. 

The  semicircular  canals  (hgs.  359,  360),  are   three  arched  cylindriform 
bony  canals,  set  in  the  substance  of  the  petrous  bone.   They  all  open  at  both 


Fig.  359. — Rightiony  htbyrinth,xiev>edi  from 
the  outer  side.  The  specimen  here  re- 
presented is  prepared  by  separating" 
piecemeal  the  looser  substance  of  the 
petrous  bone  from  the  dense  walls  which 
immediately  enclose  the  labyrinth,  i, 
the  vestibule  ;  2,  fenestra  ovalis  ;  3,  su- 
perior semicircular  canal ;  4,  horizontal 
or  external  canal ;  5,  posterior  canal ; 
•,  ampulla?  of  the  semicircular  canals  ; 
6,  first  turn  of  the  cochlea;  7,  second 
turn;  8,  apex;  9,  fenestra  rotunda.  The 
smaller  figure  in  outline  below  shows 
the  natural  size.    ?J#     (Summering.) 


Fig.  360. —  View  of  the  interior  of  the  left 
labyrinth.  The  bony  wall  of  the  laby- 
rinth is  removed  superiorly  and  exter- 
nally. 1,  fovea  hemielliptica  ;  2,  fovea 
hemispherica ;  3,  common  opening  of 
the  superior  and  posterior  semicircular 
canals  ;  4,  opening  of  the  aqueduct  of 
the  vestibule  ;  5,  the  superior,  6,  the 
posterior,  and  7,  the  external  semicir- 
cular canals ;  8,  spiral  tube  of  the 
cochlea  (scala  tympani)  ;  9,  opening  of 
the  aqueduct  of  the  cochlea  ;  10,  placed 
on  the  lamina  spiralis  in  the  scala  vesti- 
buli.      ij     (Summering.) 


ends  into  the  vestibule  (two  of  them  first  coalescing).  The  ends  of  each  are 
dilated  just  before  opening  into  the  vestibule  ;  and  one  end  of  each  being 
more  dilated  than  the  other  is  called  an  ampulla.  Two  of  the  canals  form 
nearly  vertical  arches;  of  these  the  superior  is  also  anterior ;  the  posterior 
is  inferior  ;  the  third  canal  is  horizontal,  and  lower  and  shorter  than  the 
others. 

The  coclrf en  (6,  7,  8,  figs.  359  and  360),  a  small  organ,  shaped  like  a  com- 
mon snail-shell,  is  seated  in  front  of  the  vestibule,  its  base  resting  on  the 
bottom  of  the  internal  meatus,  where  some  apertures  transmit  to  it  the 
cochlear  filaments  of  the  auditory  nerve.  In  its  axis,  the  cochlea  is  traversed 
by  a  conical  column,  the  modiolus,  around  which  a  spiral  canal  winds  with 
about  two  turns  and  a  half  from  the  base  to  the  apex.  At  the  apex  of  the 
cochlea  the  canal  is  closed  ;  at  the  base  it  presents  three  openings,  of  which 
one,  already  mentioned,  communicates  with  the  vestibule  ;  another  called 
fenestra  rotunda,  is  separated  by  a  membrane  from  the  cavity  of  the  tym- 

x  x  2 


6y6 


THE    SENSES. 


[CHAP.  XIX. 


cochlea 

central 


*^ssa2e^£§z5  ^55^=--^ 


Fig.  361.  —  View  of  the  osseous 
divided  through  the  middle. 
canal  of  the  modiolus  :  2,  lamina  spi- 
ralis ossea  :  3,  scala  tympani ;  4.  scala 
vestibuli;  5,  porous  substance  of  the 
modiolus  near  one  of  the  sections  of 
the  canalis  spiralis  modioli,  f.  ^Arnold.) 


panum  ;  the  third  is  the  orifice  of  the  aqiueduetus  cochlea*,  a  canal  leading 
to  the  jugular  fossa  of  the  petrous  bone,  and  corresponding,  at  least  iu 
obscurity  of  purpose  and  origin,  to  the  aquaeductus  vestibuli.     The  spiral 

canal  is  divided  into  two  passages,  or 
scahe,  by  a  partition  of  bone  and 
membrane,  the  lamina  spiralis.  The 
osseous  part  or  zone  of  this  lamina  is 
connected  with  the  modiolus  ;  the 
membranous  part,  with  a  muscular 
zone,  according  to  Todd  and  Bowman, 
forming  its  outer  margin,  is  attached 
to  the  outer  wall  of  the  canal.  Com- 
mencing at  the  base  of  the  cochlea, 
between  its  vestibular  and  tympanic 
openings,  they  form  a  partition  be- 
tween these  apertures  ;  the  two  scalse 
are.  therefore,  in  correspondence  with 
this  arrangement,  named  scala  vesti- 
buli and  scala  tympani  (fig. 361).  At 
the  apex  of  the  cochlea,  the  lamina 
spiralis  ends  in  a  small  hamulus,  the  inner  and  concave  part  of  which,  being 
detached  from  the  summit  of  the  modiolus,  leaves  a  small  aperture  named 

helicotrema,  by  which  the 
two  scalge,  separated  in  all 
the  rest  of  their  length, 
communicate. 

Besides  the  "  scala  vesti- 
buli "  and  "'scala  tympani," 
there  is  a  third  space  be- 
tween them,  called  scala 
media  ©r  canalis  membra- 
naceus  (CC.  fig.  362).  In 
section  it  is  triangular,  its 
external  wall  being  formed 
by  the  wall  of  the  cochlea, 
its  upper  wall  (separating 
it  from  the  scala  vestibuli) 
by  the  membrane  of  Beiss- 
ner,  and  its  lower  wall 
(separating  it  from  the 
scala  tympani)  by  the 
basilar  membrane,  these 
two  meeting  at  the  outer 
edge  of  the  bony  lamina 
spiralis.  Following  the 
turns  of  the  cochlea  to  its 
apex,  the  scala  media  there  terminates  blindly  ;  while  towards  the  base  of 
the  cochlea  it  is  also  closed  with  the  exception  of  a  very  narrow  pa  - 
(canalis  reuniens)  uniting  it  with  the  sacculus.  The  scala  media  (like  the 
rest  of  the  membranous  labyrinth)  contains  "endolymph.'' 

Org-an  of  Corti. — Upon  the  basilar  membrane  are  arranged    cells  of 
various  shapes. 


Fig.  362. — .Section  through  one  of  the  coils  of  the  cochlea 
(diagrammatic).  8  T,  scala  tympani;  8  V,  scala 
[ball ;  C  C\  canalis  cochlefe  or  canalis  membra- 
naceus  ;  JR,  membrane  of  Fieissner  ;  I  s  o%  lamina 
spiralis  ossea  ;  lis.  limbus  laminte  spiralis ;  s  s, 
sulcus  spiralis  ;  n  c,  cochlear  nerve  ;  g  s.  ganglion  spi- 
rale ;  t,  membrana  tectoria  ;  'below  the  membrana 
tectoria  is  the  lamina  reticularis ; )  b,  membrana 
baaflaris  :  Co,  rods  of  Corti  ;  I  sp,  ligamentum  spirale. 
From  Quoin' 8  Anatomy.) 


CHAP.  XIX.] 


[NTEKNAL   EAR. 


$77 


About  midway  between  the  outer  edge  of  the   hmina   spiralis  and  the 
outer  wall  of  the  cochl  tnated  the  ra 

the  r  n  to  con-i-t  <>f  an  external  and  internal  pilla:. 

fn>m  an  expanded  foot  or  bate  on  the  basilar  mem  bran-  .  j  slant 


" 


Fig.  363.—  P  "  the  organ  of  Corti  from  the  dog.    1  to  2,  homogeneous  layer  of 

the  so-called  membrana  basi.  stfbular  1 .  rnpanal  layer,  •with  nuclei 

and  protoplasm ;  a,  prolongation  of  tympanal  periosteum  of  lamina  spiralis  1  - 
c.  thickened  commencement  of  the  membrana  basilaris  near  the  point  of  perforation  of 
the  nerves  1  ;  d,  blood-vessel   vas  spirale}  ;  e,  blood-vessel :  /.  £•  the  epithe- 

lium of  the  sulcus  spiralis  internus  :  1",  internal  or  tufted  cell,  with  basil  proce>?  fc,  sur- 
rounded with  nuclei  and  protoplasm  (of  the  granular  layer  ,  into  which  thei 
fibres  radiate :  J,  hairs  of  the  internal  hair-cell ;  n,  base  or  foot  of  inner  pillar  of  organ 
of  Corti :  m,  head  of  the  same  uniting  with  the  corresponding  part  of  an  external 
pillar,  whose  under  half  is  missing,  while  the  next  pillar  beyond,  o.  presents  both 
middle  portion  and  base ;  r,  s,  d,  three  external  hair  cells  ;  /,  bases  of  two  nei?hbour- 
ing  hair  or  tufted  cells;  x,  so-called  supporting  cell  of  Hensen:  m,  nerve-fibre 
terminating  in  the  first  of  the  external  hair-cells ;  I  I  to  I,  lamina  reticularis,  x  800. 
Waldej 


inwards  towards  each  other,  and  each  ends  in  a  swelling  termed  the  head  ; 
the  head  of  the  inner  pillar  overlying  that  of  the  outer  (fig.  363).  Each 
pair  of  pillars  forms,  as  it  were,  a  pointed  roof  arching  over  a  space,  and  by 
a  succession  of  them,  a  little  tunnel  is  formed. 

It  has  been  estimated  that  there  are  about  3000  of  these  pairs  of  pillars, 
in  proceeding  from  the  base  of  the  cochlea  towards  its  apex.  They  are 
found  -  ssively  to  increase  in  length,  and  become  more  obliqi; 
other  words,  the  tunnel  becomes  wider,  but  diminishes  in  height  as  we 
approach  the  apex  of  the  cochlea.  Leaning,  as  it  were,  against  these  ex- 
ternal and  internal  pillars  are  certain  other  cells,  of  which  the  external  ones 
terminate  in  small  hair-like  pro  asea,  If  -:  of  the  above  details  are  shown 
in  the  accompanying  figure  (fig.  363).  This  complicated  structur 
we  have  seen,  upon  the  basilar  membrane  :  it  is  roofed  in  by  a  remarkable 
rated  membrane  (lamina  reticularis  of  Kolliker)  into  the  fenestrae  of 
which  the  t<  ,ps  of  the  various  rods  and  cells  are  received.  When  viewed 
from  above,  the  organ  of  Corti  a    remarkable  resemblance  to  the 

key -board  of  a  piano.  In  close  relation  with  the  rods  of  Corti  and  the  cells 
inside  and  outside  them,  and  probably  projecting  by  free  ends  into  the 


678  THE    SENSES,  [chap.  xix. 

little  "  tunnel "  containing  fluid  (roofed  in  by  them),  are  filaments  of  the 
auditory  nerve. 

Membranous  Labyrinth. — This  corresponds  generally  with 
the  form  of  the  osseous  labyrinth,  so  far  as  regards  the  vestibule 
and  semicircular  canals,  but  is  separated  from  the  walls  of  these 
parts  by  fluid,  except  where  the  nerves  enter  into  connection 
within  it.  As  already  mentioned,  the  membranous  labyrinth 
contains  a  fluid  called  endolyph ;  and  between  its  outer  surface 
and  the  inner  surface  of  the  walls  of  the  vestibule  and  semi- 
circular canals  is  another  collection  of  similar  fluid,  called  peri- 
lymph ;  so  that  all  the  sonorous  vibrations  impressing  the  auditory 
nerves  on  these  parts  of  the  internal  ear,  are  conducted  through 
fluid  to  a  membrane  suspended  in  and  containing  fluid.  In  the 
cochlea,  the  membranous  labyrinth  completes  the  septum  between 
the  two  scalce  and  encloses  a  spiral  canal,  previously  mentioned, 
called  canalis  membranaceus  or  canal  is  cochlece  (fig.  362).  The  fluid 
in  the  scalar  of  the  cochlea  is  continuous  with  the  perilymph  in  the 
vestibule  and  semicircular  canals,  and  there  is  no  fluid  external  to 
its  lining  niembrane.  The  vestibular  portion  of  the  membranous 
labyrinth  comprises  two,  probably  communicating  cavities,  of 
which  the  larger  and  upper  is  named  the  utriculus ;  the  lower, 
the  sacculus.  They  are  lodged  in  depressions  in  the  bony  laby- 
rinth termed  respectively  "fovea  hemielliptica"  and  "fovea 
hemispherica."  Into  the  former  open  the  orifices  of  the  mem- 
branous semcircular  canals  ;  into  the  latter  the  canalis  cochlece. 
The  membranous  labyrinth  of  all  these  parts  is  laminated,  trans- 
parent, very  vascular,  and  covered  on  the  inner  surface  with 
nucleated  cells,  of  which  those  that  line  the  ampulla;  are  pro- 
longed into  stiff  hair-like  processes ;  the  same  appearance,  but  to 
a  much  less  degree,  being  visible  in  the  utricule  and  saccule.  In 
the  cavities  of  the  utriculus  and  sacculus  are  small  masses  of 
calcareous  particles,  otoconia  or  otoliths;  and  the  same,  although 
in  more  minute  quantities,  are  to  be  found  in  the  interior  of  some 
other  parts  of  the  membranous  labyrinth. 

Auditory  Nerve. — For  the  appropriate  exposure  of  the  fila- 
ments of  the  auditory  nerve  to  sonorous  vibrations  all  the  organs 
now  described  are  provided.  It  is  characterised  as  a  nerve  of 
special  sense  by  its  softness  (whence  it  derived  its  name  of  portio 
mollis  of  the  seventh  pair),  and  by  the  fineness  of  its  component 


OHAP,  xix.]  FUNCTIONS   OF    EXTERNAL  EAl;.  (yjg 

fibres.  It  enters  the  labyrinth  of  the  ear  in  two  divisions;  one 
for  the  vestibule  and  semicircular  canals,  and  the  other  for  the 
cochlea. 

The  branches  for  the  vestibule  spread  out  and  radiate  od  the 
inner  surface  of  the  membranous  labyrinth  :  their  exact  termina- 
tion is  unknown.  Those  for  the  semicircular  canals  pass  into  the 
ampullae,  and  form,  within  each  of  them,  a  forked  projection  which 
corresponds  with  a  septum  in  the  interior  of  the  ampulla.  The 
branches  for  the  cochlea  enter  it  through  orifices  at  the  base  of  the 
modiolus,  which  they  ascend,  and  thence  successively  pass  into 
canals  in  the  osseous  part  of  the  lamina  spiralis.  In  the  canals  of 
this  osseous  part  or  zone,  the  nerves  are  arranged  in  a  plexus, 
containing  ganglion  cells.  Their  ultimate  termination  is  not 
known  with  certainty  ;  but  some  of  them,  without  doubt,  end  in 
the  organ  of  Corti,  probably  in  cells. 


Physiology  of  Hearing. 

All  the  acoustic  contrivances  of  the  organ  of  hearing  are  means 
for  conducting  the  sound,  just  as  the  optical  apparatus  of  the  eye 
lire  media  for  conducting  the  light.  Since  all  matter  is  capable  of 
propagating  sonorous  vibrations,  the  simplest  conditions  must  be 
sufficient  for  mere  hearing ;  for  all  substances  surrounding  the 
auditory  nerve  would  communicate  sound  to  it.  The  whole  de- 
velopment of  the  organ  of  hearing,  therefore,  can  have  for  its 
object  merely  the  rendering  more  perfect  the  propagation  of  the 
sonorous  vibrations,  and  their  multiplication  by  resonance  \  and, 
in  fact,  all  the  acoustic  apparatus  of  the  organ  may  be  shown  to 
have  reference  to  these  two  principles. 

Functions  of  the  External  Ear. — The  external  auditory 
passage  influences  the  propagation  of  sound  to  the  tympanum  in 
three  ways  : — i,  by  causing  the  sonorous  undulations,  entering 
directly  from  the  atmosphere,  to  be  transmitted  by  the  air  in  the 
passage  immediately  to  the  membrana  tympani,  and  thus  prevent- 
ing them  from  being  dispersed;  2,  by  the  walls  of  the  passage 
conducting  the  sonorous  undulations  imparted  to  the  external  ear 
itself,  by  the  shortest  path  to  the  attachment  of  the  membrana 
tympani,  and  so  to  this  membrane  ;  3,  by  the  resonance  of  the 
column  of  air  contained  within  the  passage  ;    4,  the  external  ear, 


680  THE    SENSES.  [chap.  xix. 

especially  when  the  tragus  is  provided  with  hairs,  is  also,  doubtless, 
of  service  in  protecting  the  meatus  and  membrana  tympani  against 
dust,  insects,  and  the  like. 

i.  As  a  conductor  of  undulations  of  air,  the  external  auditory  passage 
receives  the  direct  undulations  of  the  atmosphere,  of  which  those  that  enter 
in  the  direction  of  its  axis  produce  the  strongest  impressions.  The  undula- 
tions which  enter  the  passage  obliquely  are  reflected  by  its  parietes,  and  thus 
by  reflexion  reach  the  membrana  tympani. 

2.  The  walls  of  the  meatus  are  also  solid  conductors  of  sound  ;  for  those 
vibrations  which  are  communicated  to  the  cartilage  of  the  external  ear,  and 
not  reflected  from  it,  are  propagated  by  the  shortest  path  through  the 
parietes  of  the  passage  to  the  membrana  tympani.  Hence,  both  ears  being 
close  stopped,  the  sound  of  a  pipe  is  heard  more  distinctly  when  its  lower 
extremity,  covered  with  a  membrane,  is  applied  to  the  cartilage  of  the 
external  ear  itself,  than  when  it  is  placed  in  contact  with  the  surface  of 
the  head. 

3.  The  external  auditory  passage  is  important,  inasmuch  as  the  air  which 
it  contains,  like  all  insulated  masses  of  air,  increases  the  intensity  of  sounds 
by  resonance. 

Regarding  the  cartilage  of  the  external  ear,  therefore,  as  a  con- 
ductor of  sonorous  vibrations,  all  its  inequalities,  elevations,  and 
depressions,  which  are  useless  with  regard  to  reflexion,  become  of 
evident  importance ;  for  those  elevations  and  depressions  upon 
which  the  undulations  fall  perpendicularly,  will  be  affected  by 
them  in  the  most  intense  degree  ;  and,  in  consequence  of  the 
various  forms  and  positions  of  these  inequalities,  sonorous  undula- 
tions, in  whatever  direction  they  may  come,  must  fall  perpendicu- 
larly upon  the  tangent  of  some  one  of  them.  This  affords  an 
explanation  of  the  extraordinary  form  given  to  this  part. 

Functions  of  the  Middle  Ear. — In  animals  living  in  the 
atmosphere,  the  sonorous  vibrations  are  conveyed  to  the  auditory 
nerve  by  three  different  media  in  succession  ;  namely,  the  air,  the 
solid  parts  of  the  body  of  the  animal  and  of  the  auditory  apparatus, 
and  the  fluid  of  the  labyrinth.  Sonorous  vibrations  are  imparted 
too  imperfectly  from  air  to  solid  bodies,  for  the  propagation  of 
sound  to  the  internal  ear  to  be  adequately  effected  by  that  means 
alone  ;  yet  already  an  instance  of  its  being  thus  propagated  has 
been  mentioned.  In  passing  from  air  directly  into  water,  sonorous 
vibrations  suffer  also  a  considerable  diminution  of  their  strength  ; 
but  if  a  tense  membrane  exists  between  the  air  and  the  water,  the 
sonorous  vibrations  are  communicated  from  the  former  to  the  latter 
medium  with  very  great  intensity.     This  fact,  of  which  Miiller 


.hyp.  xix.]  FUNCTIONS  0*  MIDDLE   BAB.  68l 

gives  experimental  proofj  furnish  an  explanation  of  the 

use  of  th  •  ra   rotunda,   and  of  the  membrane  closing  it. 

They  are  the  means  of  commnnicating,  in  full  intensity,  the 
vibrations  of  the  air  in  the  tympanum  to  the  fluid  of  the  labyrinth* 
This  peculiar  property  of  membranes  is  the  result,  not  of  their 
tenuity  al«»ue,  but  of  the  elasticity  and  capability  of  displacement 
of  their  particles  ;  and  it  is  not  impaired  when,  like  the  membrane 
of  the  fenestra  rotunda,  they  are  not  impregnated  with  moistui 

S  Lorous  vibrations  are  also  communicated  without  any  per- 
ceptible loss  of  intensity  from  the  air  to  the  water,  when  to  the 
membrane  forming  the  medium  of  communication,  there  is  at- 
tached a  short,  solid  body,  which  occupies  the  greater  part  of  its 
-  face,  and  is  alone  in  contact  with  the  water.  This  fact  eluci- 
dates the  action  of  the  fenestra  oralis,  and  of  the  plate  of  the 
si  ipes  which  occupies  it,  and,  with  the  preceding  fact,  shows  that 
both  fenestra? — that  closed  by  membrane  only,  and  that  with  which 
the  movable  stapes  is  connected — transmit  very  freely  the 
sonorous  vibrations  from  the  air  to  the  fluid  of  the  labyrinth. 

A  -mall,  solid  body,  fixed  in  an  opening  by  means  of  a  border 
of  membrane,  bo  as  to  be  movable,  communicates  sonorous  vibra- 
tions from  air  on  the  one  side,  to  water,  or  the  fluid  of  the 
lal  tyrinth,  on  the  other  side,  much  better  than  solid  media  not  s 
constructed.  But  the  propagation  of  sound  to  the  fluid  is  ren- 
dered much  more  perfect  if  the  solid  conductor  thus  occupying 
the  opening,  or  fenestra  ovalis,  is  by  its  other  end  fixed  to  the 
middle  of  a  tense  membrane,  which  has  atmospheric  air  on  both 
sides.  A  tense  membrane  is  a  much  better  conductor  of  the 
vibrations  of  air  than  any  other  solid  body  bounded  by  definite 
surfaces  :  and  the  vibrations  are  also  communicated  very  readily 
1  >y  tense  meml  iranes  to  solid  bodies  in  contact  with  them.  Thusr 
then,  the  ma&brana  tympani  serves  for  the  transmission  of  sound 
from  the  air  to  the  chain  of  auditory  bones.  Stretched  tightly  in 
its  osseous  ring,  it  vibrates  with  the  air  in  the  auditory  passage, 
-  any  thin  tense  membrane  will,  when  the  air  near  it  is  thrown 
into   vibrations  by   the  sounding  of  a    tuning-fork   or  a   musical 

ing.  And,  from  such  a  tense  vibrating  membrane,  the  vibra- 
tions are  communicated  with  great  intensity  to  solid  bodies  which 
touch  it  at  any  point.  If,  for  example,  one  end  of  a  flat  piece  of 
wood  be  applied  to  the  membrane  of  a  drum,  while  the  other  end 


682  THE    SENSES.  [chai\  xix. 

is  held  in  the  hand,  vibrations  are  felt  distinctly  when  the 
vibrating  tuning-fork  is  held  over  the  membrane  without  touching 
it  ;  but  the  wood  alone,  isolated  from  the  membrane,  will  only 
very  feebly  propagate  the  vibrations  of  the  air  to  the  hand. 

In  comparing  the  membrana  tympani  to  the  membrane  of  a  drum,  it  is 
necessary  to  point  out  certain  important  differences. 

"When  a  drum  is  struck,  a  certain  definite  Tone  is  elicited  (fundamental 
tone)  ;  similarly  a  drum  is  thrown  into  vibration  when  certain  tones  are 
sounded  in  its  neighbourhood,  while  it  is  quite  unaffected  by  others.  In 
other  words,  it  can  only  take  up  and  vibrate  in  response  to  those  tones  whose 
vibrations  nearly  correspond  in  number  with  those  of  its  own  fundamental 
tone.  The  tympanic  membrane  can  take  up  an  immense  range  of  tones  pro- 
duced by  vibrations  ranging  from  30  to  4000  or  5000  per  second.  This 
would  be  clearly  impossible  if  it  were  an  evenly  stretched  membrane. 

The  fact  is.  that  the  tympanic  membrane  is  by  no  means  evenly  stretched, 
and  this  is  due  partly  to  its  slightly  funnel-like  form,  and  partly  to  its  being 
•connected  with  the  chain  of  auditory  ossicles.  Further,  if  the  membrane 
were  quite  free  in  its  centre,  it  would  go  on  vibrating  as  a  drum  does  some 
time  after  it  is  struck,  and  each  sound  would  be  prolonged,  leading  to  con- 
siderable confusion.  This  evil  is  obviated  by  the  ear-bones,  which  check  the 
•continuance  of  the  vibrations  like  the  ';  dampers  "  in  a  pianoforte. 

The  ossicula  of  the  ear  are  the  better  Conductors  of  the  sonorous 
vibrations  communicated  to  them,  on  account  of  being  isolated  by 
an  atmosphere  of  air,  and  not  continuous  with  the  bones  of  the 
cranium  ;  for  every  solid  body  thus  isolated  by  a  different  medium, 
propagates  vibrations  with  more  intensity  through  its  own  sub- 
stance than  it  communicates  them  to  the  surrounding  medium, 
which  thus  prevents  a  dispersion  of  the  sound ;  just  as  the  vibra- 
tions of  the  air  in  the  tubes  used  for  conducting  the  voice  from  one 
apartment  to  another  are  prevented  from  being  dispersed  by  the 
solid  walls  of  the  tube.  The  vibrations  of  the  membrana  tympani 
are  transmitted,  therefore,  by  the  chain  of  ossicula  to  the  fenestra 
ovalis  and  fluid  of  the  labyrinth,  their  dispersion  in  the  tympanum 
being  prevented  by  the  difficulty  of  the  transition  of  vibrations 
from  solid  to  gaseous  bodies. 

The  necessity  of  the  presence  of  air  on  the  inner  side  of  the 
membrana  tympani,  in  order  to  enable  it  and  the  ossicula  auditus 
to  fulfil  the  objects  just  described,  is  obvious.  Without  this 
provision,  neither  would  the  vibrations  of  the  membrane  be  free, 
nor  the  chain  of  bones  isolated,  so  as  to  propagate  the  sonorous 
undulations  with  concentration  of  their  intensity.  But  while  the 
'  oscillations  of  the  membrana  tympani  are  readily  communicated 


<  hap.  xix. J  PUNCTIOlfS  OF  088ICULA.  683 

t«»  the  ear  in  the  cavity  of  the  tympanum,  those  of  the   - 
ula  will  not  be  conducted  away  by  the  air,  but  will  be  propa- 

•    1  to  the  labyrinth  without  being  di  in  the  tympanum. 

The  propagation  of  sound  through  the  ossicula  of  the  tympanum 
to  the  labyrinth,  must  be  effected  either  by  oscillations  of  the  1 
or  by  a  kind  of  molecular  vibration  <'f  their  particles,  or,  most 
probably,  by  both  these  kinds  of  motion, 

M  -      ••  'i-uJa. — E.  Weber  has  shown  that  the  existence  of  the 

membrane  over  the  fen  mda  will  permit  approximation  and  removal 

<>f  ti  to  and  from  the  labyrinth.     When  by 

■  membrane  of  the  fenestra  ova', 
the  labyrinth,  the  membrane  of 
the  fenestra  rotunda  may,  by  the  |  commu- 

nicated  through   the    fluid    of    the   labyrinth,  be 
-  -lie  cavity  of  the  tympanum. 
The   lone   process   of    the   malleus   receives   the 
undulations  of  the  membra na  tympani  (fig.  364.  a.  a) 
and  of  the  air  in  a  direction  indicated  by  the  an 
nearly  perpendicular  to  itself.     From  the  lone  pro- 
of   the  malleus  they  are   propagated   b 
head  (Z>)  :  thence  into  the  incus  (e)t  the  lone  pro- 

-  of  which  is  parallel  with  the  long  pi 
the  malleus.  From  the  lone  process  of  the  incus 
the  undulations  are  communicated  to  the  stapes  (d) 
which  is  united  to  the  incus  at  right  angles.  The 
al  changes  in  the  direction  of  the  chain  of 
bones  have,  however,  no  influence  on  that  of   the  j.^     , 

undulations,  which  remain  the  same  as  it  was  in  the 

meatus  externus  and  lone  process  of  the  malleus,  so  that  the  undulations  are 
communicated  by  the  stapes  to  the  fenestra  oralis  in  a  perpendicular  direction. 

Increasing  tension  of  the  membrana  tympani  diminishes  the 
facility  of  transmissi<  »n  of  »  morons  undulations  from  the  air  to  it. 

Savart  observed  that  the  dry  membrana  tympani.  on  the  approach  of  a 
body  emitting  a  loud  sound,  rejected  particles  of  sand  strewn  upon  it  more 
strongly  when  lax  than  when  very  tense  ;  and  inferred,  therefore,  that  hear- 
ing is  rendered  less  acute  by  increasing  the  tension  of  the  membrana  tym- 
pani. Muller  has  confirmed  this  by  experiments  with  small  membranes 
arranged  so  as  to  imitate  the  membrana  tympani ;  and  it  may  be  confirmed 
also  by  observations  on  on  '- 

The  pharyngeal  orifice  of   the  Eustachian  tube  is   usually  shut ;  during 

allowing,  however,  it   is   opened:  this   may  be   sh  -  wb: — If 

the  nose  and  mouth  be  closed  and  the  cheeks  blown  out.  a  sense  of  pressure 
-  produced  in  both  ears  the  moment  we  swallow  ;  this  is  due.  dou 
the  bulging  out  of  the  tympanic  membrane  by  the  compressed  air  which,  at 
that  moment,  enters  the  Eustachian  tube. 

Similarly  the  tympanic  membrane  may  be  in  by  rarefying  the  air 

in  the  tympanum.     This  can  be  readily  accomplished  by  closing  the  mouth 


684  THE  SEXSES«  [°HAP- XIX- 

and  nose,  and  making  an  inspiratory  effort  and  at  the  same  time  swallowing 
(Valsalva).  In  both  cases  the  sense  of  hearing  is  temporarily  dulled  ; 
proving  that  equality  of  pressure  on  both  sides  of  the  tympanic  membrane 
is  necessary  for  its  full  efficiency. 

Functions  of  Eustachian  Tube. — The  principal  office  of  the 
Eustachian  tube,  in  Muller's  opinion,  has  relation  to  the  prevention 
of  these  effects  of  increased  tension  of  the  membrana  tympani. 
Its  existence  and  openness  will  provide  for  the  maintenance  of  the 
equilibrium  between  the  air  within  the  tympanum  and  the  exter- 
nal air,  so  as  to  prevent  the  inordinate  tension  of  the  membrana 
tympani  which  would  be  produced  by  too  great  or  too  little 
pressure  on  either  side.  While  discharging  this  office,  however,  it 
will  serve  to  render  sounds  clearer,  as  (Henle  suggests)  the  aper- 
tures in  violins  do ;  to  supply  the  tympanum  with  air  ;  and  to  be 
an  outlet  for  mucus.  If  the  Eustachian  tube  were  "permanently 
open,  the  sound  of  one's  own  voice  would  probably  be  greatly 
intensified,  a  condition  which  would  of  course  interfere  with  the 
perception  of  other  sounds.  At  any  rate,  it  is  certain  that  sonorous 
vibrations  can  be  propagated  up  the  Eustachian  tube  to  the  tym- 
panum by  means  of  a  tube  inserted  into  the  pharyngeal  orifice  of 
the  Eustachian  tube. 

Action  of  Tensor  Tympani. — The  influence  of  the  tensor 
tympani  muscle  in  modifying  hearing  may  also  be  probably  ex- 
plained in  connection  with  the  regulation  of  the  tension  of  the 
membrana  tympani.  If,  through  reflex  nervous  action,  it  can  be 
excited  to  contraction  by  a  very  loud  sound,  just  as  the  iris  and 
orbicularis  palpebrarum  muscle  are  by  a  very  intense  light,  then  it 
is  manifest  that  a  very  intense  sound  would,  through  the  action  of 
this  muscle,  induce  a  deafening  or  muffling  of  the  ears.  In  favour 
of  this  supposition  we  have  the  fact  that  a  loud  sound  excites, 
by  reflection,  nervous  action,  winking  of  the  eyelids,  and,  in  per- 
sons of  irritable  nervous  system,  a  sudden  contraction  of  many 
muscles. 

"  The  ossicula  of  aquatic  mammalia  are  very  bulky  and  relatively  large, 
especially  in  the  true  seals  and  the  sirenia  (Manatee  and  Dugong).  In  the 
cetacea  the  stapes  is  generally  ankylosed  to  the  fenestra  ovalis,  the  malleus 
is  always  ankylosed  to  the  tympanic  bone,  yet  the  membrana  tympani  is 
■well  formed,  and  there  is  a  manubrium,  often  ill-developed,  but  always 
attached  to  the  membrane  by  a  long  process.  In  the  Otarise  or  Sea-lions,, 
where  the  ossicula  are  far  smaller  relatively,  and  less  solid  than  in  whales, 


.  HAi-.  xix.]       FUNCTIONS   OP   FLUID   OF   LAIiYRIXTII.  685 

manatees,   and    the   earless    true  •■    well-formed,   movable 

nial  ears.    The  oesicula  Beem  to  be   vestigial    relics   utilized  for  the 

auditory  function.  In  land  animals  they  vary  in  shape  according  to 
type  of  the  animal  rather  than  in  relation  to  it-  1  rofheari 

I  have  never  found  a  muscular  Laxator  tympani  in  any  animal,  hut  the 
ligament  in  whales  where  the  malleus  ia  fixed.'1  (Albau 
in.) 

Action  of  the  Stapedius. — The  influence  of  the  .stapedius 
muscle  in  hearing  is  unknown.  It  acts  upon  the  stapes  in  such  a 
manner  as  to  make  it  rest  obliquely  in  the  fenestra  oralis  depress- 
ing that  side  of  it  on  which  it  acts,  and  elevating  the  other  side  to 
the  same  extent.      It  prevents  too  great  a  movement  of  the  hone. 

Functions  of  the  Fluid  of  the  Labyrinth. — The  fluid  0/  the 
labyrinth  is  the  most  genera]  and  constant  of  the  acoustic  provisions 
of  the  labyrinth.  In  all  forms  of  organs  of  hearing,  the  sonor- 
ons  vibrations  affect  the  auditory  nerve  through  the  medium  of 
liquid — the  most  convenient  medium,  on  many  accounts,  for  such 
a  purpose. 

The  crystalline  pulverulent  masses  (otoliths)  in  the  labyrinth 
would  reinforce  the  sonorous  vibrations  by  their  resonance,  even  if 
they  did  not  actually  touch  the  membranes  upon  which  the  nerves 
are  expanded  ;  but,  inasmuch  as  these  bodies  lie  in  contact  with 
the  membranous  pails  of  the  labyrinth,  and  the  vestibular  nerve- 
til  >res  are  imbedded  in  them,  they  communicate  to  these  membranes 
and  the  nerves,  vibratory  impulses  of  greater  intensity  than  the 
fluid  of  the  labyrinth  can  impart.  This  appears  to  be  their  office. 
iorous  undulations  in  water  are  not  perceived  by  the  hand  itself 
immersed  in  the  water,  but  are  felt  distinctly  through  the  medium 
of  a  rod  held  in  the  hand.  The  fine  hair-like  prolongations  from 
the  epithelial  cells  of  the  ampulke  have,  probably,  the  same 
function. 

Functions  of  the  Semicircular  Canals.— Besides  the  function 
of  collecting  in  their  fluid  contents  sonorous  undulations  from  the 
bones  of  the  cranium,  the  semicircular  canals  appear  to  have 
another  function  less  directly  connected  with  the  sense  of  hearing. 
Experiments  show  that  when  the  horizontal  canal  is  divided  in  a 
pigeon  a  constant  movement  of  the  head  from  side  to  side  occurs, 
and  similarly,  when  one  of  the  vertical  canals  is  operated  upon,  up 
and  down  movements  of  the  head  are  observed.  These  movements 
are  associated,  also,  with  loss  of  co-ordination,  as  after  the  opera- 


6S6  THE    SEXSES.  [chap,  xix. 

tion  the  bird  is  unable  to  fly  in  an  orderly  manner,  but  flutters  and 
falls  when  thrown  into  the  air,  and,  moreover,  is  able  to  feed  with 
difficulty.  Hearing  remains  unimpaired.  It  has  been  suggested,, 
therefore,  that  as  loss  of  co-ordination  results  from  section  of  these 
canals,  and  as  co-ordinate  muscular  movements  appear  to  depend 
to  a  considerable  extent  for  their  due  performance  upon  a  correct 
notion  of  our  equilibrium,  that  the  semicircular  canals  are  con- 
nected in  some  way  with  this  sense,  possibly  by  the  constant 
alterations  of  the  pressure  of  the  fluid  within  them.  The  change 
in  the  pressure  of  the  fluid  in  each  canal  which  takes  place  on  any 
movement  of  the  head,  producing  sensations  which  aid  in  forming 
an  exact  judgment  of  the  alteration  of  position  which  has 
occurred. 

Functions  of  the  Cochlea. — The  cochlea  seems  to  be  con- 
structed for  the  spreading  out  of  the  nerve-fibres  over  a  wide  extent 
of  surface,  upon  a  solid  lamina  which  communicates  with  the  solid 
walls  of  the  labyrinth  and  cranium,  at  the  same  time  that  it  is  in 
contact  with  the  fluid  of  the  labyrinth,  and  which,  besides  exposing 
the  nerve-fibres  to  the  influence  of  sonorous  undulations,  by  two 
media,  is  itself  insulated  by  fluid  on  either  side. 

The  connection  of  the  lamina  spiralis  with  the  solid  walls  of  the 
labyrinth,  adapts  the  cochlea  for  the  perception  of  the  sonorous 
undulations  propagated  by  the  solid  parts  of  the  head  and  the 
walls  of  the  labyrinth.  The  membranous  labyrinth  of  the  vesti- 
bule and  semicircular  canals  is  suspended  free  in  the  perilymph, 
and  is  destined  more  particularly  for  the  perception  of  sounds 
through  the  medium  of  that  fluid,  whether  the  sonorous  undula- 
tions be  imparted  to  the  fluid  through  the  fenestra?,  or  by  the 
intervention  of  the  cranial  bones,  as  when  sounding  bodies  are 
brought  into  communication  with  the  head  or  teeth.  The  spiral 
lamina  on  which  the  nervous  fibres  are  expanded  in  the  cochlea, 
is,  on  the  contrary,  continuous  with  the  solid  walls  of  the  laby- 
rinth, and  receives  directly  from  them  the  impulses  which  they 
transmit.  This  is  an  important  advantage  ;  for  the  impulses  im- 
parted by  solid  bodies  have,  caeteris  paribus,  a  greater  absolute 
intensity  than  those  communicated  by  water.  And,  even  when  a 
sound  is  excited  in  the  water,  the  sonorous  undulations  are  -more 
intense  in  the  water  near  the  surface  of  the  vessel  containing  it, 
than  in  other  parts  of  the  water  equally  distant  from  the  point  of 


CHAP,  xix.]  FUNCTIONS   OF   COCHLEA.  687 

origin  <»f  the  Bound  ;  thus  we  may  conclude  that,  coetcrU  paribus, 
the  Bonoroua  undulations  of  solid  bodies  act  with  -ity 

than  those  of  water.     Bence,  we  perceive  at  once  an  important 
sochlea. 

This  is  not,  however,  the  sole  office  of  the  cochlea;  the  spiral 
lamina,  as  well  as  the  membranous  labyrinth,  receives  sonoro 
impulses  through  the  medium  of  the  fluid  of  the  labyrinth  from 
the  cavity  of  the  vestibule,  and  from  the  fenestra  rotunda.  The 
lamina  spiralis  is,  indeed,  much  better  calculated  to  render  the 
action  of  these  undulations  upon  the  auditory  nerve  efficient, 
than  the  membranous  labyrinth  is:  for  as  a  solid  body  insulated 
by  a  different  medium,  it  is  capable  of  resonance. 

The  rods  of  Corti  are  probably  arranged  so  that  each  is  set  to 
vibrate  in  unison  with  a  particular  tone,  and  thus  strike  a  par- 
ticular note,  the  sensation  of  which  is  earned  to  the  brain  by  those 
filaments  of  the  auditory  nerve  with  which  the  little  vibrating  rod 
is  connected.  The  distinctive  function,  therefore,  of  these  minute 
bodies  is,  probably,  to  render  sensible  to  the  brain  the  various 
musical  notes  and  tones,  one  of  them  answering  to  one  tone,  and 
one  to  another  ;  while  perhaps  the  other  parts  of  the  organ  of 
hearing  discriminate  between  the  intensities  of  different  sounds, 
rather  than  their  qualities. 

"  In  the  cochlea  we  have  to  do  with  a  series  of  apparatus 
adapted  for  performing  sympathetic  vibrations  with  wonderful 
exactness.  We  have  here  before  us  a  musical  instrument  which 
is  designed,  not  to  create  musical  sounds,  but  to  render  them 
perceptible,  and  which  is  similar  in  construction  to  artificial 
musical  instruments,  but  which  far  surpasses  them  in  the  delicacy 
as  well  as  the  simplicity  of  its  execution.  For,  while  in  a  piano 
every  string  must  have  a  separate  hammer  by  means  of  which  it 
is  sounded,  the  ear  possesses  a  single  hammer  of  an  ingenious 
form  in  its  ear-bones,  which  can  make  every  string  of  the  organ  of 
Corti  sound  separately."     (Bernstein.) 


About  3000  rods  of  Corti  are  present  in  the  human  ear  ;  this  would  give 
about  400  to  each  of  the  seven  octaves  which  are  within  the  compass  of  the 
ear.  Thus  about  32  would  go  to  each  semi-f  one.  Weber  asserts  that  accom- 
plished musicians  can  appreciate  differences  in  pitch  as  small  as  Jjth  of  a 
tone.  Thus  on  the  theory  above  advanced,  the  delicacy  of  discrimination 
would,  in  this  case,  appear  to  have  reached  its  limits. 


6S8  THE    SENSES.  [chap.  xix. 

Sensibility  of  the  Auditory  Nerve. — Any  elastic  body,  e.g., 
air,  a  membrane,  or  a  string  performing  a  certain  number  of  regular 
vibrations  in  the  second,  gives  rise  to  what  is  termed  a  musical 
sound  or  tone.  We  must,  however,  distinguish  between  a  musical 
•sound  and  a  mere  noise ;  the  latter  being  due  to  irregular  vibra- 
tions. 

Qualities  of  Musical  Sound. — Musical  sounds  are  distin- 
guished from  each  other  by  three  qualities,  i.  Strength  or  inten- 
sity, which  is  due  to  the  amplitude  or  length  of  the  vibrations. 

2.  Pitch,  which  depends  upon  the  number  of  vibrations  in  a  second. 

3.  Quality,  Colour,  or  Timbre.  It  is  by  this  property  that  we  dis- 
tinguish the  same  note  sounded  on  two  instruments,  e.g.,  a  piano 
•and  a  flute.  It  has  been  proved  by  Helmholtz  to  depend  on  the 
number  of  secondary  notes,  termed  harmonics,  which  are  present 
with  the  predominating  or  fundamental  tone. 

It  would  appear  that  two  impulses,  which  are  equivalent  to  four  single  or 
lialf  vibrations,  are  sufficient  to  produce  a  definite  note,  audible  as  such 
through  the  auditory  nerve.  The  note  produced  by  the  shocks  of  the  teeth 
of  a  revolving  wheel,  at  regular  intervals  upon  a  solid  body,  is  still  heard 
when  the  teeth  of  the  wheel  are  removed  in  succession,  until  two  only  are 
left  ;  the  second  produced  by  the  impulse  of  these  two  teeth  has  still  the 
ame  definite  value  in  the  scale  of  music. 

The  maximum  and  minimum  of  the  intervals  of  successive  impulses  still 
appreciable  through  the  auditory  nerve  as  determinate  sounds,  have  been 
determined  by  M.  Savart.  If  their  intensity  is  sufficiently  great,  sounds  are 
still  audible  which  result  from  the  succession  of  48.000  half  vibrations,  or 
24.000  impulses  in  a  second  ;  and  this,  probably,  is  not  the  extreme  limit  in 
acuteness  of  sounds  perceptible  by  the  ear.  For  the  opposite  extreme,  he 
has  succeeded  in  rendering  sounds  audible  which  were  produced  by  only 
fourteen  or  eighteen  half  vibrations,  or  seven  or  eight  impulses  in  a  second  ; 
and  sounds  still  deeper  might  probably  be  heard,  if  the  individual  impulses 
could  be  sufficiently  prolonged 

By  removing  one  or  several  teeth  from  the  toothed  wheel 
the  fact  has  been  demonstrated  that  in  the  case  of  the  auditory 
nerve,  as  in  that  of  the  optic  nerve,  the  sensation  continues  longer 
than  the  impression  which  causes  it ;  for  a  removal  of  a  tooth  from 
the  wheel  produced  no  interruption  of  the  sound.  The  gradual 
cessation  of  the  sensation  of  sound  renders  it  difficult,  however,  to 
determine  its  exact  duration  beyond  that  of  the  impression  of  the 
sonorous  impulses. 

Direction  of  Sounds. — The  power  of  perceiving  the  direction  of 


chap,  xix.]  MUSICAL  SOUND.  689 

sounds  is  not  :i  faculty  of  the  sense  of  bearing  itself,  but  is  an 
act  of  the  mind  judging  on  experience  previously  acquired. 
From    the    modifications   which    the  sensation   of  sound    under- 

ea  according  to  the  direction  in  which  the  sound  reaches 
os,  the  mind  infers  the  position  of  the  sounding  body.  The 
only  true  guide  for  this  inference  is  the  more  intense  action 
of  the  sound  upon  one  than  upon  the  other  ear.  But  even 
here  there  is  room  for  much  deception,  by  the  influence 
of  reflexion  or  resonance,  and  by  the  propagation  of  sound 
from  a  distance,  without  loss  of  intensity,  through  curved  con- 
ducting tubes  filled  with  air.  By  means  of  such  tubes,  or  of  solid 
.  inductors,  which  convey  the  sonorous  vibrations  from  their  source 
to  a  distant  resonant  body,  sounds  may  be  made  to  appear  to 
originate  in  a  new  situation.  The  direction  of  sound  may  also  be 
judged  of  by  means  of  one  ear  only ;  the  position  of  the  ear  and 
I  lead  being  varied,  so  that  the  sonorous  undulations  at  one'moment 
fall  upon  the  ear  in  a  perpendicular  direction,  at  another  moment 
obliquely.  But  when  neither  of  these  circumstances  can  guide  us 
in  distinguishing  the  direction  of  sound,  as  when  it  falls  equally 
upon  both  ears,  its  source  being,  for  example,  either  directly  in 
front  or  behind  us,  it  becomes  impossible  to  determine  whence  the 
sound  comes. 

Distance  of  Sounds. — The  distance  of  the  source  of  sounds  is 
not  recognized  by  the  sense  itself,  but  is  inferred  from  their  in- 
tensity. The  sound  itself  is  always  seated  but  in  one  place, 
namely,  in  our  ear ;  but  it  is  interpreted  as  coming  from  an  ex- 
terior soniferous  body.  When  the  intensity  of  the  voice  is  modi- 
tied  in  imitation  of  the  effect  of  distance,  it  excites  the  idea  of 
its  originating  at  a  distance.  Ventriloquists  take  advantage  of 
the  difficulty  with  which  the  direction  of  sound  is  recognized,  and 
jdso  the  influence  of  the  imagination  over  our  judgment,  when 
they  direct  their  voice  in  a  certain  direction,  and  at 'the  same 
time  pretend,  themselves,  to  hear  the  sounds]  as_[coming  from 
thence. 

The  effect  of  the  action  of  sonorous  undulations  upon  the  nerve 
of  hearing,  endures  somewhat  longer  than  the  period  during  which 
the  undulations  are  passing  [through  the  ear.  If,  however,  the 
impressions  of  the  same  sound  be  very  long  continued,  or  con- 
stantly repeated  for  a  long  time,  then  the  sensation  produced  may 

Y  Y 


6q0  THE   SEXSES.  [chap.  xix. 

continue  for  a   very  Ion g  time,  more  than  twelve  or  twenty-four 
hours  even,  after  the  original  cause  of  the  sound  lias  ceased. 

Binaural  Sensations. — Corresponding  to  the  double  vision  of 
the  same  object  with  the  two  eyes,  is  the  double  hearing  with  the 
two  oars  :  and  analogous  to  the  double  vision  with  one  eye,  de- 
pendent on  unequal  refraction,  is  the  double  hearing  of  a  single 
sound  with  one  ear,  owing  to  the  sound  coming  to  the  ear  through 
media  of  unequal  conducting  power.  The  first  kind  of  double 
hearing  is  very  rare  :  instances  of  it  are  recorded,  however,  by 
Sauvages  and  Itard.  The  second  kind,  which  depends  on  the 
unequal  conducting  power  of  two  media  through  which  the  same 
sound  is  transmitted  to  the  ear,  may  easily  lie  experienced.  If  a 
small  bell  be  sounded  in  water,  while  the  ears  are  closed  by  plugs, 
and  a  solid  conductor  be  interposed  between  the  water  and  the 
ear,  two  sounds  will  be  heard  differing  in  intensity  and  tone  ;  <>ne 
being  conveved  to  the  ear  through  the  medium  of  the  atmosphere, 
the  other  through  the  conducting-rod. 

Subjective  Sensations  of  Sound. — Subjective  sounds  are  the 
result  of  a  state  of  irritation  or  excitement  of  the  auditory  nerve 
produced  by  other  causes  than  sonorous  impulses.  A  state  of  excite- 
ment of  this  nerve,  however  induced,  gives  rise  to  the  sensation  of 
sound.  Hence  the  ringing  and  buzzing  in  the  ears  heard  1  >y  persons 
of  irritable  and  exhausted  nervous  system,  and  by  patients  with 
cerebral  disease,  or  disease  of  the  auditory  nerve  itself ;  hence  also 
the  noise  in  the  ears  heard  for  some  time  after  a  long  journey  in  a 
rattling  noisy  vehicle.  Ritter  found  that  electricity  also  excites  a 
sound  in  the  ears.  From  the  above  truly  subjective  sound  we 
must  distinguish  those  dependent,  not  en  a  state  of  the  auditory 
nerve  itself  merely,  but  on  sonorous  vibrations  excited  in  the  audi- 
t  rv  apparatus.  Such  are  the  buzzing  sounds  attendant  on  vas- 
cular congestion  of  the  head  and  ear,  or  on  aneurismal  dilatation 
of  the  vessels.  Frequently  even  the  simple  pulsatory  circulation 
ot  the  blood  in  the  ear  is  heard.  To  the  sounds  of  this  class  belong 
also  the  buzz  or  hum  heard  during  the  contraction  of  the  palatine 
muscles  in  the  act  of  yawning ;  during  the  forcing  of  air  into  the 
tympanum,  so  as  make  tense  the  membrana  tynrpani ;  and  in  the 
act  of  blowing  the  nose,  as  well  during  the  forcible  depression  of 
the  lower  jaw. 

Irritation  or    excitement  of   the    auditorv  nerve  is  capable  of 


(  b  u\  xr\.]  SIGHT.  691 

riving  rise  to  movements  in  the   body,  and  to  sensations  in  other 

■ 

is  of  sense.     In   !■  *   La  probable  that  tlie  laws 

action,  through  the   medium  of  tie-  brain,  came  into  play. 
An  ;  ind  sudden  noise  excites,  in  every  person,  closui 

tlie  eyelids,  and,  in  nervous  individuals,  a  start  of  the  whole 
body  or  an  unpleasant  sensation,  like  that  produced  by  an  electric 
shock,  throughout  the  body,  and  sometimes  a  particular  feeling 
in  the  external  ear.  Various  Bounds  cause  in  many  people  a 
_:veal>le  feeling  in  the  teeth,  or  a  sensation  of  cold  tickling 
through  tlie  body,  and,  in  some  people,  intense  Bounds  are  said  to 
liva  collect. 

Sight. 

Eyelids  and  Lachrymal  Apparatus. — The  eyelids  consist 
of  two  movable  folds  of  skin,  each  of  which  is  kept  in  shape  by  a 
thin  plate  of  yellow  clastic  tissue.  Along  their  free  edges  are 
ted  a  number  of  curved  hairs  (eyelashes),  which,  when  the  lids 
are  half  closed,  serve  to  protect  the  eye  from  dust  and  other  for  _ 
bodies  :  their  tactile  sensibility  is  also  very  delicate. 

On  the  inner  surface  of  the  elastic  tissue  are  disposed  a 
number  of  small  racemose  glands  (Meibomian),  whose  ducts  open 
near  the  free  edge  of  the  lid. 

The  orbital  surface  of  each  lid  is  lined  by  a  delicate,  highly 
sensitive  mucous  membrane  (conjunctiva),  which  is  continuous 
with  the  skin  at  the  free  edge  of  each  lid,  and  after  lining  the 
inner  surface  of  the  eyelid  is  reflected  on  to  the  eyeball,  being 
somewhat  loosely  adherent  to  the  sclerotic  coat.  The  epithelial 
layer  is  c<  >ntinued  over  the  cornea  at  its  anterior  epithelium.  At 
the  inner  edge  of  the  eye  the  conjunctiva  becomes  continuous 
with  the  mucous  lining  of  the  lachrymal  sac  and  duct,  which 
again  is  continuous  with  the  mucous  membrane  of  the  inferior 
meatus  of  the  nose. 

The  lachrymal  gland  is  lodged  in  the  upper  and  outer  angle  of 
the  orbit.  Its  secretion,  which  issues  from  several  ducts  on  the 
inner  surface  of  the  upper  lid,  under  ordinary  circumstances  just 
suffices  to  keep  the  conjunctiva  moist.  It  passes  out  through  two 
small  openings  (puncta  lachrymalia)  near  the  inner  angle  of  the 
eye,  one  in  each  lid,  into  the  lachrymal  sac,  and  thence  along  the 
nasal  duct  into  the  inferior  meatus  of  the  nose      The  excessive 

T   Y   2 


6g: 


SENSE   OF   SIGHT 


[chap,  xix 


secretion  poured  out  under  the  influence  of  any  irritating  vapour 
or  painful  emotion  overflows  the  lower  lid  in  the  form  of  tears. 

The  eyelids  are  closed  by  the  contraction  of  a  sphincter  muscle 
(orbicularis),  supplied  by  the  Facial  nerve ;  the  upper  lid  is  raised 
by  the  Levator  palpebra  superioris,  which  is  supplied  by  the  Third 
nerve. 

The  Eyeball. 

The  eyeball  or  the  organ  of  vision  (fig.  365)  consists  of  a  variety 
of  structures  which  may  be  thus  enumerated : — 

The  sclerotic,  or  outermost  coat,  envelops  about  five-sixths  of 
the  eyeball :  continuous  with  it,   in  front,  and  occupying  the  re- 


-Sclerotic  coat 
-Choroid  coat 
-Ketina 


Miliary  muscle- 
Ciliary  process- 
Canal  of  Petit- 
Cornea- 

Autcrior  chamber- 
Lens- 

Iris- 
Ciliary  process- 
Ciliary  muscle- 


-Vitreous 
humour 


\  Fig.  365. 

maining  sixth  is  the  cornea.  Immediately  within  the  sclerotic  is 
the  choroid  coat,  and  within  the  choroid  is  the  retina.  The  interior 
of  the  eyeball  is  well-nigh  filled  by  the  aqueous  and  vitreous  humours 
and  the  crystalline  lens;  but,  also,  there  is  suspended  in  the 
interior  a  contractile  and  perforated  curtain, — the  iris,  for  regu- 
lating the  admission  of  light,  and  behind  the  junction  of  the 
sclerotic  and  cornea  is  a  ciliary  muscle,  the  function  of  which  is 
to  adapt  the  eye  for  seeing  objects  at  various  distances. 

Structure  of  Sclerotic. — The  sclerotic  coat  is  composed  of  con- 
nective tissue,  arranged  in  variously  disposed  and  inter-communi- 


ill  LP.   XIX.] 


STB1  «   i  IKK   OF    I  OBNEA. 


^93 


eating   layers.     It   La   Btrong,   tough,  and  opaque,  and  Dot  very 
alastio. 

Structure  of  Cornea. — The  cornea  is  .1  transparent  membrane 
which  forms   ;i  segment  of  a  smaller 
sphere  than  the  rest  of  the  eyeball,  and 

is  let  in,  as  it  were,  into  the  sclerotic 

with  which  it  is  continuous  all  round. 

coated  with  a  Laminated  anterior 

epithelium    (a,  fig.   367)  consisting   of 

seven  <>r  eight  layers  of  cells,  of  which 
the  superficial  ones  are  flattened  am! 
scaly,  and  the  deeper  ones  more  or  less 
columnar.  Immediately  beneath  this 
is  the  anterior  elastic  lamina  (Bowman). 

The  cornea  tissue  proper  as  well  ;i> 
its  epithelium  is,  in  the  adult,  com- 
pletely destitute  of  blood-vessels ;  it 
consists  of  an  intercellular  ground-sub- 
stance of  rather  obscurely  fibrillated 
flattened  bundles  of  connective  tissue, 
arranged  parallel  to  the  free  surface, 
and  forming  the  boundaries  of  branched 
anastomosing  spaces  in  which  the  cornea- 
corpuscles  lie.  These  branched  cornea  - 
corpuscles  have  been  seen  to  creep  by 
amoeboid  movement  from  one  branched 
space  into  another.  At  its  posterior 
surface  the  cornea  is  limited  by  the 
posterior  elastic  lamina,  or  membrane 
of  Descemet,  the  inner  layer  of  which 
jists  of  a  single  stratum  of  epithelial 
cells  (fig.  366,  d). 

Nerves  of  Cornea. — The  nerves  of 
the  cornea  are  both  large  and  numer- 
ous :  they  are  derived  from  the  ciliary 


.  _  j66. —  Vertical  section  of  rab- 
bits cornea,  stained  with  gold 
(•hloride.  e,  Laminated  ante- 
rior epithelium.  Immediately 
beneath  this  is  the  anterior 
elastic  lamina  of  Bowman. 
t?,  Nerves  forming  a  delicate 
sub  -  epithelial  plexus,  and 
sending  up  fine  twigs  between 
the  epithelial  cells  to  end  in  a 
second  plexus  on  the  free 
surface  ;  </,  Descemet's  mem- 
brane, consisting  of  a  fine 
elastic  layer,  and  a  single 
layer  of  epithelial  cells ;  the 
substance  of  the  cornea,/,  is 
seen  tub'-  tibrillated,  and  con- 
tains many  layers  of  branched 
cospnacles,  arranged  parallel 
to  the  free  surface,  and  here 
seen  edgewise.     (Schofield.) 


nerves.    They  traverse  the  substance  of 
the  cornea,  in  which  some  of  them  ter- 
minate, in  the  direction  of  its  anterior  surface,  near  which  the  axis 
cylinders  break  up  into  bundles  of  very  delicate  beaded  fibrillar 


694 


SENSE   OF   SIGHT. 


[(HAP.   XIX. 


(fig.  366)  :  these  form  a  plexus  immediately  beneath  the  epithe- 
lium, from  which  delicate  fibrils  pass  up  between  the  cells  anas- 


x-,  i  W^MMmm 


Fig.  367. — Vertical  section  of  rabbit's  cornea,  a,  Anterior  epithelium,  showing  the  different 
shapes  of  the  cells  at  various  depths  from  the  free  surface  ;  b,  portion  of  the  substance 
of  cornea.     (Klein.) 

tomosing  with  horizontal  branches,  and  forming  a  deep  intra- 
epithelial plexus,  from  which  fibres  ascend,  till  near  the  surface 
they  form  a  superficial  intra-epithelial  net-work. 


N 


Fig.  368. — Horizontal  preparation  of  cornea  of  frog ;   showing  the  network  of  branched 
cornea  corpuscles.    The  ground  substance  is  completely  colourless,     x  400.     (Klein.) 

Structure  of  Choroid  (tunica  vasculosa). — This  coat  of  the 
eye-ball  is  formed  by  a  very  rich  network  of  capillaries  (chorio- 
capillaris)  outside  which  again  are  connective-tissue  layers  of  stellate 
pigmented  cells  (fig.  25)  with  numerous  arteries  and  veins. 

The  choroid  coat  ends  in  front  in  what  are  called  the  ciliary 
'processes  (fig.  365). 

Structure  of  Retina. — The  retina  (fig.  370)  is  a  delicate  mem- 


CHAP.   \  i\.  ] 


STRUCTURE  OF   RETINA. 


695 


Fig.  369. — Surface  view  of  part  of  lamella  of  kitten's  cornea,  pre- 
pared first  -with  caustic  potash  and  then  with  nitrate  of 
silver.  By  this  method  the  branched  cornea-corpuscles 
with  their  granular  protoplasm  and  large  oval  nuclei  are 
brought  out.)     x  450.     ( Klein  and  Noble  Smith.) 


brane,  concave,  with  the  concavity  directed  forwards  and  ending 
in  front,  Dear  the  outer  pari  of  the  ciliary  processes  in  a  finely 
notched  edge, — the  ora  serrata.  Semi-transparent  when  fresh,  it 
boob  becomes  clouded  and  opaque,  with  a  pinkish  tint  from  the 
Mood  in  its  minute  vessels.     It  results  from  the  sudden  spreading 

Out  or  expansion 
of  the  optic  nerve, 
of  whose  terminal 
fibres,  apparently 
deprived  of  their 
external  whitesub- 
stance,  together 
with  nerve  cells, 
it  is  essentially 
composed. 

Exactly  in  the 
centre  of  the  re- 
tina, and  at  a 
point  thus  cor- 
responding to  the  axis  of  the  eye  in  which  the  sense  of  vision  is 
most  perfect,  is  a  round  yellowish  elevated  spot,  about  -^  of  an 
inch  in  diameter,  having  a  minute  aperture  at  its  summit,  and 
called  after  its  discoverer  the  yellow  spot  of  Soemmering.  In  its  centre 
is  a  minute  depression  called  fovea  centralis.  About  T\  of  an  inch 
to  the  inner  side  of  the  yellow  spot,  and  consequently  of  the  axis 
of  the  eye,  is  the  point  at  which  the  optic  nerve  begins  to  spread 
out  its  fibres  to  form  the  retina.  This  is  the  only  point  of  the 
surface  of  the  retina  from  which  the  power  of  vision  is  absent. 

The  retina  consists  of  certain  nervous  elements  arranged  in 
several  layers,  and  supported  by  a  very  delicate  connective  tissue. 

From  the  nature  of  the  case  there  is  still  considerable  uncer- 
tainty as  to  the  character  (nervous  or  connective  tissue)  of  some 
of  the  layers  of  the  retina.  The  following  ten  layers,  from  within 
outwards,  are  usually  to  be  distinguished  in  a  vertical  section 
(figs.  370,  373). 

1.  Membrana  limitam  interna:  a  delicate  membrane  in  contact 
with  the  vitreous  humour. 

2.  Fibres  of  optic  nerve.  This  layer  is  of  very  varying  thickness  in 
different  parts  of  the  retina  :  it  consists  chiefly  of  non-medullated 


6g6 


SEXSE   OF   SIGHT. 


[CH  VI'.   XIX 


fibres  which  interlace,  and  some  of  which  are  continuous  with  pro- 
cesses of  the  large  nerve-cells  forming  the  next  layer. 

3.  Layer  of  ganglionic  corpuscles,  consisting  of  large  multipolar 
nerve-cells,  sometimes  forming  a  single  layer.     In  some  parts  of 

the  retina,  especially  near  the 
macula  lutea,  this  layer  is  very 
thick,  consisting  of  several  distinct, 
strata  of  nerve-cells.  These  cells 
lie  in  the  spaces  of  a  connective- 
tissue  framework. 

4.  Molecular  layer.  This  presents 
a  finely  granulated  appearance.  It 
consists  of  a  punctiform  connective 
tissue  traversed  by  numberless  very 
fine  fibrillar  processes  of  the  nerve- 
cells. 

5.  Internal  granular  layer.  This 
consists  chiefly  of  numerous  small 
round  cells  with  a  very  small  quan- 
tity of  protoplasm  surrounding  a 
large  nucleus  ;  they  are  generally 
bipolar,  giving  off  one  process  out- 
wards and  another  inwards.  They 
greatly  resemble  the  ganglionic- 
corpuscles  of  the  cerebellum  (fig.. 
330).  Besides  these  there  are  large 
oval  nuclei  (e,  fig.  370,  A)  belonging 
to  the  sustentacular  connective 
tissue  fibres. 

6.  Intergranular  layer;  which 
closely  resembles  the  molecular  layer 
but  is  much  thinner.  It  con- 
sists of  finely-dotted  connective 
tissue  with  nerve  fibrils. 

7.  External  granular  layer  ;  which  consists  of  several  strata  of 
small  cells  resembling  those  of  the  internal  granular  layer  ;  they 
have  been  classed  as  rod  and  cone  granules,  according  as  they  are 
connected  by  very  delicate  fibrils  with  the  rods  and  cones 
respectively.     They  are  lodged  in    the    meshes  of    a    connective. 


Pig.  370. — Diagram  of  the  retina.  A, 
connective  tissue  portion  ;  B,  nervous 
portion  ;  (the  two  must  be  combined  t>i 
form  the  complete  retina  ;)  a  a,  mem- 
brana  limitans  externa  ;  b,  rods  ;  c , 
cones ;  b'.  rod-granule  ;  c',  cone-gra- 
nule ;  both  belonging  to  the  external 
granule  layer;  e,  Miiller's  sustenta- 
cular fibres,  with  their  nuclei  e  ; 
d ,  intergranular  layer ;  /,  internal 
granule  layer ;  g,  molecular  layer, 
connective-tissue  portion  ;  </',  mole- 
cular layer,  nerve-fibril  portion ; 
h,  ganglion  cells ;  h',  their  axis-cylin- 
der process ;  1",  nerve-fibre  layer. 
(Max  Schultze.) 


CHAP.    XIX.];' 


STRUCTURE  OF    RETINA. 


697 


Fig.  371. — Ciliary  processes,  as  seen  from 
behind.  1,  posterior  surface  of  the  iris,, 
•with  the  sphincter  muscle  of  the  pupil  ; 

2,  anterior  part    of    the  choroid   coat :. 

3,  one  of  the  ciliary  processes,  of  which, 
about  seventy  are  represented,      h. 


tissue  framework.      Both    the   internal  and  externa]  granular  layer 
stain  very    rapidly   and    deeply  with    hematoxylin,    while   the    roe!) 

and  cone   layer    remains    quite 

unstained. 

8.  Membrana  limitans  externa  ; 
a  delicate,  well-defined  membrane, 
dearly  marking  the  internal 
limit   of  the  rod   and  cone  layer. 

9.  Hod  and  rone  layer,  badllar 
layer,    or    membrane    of   Jacob, 
consisting   of  two   kinds   of  ele- 
ments :    the   "  rods,"   which    are 
cylindrical   and   of  uniform  dia- 
meter    throughout,      and     the 
"  cones,"  whose  internal  portion 
is    distinctly    conical,    and    sur- 
mounted   externally  by    a   thin 
rod-like   body.       According 
to    the    researches    of   Max 
Schultze,    the     rods    show 
traces  of  longitudinal  fibril- 
lation, and,  moreover,  have 
a  great  tendency  to  break  up 
into  a  number  of  transverse 
discs  like  a  pile  of  coins. 

In  the  rod  and  cone  layer 
of  birds,  the  cones  usually 
predominate  largely  in  num- 
ber, whereas  in  man  the 
rods  are  by  far  the  more 
numerous.  In  nocturnal 
birds,  however,  such  as  the 
owl,  only  rods  are  present, 
and  the  same  appears  to  be 
the  case  in  many  nocturnal 
and  burrowing  mammalia. 
e.g.,  bat,  hedge-hog,  mouse, 


Fig.  372. — The  posterior  half  of  the  retina  of  the  left 
1  v< ',  viewed  from  before ;  s,  the  cut  edge  of  the 
sclerotic,  coat ;  ck,  the  choroid  ;  r,  the  retina ; 
in  the  interior  at  the  middle,  the  macula  lutea 
■with  the  depression  of  the  fovea  centralis  is 
represented  by  a  slight  oval  shade;  towards 
the  left  side  the  light  spot  indicates  the  colli- 
culus  or  eminence  at  the  entrance  of  the  optic 
nerve,  from  the  centre  of  which  the  arteria 
centralis  is  seen  spreading  its  branches  into 
the  retina,  leaving  the  part  occupied  by  the 
macula  comparatively  free.     (After  Henle.) 


and  mole- 

10.  Pigment  eel!  layer,  which  was  formerly  considered  part  of 
the  choroid. 


69S 


SEXSE   OF   SIGHT. 


[(  BAP.   XIX. 


• 


In  the  centre  of  the  yellew  spot  (macula  lutea),  all  the  layers  of 
the    retina    become    greatly  thinned    out    and    almost   disappear, 

except  the  rod  and  cone 
layer,  which  considerably 

increases  in  thickness, 
and  comes  to  consist 
almost  entirely  of  long 
slender  cones,  the  rods 
being  very  few  in  num- 
ber, or  entirely  absent. 
There  are  capillar]  - 
here,  but  none  of  the 
larger  branches  of  the 
retinal  arteries. 


With  regard  to  the  con- 
nection of  the  various  layers 
there  is  still  some  uncer- 
tainty.. Fig.  370  represents 
the  view  of  Max  Sehultze. 
According  to  this  there  are 
certain  sustentacular  fibres 
of  connective  tissue  (radiat- 
ing fibres  of  Miiller)  which 
spring  from  the  membrana 
limitans  interna  almost  ver- 
tically, and  traverse  the  re- 
tina to  the  limitans  externa, 
whence  very  delicate  con- 
nective tissue  processes  pass 
up  between  the  rods  and 
cones.  The  framework  which 
form  is  represented  in 
fig.  370.  A.  The  nervous 
elements  of  the  retina  are 
represented  in  fig.  370.  B. 
and  consist  of  delicate  fibres 
passing  up  from  the  nerve-fibre  layer  to  the  rods  and  cones,  and  connected 
with  the  ganglionic  corpus  -  1  granules  of  the  internal  and  external 
layer. 

Blooci -vessels  of  the  Eyeball. — The  eye  is  very  richly  sup- 
plied witli  blood-vessels.  In  addition  to  the  conjunctival  vessels 
which  are  derived  from  the  palpebral  and  lachrymal  arteries, 
there  are  at  least  two  other  distinct  sets  of  vessels  supplying  the 
tunics  of  the  eyeball.  (1  )  The  vessels  of  the  sclerotic,  choroid, 
and  iris,  and  (2)  The  vessels  of  the  retina. 


Fig.  373- — - 

sclerotic,  moderately  magnified.  «.  membrana 
limitans  interna ;  b ,  nerve-fibre  layer  traversed 
by  Miiller' s  sustentacular  fibres  of  the  connec- 
tive tissue  system  :  c,  ganglion-cell  layer :  d, 
molecular  layer :  e,  interna]  granular  layer  ; 
/,  intergranular  layer;  g,  external  granular 
layer  ;  ft,  membrana  limitans  externa,  running 
along  the  lower  part  of  i.  the  layer  of  rods  and 
cones ;  /.-.  pigment  cell  layer  formerly  described 
as  part  of  the  choroid  :  I,  m,  internal  and  external 
vascular  portions  of  the  choroid,  the  first  con- 
taining capillaries,  the  second  larger  blood-ves- 
sels, cut  in  transverse  section  ;  n,  sclerotic.  W. 
Pye. 


x.J  [<  Al.  APPARATUS.  699 

iary  arteries  whi 
icin  tl.  .eball,  and  the  n  iliary 

which  enter  near  the  insert]  he  reeti.  ■  and 

form  a  very  rich  choroidal  plexus  ;  they  nd  ciliary  pro- 

cesses, ighly  vascnlar  circle  round  the  outer  margin  of  the 

-  and  adjoii  thee        >tic 

1    —els  fn>m   those   of  the  conjunctiva   is  well 
seen  in  tl.  ice  between  the  bright  re<l  of  blood-shot  junc- 

tival  :ul  the  pink  zone  surrounding  the  cornea  which  indicates 

<1  ciliary  conges' 
(2.)   1;.  \  retinal  fig.  572)  are  derived  from  the  arteria  centralis 

hich  enters  the  eyeball  along  the  centre  of  the  optic  nerve, 
rami;  t  the  retina,  chiefly  in  its  inner  layers.     They  can  be  seen  by 

direct  ophthalmoscopic  examination. 


Optical  Apparatus. 

The  eye  may  he  compared  to  the  cam*         -    1  by  photographers 
formed  by  a  convex  lens.     In  this   ins!  t  im  ges  of  external 

objects  are  thrown  upon  _:  l-gl  88  -  1  :en  at  the  back  of  a 
box,  the  interior  of  which  is  painted  black.  In  the  eve  the  convex 
lens  is  re]      -  •*  the  crystalline  lens,  the  dark  box  by  the 

.-ball  with  its  _      nt,  and  -        -   reen  by  the  retina. 

In  the       -      "  I  jnera  the  sci     a  is     oabled  to  receive  clear 

images  of  ts  at  different  being   shifted  forward 

and  back  :  whil     1  vex  lens  too  can  be  screwed  in  and  out. 

The  corresponding       ntrivance  in  the  ibed  under 

the  head  of  Accovum 

Conditions    Necessary. — The      asential   constituents  of  the 

eye  may  be    thus    enumerated  :    (1)  A 
hire  (the  retina     *  stimulated  by  light  and 

trans     it  -     f  the      ptic  nerve.  <>f  which  it  is  the  terminal 

expansion,  the  in.       ssi  th      stimulation    to    the    brain,  in 

which  it  excites  tl      sensatioi  ;  (2  >n- 

sisl     _  in  refra  tory  media,  .        stalline  lens,  aqu€ 

-,  the  function  of  whi  to  collecl  (   _  :her 

into  one  pointy  the  different  diverg  nf        -   emitted  1  point 

of  every  external  bod  _        _  then  l  &  tions  that 

they  are   exactly  :  tina,  and  thus  produce  an 

exact  imag         I  I  I  I  eed.     F        a     _ 

radiates  from  a  luminous  body  in  all  hen  the  media 

fer  no    impediment  to  its  trans  a,   a   luminous  point  will 

necessarily  illuminate  all       rts  -   if  ace,  such 

ingle  point.     A  retina,  there- 


•JOO  SENSE   OF   SIGHT.  [chap.  xix. 

fore,  without  any  optical  apparatus  placed  in  front  of  it  to  sepa- 
rate the  light  of  different  objects,  would  not  allow  of  distinct 
vision,  but  would  merely  transmit  such  a  general  impression  of 
daylight  as  Avould  distinguish  it  from  the  night  ;  (3)  A  contractile 
diaphragm  (iris)  with  a  central  aperture  for  regulating  the  quantity 
of  light  admitted  into  the  eye  :  and  (4)  a  contractile  structure 
(ciliary  muscle),  an  arrangement  by  which  the  chief  refracting 
medium  (crystalline  lens)  shall  be  so  controlled  as  to  enable  object* 
to  be  seen  at  various  distances,  causing  convergence  of  the  rays  of 
light  that  fall  upon  and  traverse  it  (accommodation). 

Refracting  Media. 

Of  the  refracting  media  the  cornea  is  in  a  twofold  manner  capable 
of  refracting  and  causing  convergence  of  the  rays  of  light  that  fall 
upon  and  traverse  it.  It  thus  affects  them  first,  by  its  density ; 
for  it  is  a  law  in  optics  that  when  rays  of  light  pass  from  a 
rarer  into  a  denser  medium,  if  they  impinge  upon  the  surface 
in  a  direction  removed  from  the  perpendicular,  they  are  bent  out 
of  their  former  direction  towards  that  of  a  line  perpendicular  to 
the  surface  of  the  denser  medium  ;  and,  secondly,  by  its  con- 
vexity ;  since  rays  of  light  impinging  upon  a  convex  transparent 
surface,  are  refracted  towards  the  centre,  those  being  most 
refracted  which  are  farthest  from  the  centre  of  the  convex  surface. 

Behind  the  cornea  is  a  space  containing  ;t  thin  watery  fluid, 
the  aqueous  humour,  holding  in  solution  a  small  quantity  of 
sodium  chloride  and  extractive  matter.  The  space  containing  the 
aqueous  humour  is  divided  into  an  anterior  and  posterior  chamber 
by  a  membranous  partition,  the  iris,  to  be  presently  again  men- 
tioned. The  effect  produced  by  the  aqueous  humour  on  the  rays 
of  light  traversing  it,  is  not  yet  fully  ascertained.  Its  chief  use, 
probably,  is  to  assist  in  filling  the  eyeball,  so  as  to  maintain  its 
proper  convexity,  and  at  the  same  time  to  furnish  a  medium  in 
which  the  movements  of  the  iris  can  take  place. 

Behind  the  aqueous  humour  and  the  iris,  and  imbedded  in  the 
anterior  part  of  the  medium  next  to  be  described,  viz.,  the  vitreous 
humour,  is  seated  a  doubly-convex  body,  the  crystalline  lens,  which 
is  the  most  important  refracting  structure  of  the  eye.  The  struc- 
ture of  the  lens  is  very  complex.  It  consists  essentially  of  fibres 
united  side  by  side  to  each  other,  and  arranged  together  in  very 
numerous  laminae,  which  are  so  placed  upon    one   another,  that 


«  HAP.   XI X.J 


ACTION    OF    'I  UK    litis. 


/OI 


I  .  -4. — Laminated  structure  of 
fStaUine  lens.  The  laminte 
are  split  up  after  hardening  in 
alcohol.  1,  the  denser  central 
part  or  nucleus  ;  2,  the  successive 
external  layers .     \ .      Arnold . ) 


when  bardened  in  spirit  the  lens  splits  into  three  portions  in  t K<- 
form  <»t  .  each  of  which  is  composed  of  Buperimposed  con- 

centric Lamine.     The  lena  increases  in  density  and,  consequently, 
in  power  of  refraction,  from  without  inwards  ;  the  central  part, 
usually  termed  the  nucleus,  being  the 
most  dense. 

The     vitreous     humour    constitutes 
nearly  four-fifths  of  the  whole  globe  of 

the  eve.  It  fills  up  the  space  between 
the  retina  and  the  lens,  and  its  soft 
jelly-like  substance  consists  essentially 
of  numerous  layers,  formed  of  delicate, 
Bimple  membrane,  the  spaces  between 
which  are  filled  with  a  watery,  pellucid 
fluid.  Its  principal  use  appears  to  be 
that  of  giving  the  proper  distension 
to  the  globe  of  the  eye,  and  of  keeping 
the  surface  of  the  retina  at  a  proper 
distance  from  the  lens. 

Action  of  the  Iris. — The  iris  is  a  vertically-placed  mem- 
branous diaphragm,  provided  with  a  central  aperture,  the  pupil, 
for  the  transmission  of  light  It  is  composed  of  plain  muscular 
fibres  imbedded  in  ordinary  nbro-cellular  or  connective  tissue. 
The  muscular  fibres  have  a  direction,  for  the  most  part,  radiating 
from  the  circumference  towards  the  pupil ;  but  as  they  approach 
the  pupillary  margin,  they  assume  a  circular  direction,  and  at  the 
very  edge  form  a  complete  ring.  By  the  contraction  of  the 
radiating  fibres  (dilator  pupilke)  the  size  of  the  pupil  is  enlarged  : 
by  the  contraction  of  the  circular  ones  (sphincter  pupill&e).  it  is 
diminished.  The  object  effected  by  the  movements  of  the  iris,  is 
the  regulation  of  the  quantity  of  light  transmitted  to  the  retina. 
The  posterior  surface  of  the  iris  is  coated  with  a  layer  of  dark 
pigment,  so  that  no  rays  of  light  can  pass  to  the  retina,  except 
such  as  are  admitted  through  the  aperture  of  the  pupil. 

This  iris  is  very  richly  supplied  with  nerves  and  blood-vessels, 
its  circular  muscular  fibres  are  supplied  by  the  third  (by  the  short 
ciliary  branches  of  the  ophthalmic  ganglion),  and  its  radiating 
fibres,  by  the  sympathetic  and  fifth  cranial  nerve  (by  the  long 
ciliary  branches  of  the  nasal  nerve). 


702  SEX.SE   OF   SIGHT.  [chap.  xix. 

Contraction  of  the  pupil  occurs  under  the  following  cireum 
stances:  (i)  On  exposure  of  the  eye  to  a  bright  light  ;  (2)  when 
the  eye  is  focussed  for  near  objects  ;  (3 )  when  the  eyes  converge 
to  look  at  a  near  object ;  (4)  on  the  local  application  of  eserine 
(active  principle  of  Calabar  bean)  ;  (5)  on  the  administration  in 
ternally  of  opium,  aconite,  and  in  the  early  stages  of  chloroform 
and  alcohol  poisoning  ;  (6)  on  division  of  the  cervical  sympathetic 
or  stimulation  of  the  third  nerve.  Dilatation  of  the  pupil  occurs 
(1)  in  a  dim  light;  (2)  when  the  eye  is  focussed  for  distant 
objects  ;  (3)  on  the  local  application  of  atropine  and  its  allied  alka- 
loids ;  (4)  on  the  internal  administration  of  atropine  and  its  allies  ; 
(5)  in  the  later  stages  of  poisoning  by  chloroform,  opium,  and  other 
drugs  ;  (6)  on  paralysis  of  the  third  nerve  ;  (7)011  stimulation  of 
the  cervical  sympathetic,  or  of  its  centre  in  the  floor  of  the  front  of 
the  aqueduct  of  Sylvius.  The  contraction  of  the  pupil  appears  to 
be  under  the  control  of  a  centre  in  the  corpora  quadrigemina,  and 
this  is  reflexly  stimulated  by  a  bright  light,  and  the  dilatation  when 
the  reflex  centre  is  not  in  action  is  due  to  the  more  powerful 
sympathetic  action  ;  but  in  addition,  it  appears  that  both  con- 
traction and  dilatation  may  be  produced  by  a  local  mechanism, 
upon  which  certain  drugs  can  act,  which  is  independent  of  and 
probably  often  antagonistic  to  the  action  of  the  central  apparatus 
of  the  third  and  sympathetic  nerves.  The  action  of  the  fifth  nerve 
upon  the  pupil  is  not  well  understood,  but  its  apparent  effect  in 
producing  dilatation  is  due  to  the  mixture  of  sympathetic  fibres 
with  its  nasal  branch.  The  sympathetic  influence  upon  the 
radiating  fibres  is  believed  to  be  conveyed  not  by  the  long  ciliary 
branches  of  that  nerve,  but  by  the  short  ciliary  branches  from  the 
ophthalmic  ganglion. 

The  close  sympathy  subsisting  between  the  two  eyes  is  nowhere 
better  shown  than  by  the  condition  of  the  pupil.  If  one  eye  be 
shaded  by  the  hand  its  pupil  will  of  course  dilate  ;  but  the  pupil 
of  the  other  eye  will  also  dilate,  though  it  is  unshaded. 

Ciliary  Muscle. — The  ciliary  muscle  is  composed  of  plain 
muscular  fibres,  which  form  a  narrow  zone  around  the  interior  of 
the  eyeball,  near  the  line  of  junction  of  the  cornea  with  the 
sclerotic,  and  just  behind  the  outer  border  of  the  iris  (fig.  365). 
The  outermost  fibres  of  this  muscle  are  attached  in  front  to  the 
inner  part  of  the  sclerotic  and  cornea  at  their  line  of  junction,  and 


chap.  xix. |  ACCOMMODATION.  ~0^ 

diverging  somewhat,  are  fixed  fco  the  ciliary  pr<  .  and  a  Bmall 

portion  of  the  choroid  Immediately  behind  them.     The  inner  fibrea 
immediately  within  the  preceding,  form  a  circular  /one  around  the 
interior  of  the  eyeball,  outside  the  ciliary  processes.     Thej  com 
the  ring  formerly  called  the  ciliary  ligament. 

Accommodation  of  the  Eye. — The  distinctness  of  the  image 
formed  upon  the  retina,  is  mainly  dependent  on  the  rays  emitted 
by  each  luminous  point  <»f  the  object  being  brought  to  ;i  perfecl 
focus  upon  the  retina.  If  this  focus  occur  at  ;i  point  either  in 
front  of,  or  behind  the  retina,  indistinctness  of  vision  ensues,  with 
the  production  of  a  halo.  The  focal  distance,  i.e.,  the  distance  of 
the  point  at  winch  the  luminous  rays  from  a  lens  are  collected, 
besides  being  regulated  by  the  degree  of  convexity  and  density  of 
the  lens,  varies  with  the  distance  of  the  object  from  the  lens. 
being  greater  as  this  is  shorter,  and  vice  versa.  Hence,  since 
objects  placed  at  various  distances  from  the  eye  can,  within  a 
certain  range,  different  in  different  persons,  be  seen  with  almost 
equal  distinctness,  there  must  be  some  provision  by  which  the 
eye  is  enabled  to  adapt  itself,  so  that  whatever  length  the  focal 
distance  may  be,  the  focal  point  may  always  fall  exactly  upon  the 
retina. 

This  power  of  adaptation  of  the  eye  to  vision  at  different  distances 
has  received  the  most  varied  explanations.  It  is  obvious  that  the 
effect  might  be  produced  in  either  of  two  ways,  viz.,  by  altering 
the  convexity  or  intensity,  and  thus  the  refracting  power,  either  of 
the  cornea  or  lens  ;  or  by  changing  the  position  either  of  the  retina 
or  of  the  lens,  so  that  whether  the  object  viewed  be  near  or  distant. 
and  the  focal  distance  thus  increased  or  diminished,  the  focal  point 
to  which  the  rays  are  converged  by  the  lens  may  always  be  at  the 
place  occupied  by  .the  retina.  The  amount  of  either  of  these 
changes  required  in  even  the  widest  range  of  vision,  is  extremely 
small.  For,  from  the  refractive  powers  of  the  media  of  the  eye,  it 
has  been  calculated  by  Olbers,  that  the  difference  between  the 
focal  distances  of  the  images  of  an  object  at  such  a  distance  that 
the  rays  are  parallel,  and  of  one  at  the  distance  of  four  inches,  is 
only  about  0T43  of  an  inch.  On  this  calculation,  the  change  in 
the  distance  of  the  retina  from  the  lens  required  for  vision  at  all 
distances,  supposing  the  cornea  and  lens  to  maintain  the  same 
form,  would  not  be  more  than  about  one  line. 


704 


SEXSE   OF   SIGHT. 


[chap.  XIX. 


Fig.  .375. — Diagram  showing  three 
reflections  of  a  candle.  1,  From 
the  anterior  surface  of  cornea  : 
2,  from  the  anterior  surface  of 
lens  ;  3,  from  the  posterior  sur- 
face of  lens.  For  further  ex- 
planation, see  text.  The  experi- 
ment is  best  performed  by 
employing  an  instrument  in- 
vented by  Helmholtz,  termed  a 
Phakoscope . 


It  is  now  almost  universally  believed  that  Helmholtz  is  right  in 

his  statement  that  the  immediate  cause 
of  the  adaptation  of  the  eve  for  objects 
at  different  distances  is  a  varying  shape 
of  the  lens,  its  front  surface  becoming 
1  j  inre  or  less  convex,  according  to  the 
distance  of  the  object  looked  at.      The 
nearer   the    object,   the    more   convex 
does  the  front   surface  of  the  lens  be- 
come, and  vice  versa  ;  the  back  surface 
taking  little  or  no  share  in  the  produc- 
tion of  the  effect  required.     The  fol- 
lowing   simple    experiment    illustrates 
this  point.     If  a  small  flame  be  held 
little  to  one  side  of  a  person's  eye,  an 
observer  looking  at  the  eye 
from    the    other    side    sees 
three  distinct  images  of  the 
flame  (fig.  375).     The  first 
and  brightest  is  (1)  a  small 
erect     image     formed     by 
the  anterior  convex  surface 
of  the  cornea:    the  second 
( 2 )  is  also  erect,  but  larger 
and  less  distinct  than   the 
preceding,  and  is  formed  at 
the  anterior  convex  surface 
of  the  lens  :  the  third  (3)  is 
smaller  and  reversed,  it   is 
formed  at  the  posterior  sur- 
face  of  the  lens,   Avhich  is 
concave  forwards,  and  there- 
fore, like  all  concave  mirrors, 
gives  a  reversed  image.     If 
now  the  eye  under  observa- 
tion be  made  to  look  at  a 
near     object,     the     second 
image      becomes      smaller, 
clearer,  and  approaches  the 


Fig.  376. — Phakoscope  of  Helmholtz.  At  B  K  are 
two  prisms,  by  -which  the  light  of  a  candle  is 
concentrated  on  the  eye  of  the  person  experi- 
mented with  at  C ;  A  is  the  aperture  for  the  eye 
of  the  observer.  The  observer  notices  three  double 
images,  as  in  fig.  375,  reflected  from  the  eye 
under  examination  when  the  eye  is  fixed  upon 
a  distant  object ;  the  position  of  the  images  hav- 
ing been  noticed  the  eye  is  then  made  to  focus 
a  near  object,  such  as  a  needle  pushed  up  by  C; 
the  images  from  the  anterior  surface  of  the  lens 
will  be  observed  to  move  towards  each  other,  in 
consequence  of  the  lens  becoming  more  convex. 


chap.xix.]        MECHANISM    OF    ACCOMMODATION, 


705 


first.  If  the  eye  be  now  adjusted  for  a  far  point,  the  second  image 
enlarges  again,  becomes  Less  distinct,  :ui<l  recedes  from  the  first.     In 

both  eases  alike  the  first  and  third  images  remain  unaltered  in  size 
and  relative  position  This  proves  that  during  accommodation  for 
near  objects  the  curvature  of  the  crnea,  and  of  the  posterior  <»f  the 
lens,  remains  unaltered,  while  the  anterior  surface  of  the  lens 
becomes  more  convex  and  approaches  the  cornea. 

Mechanism  of  Accommodation. — Of  course  the  lens  has  no 
inherent  power  of  contraction,  and  therefore  its  changes  of  outline 
must  be  produced  by  some  power  from  without;  and  there  seems 
OO  reason  to  doubt  that  this  power  is  supplied  by  the  ciliary 
muscle.      It   is  sometimes  termed  the  tensor  ehoroidece.     As  this 


Fig.  377. — Diagram  representing  by  dotted  lines  the  alteration  in  the  shape  of  the  lens,  on  accom- 
modation for  near  objects.     (E.  Landolt.) 


name  implies,  from  its  attachment  (p.  702),  it  is  able  to  draw 
forwards  the  choroid,  and  therefore  slackens  the  tension  of  the  sus- 
pensory ligament  of  the  lens  which  arises  from  it.  The  lens  is 
usually  partly  flattened  by  the  action  of  the  suspensory  ligament  : 
and  the  ciliary  muscle  by  diminishing  the  tension  of  this  ligament 
diminishes,  to  a  proportional  degree,  the  flattening  of  which  it  is 
the  cause.  On  diminution  or  cessation  of  the  action  of  the  ciliary 
muscle,  the  lens  returns,  in  a  corresponding  degree,  to  its  former 
shape,  by  virtue  of  the  elasticity  of  its  suspensory  ligament  (fig.  377). 
From  this  it  will  appear  that  the  eye  is  usually  focussed  for  distant 
objects.  In  viewing  near  objects  the  pupil  contracts,  the  opposite 
effect  taking  place  on  withdrawal  of  the  attention  from  near 
objects,  and  fixing  it  on  those  distant. 

z  z 


yo6  SEXSE   OF   SIGHT.  [chap.  xix. 

Range  of  Distinct  Vision.  Near-point. — In  every  eye  there 
is  a  limit  to  the  power  of  accommodation.  If  a  book  be  brought 
nearer  and  nearer  to  the  eve,  the  type  at  last  becomes  indistinct 
and  cannot  be  brought  into  focus  by  any  effort  of  accommodation, 
however  strong.  This,  which  is  termed  the  near-point,  can  be 
determined  by  the  following  experiment  (Scheiner).  Two  small 
holes  are  pricked  in  a  card  with  a  pin  not  more  than  a  line 
apart,  at  any  rate  their  distance  from  each  other  must  not  exceed 
the  diameter  of  the  pupil.  The  card  is  held  close  in  front  of  the 
eye,  and  a  small  needle  viewed  through  the  pin-holes.  At  a 
moderate  distance  it  can  be  clearly  focussed,  but  when  brought 
nearer,  beyond  a  certain  point,  the  image  appears  double  or  at 


Kg.  378. — Diagram  of  experiment  to  ascertain  the  minimum  distance  of  distinct  vision. 

any  rate  blurred.  This  point  where  the  needle  ceases  to  appear 
single  is  the  near-point.  Its  distance  from  the  eye  can  of  course 
be  readily  measured.  It  is  usually  about  5  or  6  inches.  In  the 
accompanying  figure  (fig.  378)  the  lens  b  represents  the  eye  ;  ef 
the  two  pinholes  in  the  card,  nn  the  retina ;  a  represents  the 
position  of  the  needle.  When  the  needle  is  at  a  moderate  distance, 
the  two  pencils  of  light  coming  from  e  and  /,  are  focussed  at  a 
single  point  on  the  retina  nn.  If  the  needle  be  brought  nearer 
than  the  near-point,  the  strongest  effort  of  accommodation  is  not 
sufficient  to  focus  the  two  pencils,  they  meet  at  a  point  behind  the 
retina.  The  effect  is  the  same  as  if  the  retina  were  shifted  forward 
to  mm.  Two  images,  h,  g,  are  formed,  one  from  each  hole.  It  is 
interesting  to  note  that  when  two  images  are  produced,  the  lower 
one  g  really  appears  in  the  position  q,  while  the  upper  one  appears 
in  the  position  p.  This  may  be  readily  verified  by  covering  the 
holes  in  succession. 

The  contents  of  the  ball  of  the  eye  are  surrounded  and  kept  in 


I  HA1\    XIX.] 


COURSE    OF    A    RAT    OF    LIMIT. 


707 


bion  by  the  cornea^  and  the  dense,  fibrous  membrane  before 
referred  to  as  the  9clerotic.  which,  besides  thua  encasins  tlio 
contents  of   the  eye,   -      es  to   give  attachment  t..  the    various 

Lee   by  which  the  movements   of  the  eye-ball   arc 
Those  muscles,  and  the  nerves  supplying  them,  have  been  air 
sidered  (p.  '1::.  et  neq. ). 

Course  of  a  Ray  of  Light. — With  the  help  of  the  diagram 
(fig.  379)  representing  a  vertical  section  of  the  eye  from  before 
backwards,  the  mode  in  which,  by  means  of  the  refracting  media 
of  the  eve.  an  image  "fan  object  of  sight  is  thrown  on  the  retina, 
may  he  rendered  intelligible.  The  rays  of  the  cones  of  light 
emitted  by  the  points  a  b,  and  every  other  point  of  an  object 
placed  before  the  eye,  are  first  refracted,  that  is,  are  bent  towards 
the  axis  of  the  cue.  by  the  cornea  c  C,    and  the  aqueous  humour 


Fig.  379.— Course  of  a  ray  of  light. 


contained  between  it  and  the  lens.  The  rays  of  each  cone  are 
again  refracted  and  bent  still  more  towards  its  central  ray  or  axis 
by  the  anterior  surface  of  the  lens  e  e  :  and  again  as  they  pass  out 
through  its  posterior  surface  into  the  less  dense  medium  of  the 
vitreous  humour.  For  a  lens  has  the  power  of  refracting  and 
causing  the  convergence  of  the  rays  of  a  cone  of  light,  not  only  en 
their  entrance  from  a  rarer  medium  into  its  anterior  convex  surface, 
but  also  at  their  exit  from  its  posterior  convex  surface  into  the 
rarer  medium. 

In  this  manner  the  rays  of  the  cones  of  light  issuing  from  the 
points  a  and  b  are  again  collected  to  points  a  and  5  .•  and.  if  the 
retina  f  be  situated  at  a  and  &,  perfect,  though  reversed,  images  of 

z  z  -2 


;o3  SENSE   OF   SIGHT.  [chap,  xix 

the  points  a  and  b  will  be  formed  upon  it :  but  if  the  retina  be  not 
at  a  and  b,  but  either  before  or  behind  that  situation, — for  instance, 
at  h  or  g, — circular  luminous  spots  c  and  /,  or  e  and  o,  instead  of 
points,  will  be  seen ;  for  at  h  the  rays  have  not  yet  met,  and  at  g 
they  have  already  intersected  each  other,  and  are  again  diverging. 
The  retina  must  therefore  be  situated  at  the  proper  focal  distance 
from  the  lens,  otherwise  a  defined  image  will  not  be  formed ;  or, 
in  other  words,  the  rays  emitted  by  a  given  point  of  the  object 
will  not  be  collected  into  a  corresponding  point  of  focus  upon  the 
retina. 

Defects  in  the  Apparatus. 

A.  Defects  in  the  Refracting  Media. — Under  this  head  we 
may  consider  the  defects  known  as  (i)  Myopia,  (2)  Hypermetropia, 
(3)  Astigmatism,  (4)  Spherical  Aberration,  (5)  Chromatic  Aberra- 
tion. 

The  normal  (emmetropic)  eye  is  so  adjusted  that  parallel  rays 
are  brought  exactly  to  a  focus  on  the  retina  without  any  effort  of 
accommodation  (1,  fig.  380).  Hence  all  objects  except  near  ones 
(practically  all  objects  more  than  twenty  feet  off)  are  seen  without 
any  effort  of  accommodation ;  in  other  words,  the  far-point  of 
the  normal  eye  is  at  an  infinite  distance.  In  viewing  near  objects 
we  are  conscious  of  an  effort  (the  contraction  of  the  ciliary 
muscle)  by  which  the  anterior  surface  of  the  lens  is  rendered 
more  convex,  and  rays  which  would  otherwise  be  focussed  behind 
the  retina  are  converged  upon  the  retina  (see  dotted  lines,  2, 
fig.  380). 

1.  Myopia  (short-sight)  (4,  fig.  380). — This  defect  is  due  to  an 
abnormal  elongation  of  the  eye-ball.  The  eye  is  usually  larger 
than  normal,  and  is  always  longer  than  normal ;  the  lens  is  also 
probably  too  convex.  The  retina  is  too  far  from  the  lens,  and 
consequently  parallel  rays  are  focussed  in  front  of  the  retina,  and, 
crossing,  form  little  circles  on  the  retina ;  thus  the  images  of 
distant  objects  are  blurred  and  indistinct.  The  eye  is,  as  it  were, 
permanently  adjusted  for  a  near-point,  Rays  from  a  point  near 
the  eye  are  exactly  focussed  in  the  retina.  But  those  which  issue 
from  any  object  bej^ond  a  certain  distance  (far-point)  cannot  be 
distinctly  focussed.  This  defect  is  corrected  by  concave  glasses, 
which  cause  the  rays  entering  the   eye  to  diverge ;  hence  they  do 


ohap.  xix.]  DEFECTS  IN  THE  APPARATUS.  709 

not  come  to  a  focus  so  soon.  Such  glasses  of  course  are  only 
needed  to  give  a  clear  vision  of  distant  objects.  For  near  objects, 
except  iii  extreme  cases  they  are  not  required. 


Fig.  380. — Diagrams  showing — i,  normal  {emmetropic)  eye  bringing  parallel  rays  exactly  to  a 
focus  on  the  retina ;  2,  normal  eye  adapted  to  a  near  point ;  without  accommodation,  the 
rays  would  be  focussed  behind  the  retina,  but  by  increasing  the  curvature  of  the  an- 
terior surface  of  the  lens  (shown  by  a  dotted  line)  the  rays  are  focussed  on  the  retina 
(as  indicated  by  the  meeting  of  the  two  dotted  lines)  ;  3,  hypermetropic  eye,  in  this  case 
the  axis  of  the  eye  is  shorter,  and  the  lens  natter,  than  normal ;  parallel  rays  are 
focussed  behind  the  retina ;  4,  myopic  eye ;  in  this  case  the  axis  of  the  eye  is 
abnormally  long,  and  the  lens  too  convex ;  parallel  rays  are  focussed  in  front  of  the 
retina. 

2.  Hypermetropia  (long-sight)  (3,  fig.  380). — This  is  the 
reverse  defect.  The  eye  is  too  short  and  the  lens  too  flat. 
Parallel  rays  are  focussed  behind  the  retina  :  an  effort  of  accommo- 
dation is  required  to  focus  even  parallel  rays  on  the  retina  ;  and 
when  they  are  divergent,  as  in  viewing  a  near  object,  the  accommo- 


yiO  SEXSE   OF   SIGHT.  [chap.  xix. 

elation  is  insufficient  to  focus  them.  Thus  in  well-marked  cases 
distant  objects  require  an  effort  of  accommodation  and  near  ones  a 
very  powerful  eifort.  Thus  the  ciliary  muscle  is  constantly  acting. 
This  defect  is  obviated  by  the  use  of  convex  glasses,  which  render 
the  pencils  of  light  more  convergent.  Such  glasses  are  of  course 
especially  needed  for  near  objects,  as  in  reading,  etc.  They  rest 
the  eye  by  relieving  the  ciliary  muscle  from  excessive  work. 

3.  Astigmatism. — This  defect,  which  was  first  discovered  by 
Airy,  is  due  to  a  greater  curvature  of  the  eve  in  one  meridian 
than  in  others.  The  eye  may  be  even  myopic  in  one  plane  and 
hypermetropic  in  others.  Thus  vertical  and  horizontal  lines 
crossing  each  other  cannot  both  be  focussed  at  once  ;  one  set  stand 
out  clearly  and  the  others  are  blurred  and  indistinct.  This  defect, 
which  is  present  in  a  slight  degree  in  all  eyes,  is  generally  seated 
in  the  cornea,  but  occasionally  in  the  lens  as  well :  it  may  be  cor- 
rected by  the  use  of  cylindrical  glasses  {i.e.  curved  only  in  one 
direction). 

4.  Spherical  Aberration. — The  rays  of  a  cone  of  light  from 
an  object  situated  at  the  side  of  the  field  of  vision  do  not  meet 
all  in  the  same  point,  owing  to  their  unequal  refraction ;  for  the 
refraction  of  the  rays  which  pass  through  the  circumference  of  a 
lens  is  greater  than  that  of  those  traversing  its  central  portion. 
This  defect  is  known  as  spherical  aberration,  and  in  the  camera, 
telescope,  microscope,  and  other  optical  instruments,  it  is  remedied 
by  the  interposition  of  a  screen  with  a  circular  aperture  in  the 
path  of  the  rays  of  light,  cutting  off  all  the  marginal  rays  and 
only  allowing  the  passage  of  those  near  the  centre.  Such  correc- 
tion is  effected  in  the  eye  by  the  iris,  which  fonns  an  annular 
diaphragm  to  cover  the  circumference  of  the  lens,  and  to  prevent 
the  rays  from  passing  through  any  part  of  the  lens  but  its  centre 
which  corresponds  to  the  pupil.  The  posterior  surface  of  the  iris 
is  coated  with  pigment,  to  prevent  the  passage  of  rays  of  light 
through  its  substance.  The  image  of  an  object  will  be  most 
defined  and  distinct  when  the  pupil  is  narrow,  the  object  at  the 
proper  distance  for  vision,  and  the  light  abundant ;  so  that,  while 
a  sufficient  number  of  rays  are  admitted,  the  narrowness  of  the 
pupil  may  prevent  the  production  of  indistinctness  of  the  image 
by  spherical  aberration.  But  even  the  image  formed  by  the  rays 
passing  through  the  circumference  of  the  lens,  when  the  pupil  is 


:.  xix.]  CHKOMATIC    ABERRATION.  - 1  I 

much  diluted,  aa  in  the  dark,  or  in  a  C  _;tt,  may,  ondei 

tain  circumstances,  be  well  deft 

Distui  secured  by  the  outer  surffu 

the  retina  as  well  as  the  posterior  surface  of  the  iris  and  the  ciliary 

-  g  with  black  pigment,  which  absorbs  any  rayH 

«>f  light  that  may  be  reflected  within  the  eye,  and  prevents  their 

being  thrown  again   upon  the  retina  -      si        '   rfere  with  the 

res  1  I.     Thi        _    tent  of  the  retina  ially 

important  in   this   res       I  ;  for  with  the    exception  utt-r 

layer  the  retina   ifi  very  transparent,  and  if  the  surface  l)ehind 

it    were   not   of  a   dark   colour,    but    capabL  fleeting   the 

_    L  the  luminous  ravs  which  had   already  acted  on  the  retina 

■  ■ 

would  be  reflected  again  through   it,  and  would  fall  upon  other 
-  of  the  same  membrane,  producing  both  dazzling  from  e 
aid  indistinctness  of  the  im  _  s, 
5.   Chromatic  Aberration. — In  the   pass   _      :      _ht  through 
an  ordinary  convex  lens,  -  f  each  ray  into  it- 

mentaiy  coloured  pans  commonly      5     3,  and  a  • 
appears  around  the   im;i_  .       ing  1    the  unequal  refraction  which 
lementary  colours    and  rgo.      In  optical    instruments   this. 
which  is  termed  chrom  -  is  ted  by  the  us 

lenses,  differing  .  ipe  and  density,  the  - 

which  continues  or  inert  a  the  refraction  of  the  rays  produced 
l>y  the  first,  but  by  recombining  the  individual  parts  of  each  ray 
into  its  original  white  light,  corrects  any  chromatic  aberration 
which  may  have  resulted  from  the  first.  It  is  probable  that  the 
unequal  refractrv  r  of  the  transparent  media  in  front  of  the 

retina  may  be  the  means  by  which  the   e  ..aided  to  guard 

against  the  effect  of  chromatic  aberration.  The  human  eye  is 
achromatic,  however,  only  so  long  as  1  _  :  its 

focal  distance  upon  the  retina,  or  bo  long  as  the   eye  adapts  itself 
to  the  different  distances  of  sight.     If  either  of  these  condil 
be  interfered  with,  a  more  or  less  distinct  appearance  of  colon 
produced. 

An  ordinary  ray  of  white  light   in  passing  through  a  prisn 

refracted,  ent  out  of  its  course,  but  the  different  coloured 

which   goto  make  up  wh:-  -    are   refracted  in  different 

and  tie  appear     -  ored   bands  fading  off  into 

each  other:  thus  a  coloured  band  ki  th<    " spectrum "  is 


j  12  SENSE   OF   SIGHT.  [chap.  xix. 

produced  the  colours  of  which  are  arranged  as  follows, — red, 
orange,  yellow,  green,  blue,  indigo,  violet ;  of  these  the  red  ray  is 
the  least,  and  the  violet  the  most  refracted.  Hence,  as  Helm- 
holtz  has  shown,  a  small  white  object  cannot  be  accurately  focussed 
on  the  retina,  for  if  we  focus  for  the  red  rays,  the  violet  are  out  of 
focus,  and  vice  versa  :  such  objects,  if  not  exactly  focussed,  are 
often  seen  surrounded  by  a  pale  yellowish  or  bluish  fringe. 

For  similar  reasons  a  red  surface  looks  nearer  than  a  blue  one 
at  an  equal  distance,  because,  the  red  rays  being  less  refrangible,  a 
stronger  effort  of  accommodation  is  necessary  to  focus  them,  and 
the  eye  is  adjusted  as  if  for  a  nearer  object,  and  therefore  the  red 
surface  appears  nearer. 

From  the  insufficient  adjustment  of  the  image  of  a  small  white 
object,  it  appears  surrounded  by  a  sort  of  halo  or  fringe.  This 
phenomenon  is  termed  Irradiation.  It  is  from  this  reason  that  a 
white  square  on  a  black  ground  appears  larger  than  a  black  square 
of  the  same  size  on  white  ground. 

As  an  optical  instrument,  the  eye  is  superior  to  the  camera  in  the  following, 
among  many  other  particulars,  which  may  be  enumerated  in  detail,  i.  The 
correctness  of  images  even  in  a  large  field  of  view.  2.  The  simplicity  and 
efficiency  of  the  means  by  which  chromatic  aberration  is  avoided.  3.  The 
perfect  efficiency  of  its  adaptation  to  different  distances.  In  the  photo- 
graphic camera,  it  is  well  known  that  only  a  comparatively  small  object 
can  be  accurately  focussed.  In  the  photograph  of  a  large  object  near  at 
hand,  the  upper  and  lower  limits  are  always  more  or  less  hazy,  and  vertical 
lines  appear  curved.  This  is  due  to  the  fact  that  the  image  produced 
by  a  convex  lens  is  really  slightly  curved  and  can  only  be  received  without 
distortion  on  a  slightly  curved  concave  screen,  hence  the  distortion  on  a 
fat  surface  of  ground  glass.  It  is  different  with  the  eye,  since  it  possesses 
a  concave  background,  upon  which  the  field  of  vision  is  depicted,  and  with 
which  the  curved  form  of  the  image  coincides  exactly.  Thus,  the  defect 
of  the  camera  obseura  is  entirely  avoided  ;  for  the  eye  is  able  to  embrace 
a  large  field  of  vision,  the  margins  of  which  are  depicted  distinctly  and 
without  distortion.  If  the  retina  had  a  plane  surface  like  the  ground  glass 
plate  in  a  camera,  it  must  necessarily  be  much  larger  than  is  really  the  case 
if  we  were  to  see  as  much  ;  moreover,  the  central  portion  of  the  field  of 
vision  alone  would  give  a  good  clear  picture.     (Bernstein.) 

B.  Defective  Accommodation— Presbyopia. — This  condi- 
tion is  due  to  the  gradual  loss  of  the  power  of  accommodation 
which  is  part  of  the  general  decay  of  old  age.  In  consequence  the 
patient  would  be  obliged  in  reading  to  hold  his  book  further  and 
further  away  in  order  to  focus  the  letters,  till  at  last  the  letters 


chap.  xix.  |  Visr.\ I.    SENSATIONS.  715 

;uv  held  too  tar  for  distinct  vision.     The  defect   is  remedied  by 
weak  convex  glasses,  which  are  very  common] y  worn  by  old  people. 

It   is  due    chiefly    to    the  gradual    increase    in    density  of  the    lens, 
which  is  unable  to  swell  out  and  become  Convex    when  near  objects 

are  looked  at,  and  also  to  a  weakening  of  the  ciliary  muscle,  and  a 
general  hiss  of  elasticity  in  the  parts  concerned  in  the  mechanism. 


Visual  Sensations. 

Excitation  of  the  Retina. — Light  is  the  normal  agent  in  the 
excitation  of  the  retina,  the  only  layer  of  which  capable  of  re- 
acting  to  the  stimulus  being  the  rods  and  cones.  The  proofs  of 
this  statement  may  be  summed  up  thus  : — 

(1.)  The  point  of  entrance  of  the  optic  nerve  into  the  retina, 
where  the  rods  and  cones  are  absent,  is  insensitive  to  light  and  is 
called  the  blind  spot.  The  phenomenon  itself  is  very  readily  demon- 
strated. If  we  direct  one  eye,  the  other  being  closed,  upon  a  point  at 
such  a  distance  to  the  side  of  any  object,  that  the  image  of  the  latter 
must  fall  upon  the  retina  at  the  point  of  entrance  of  the  optic  nerve, 
this  image  is  lost  either  instantaneously,  or  very  soon.  If,  for 
example,  we  close  the  left  eye,  and  direct  the  axis  of  the  right  eye 


steadily  towards  the  circular  spot  here  represented,  while  the  page 
is  held  at  a  distance  of  about  six  inches  from  the  eye,  both  dot  and 
cross  are  visible.  On  gradually  increasing  the  distance  between 
the  eye  and  the  object,  by  removing  the  book  farther  and  farther 
from  the  face,  and  still  keeping  the  right  eye  steadily  on  the  dot, 
it  will  be  found  that  suddenly  the  cross  disappears  from  view. 
while  on  removing  the  book  still  farther,  it  suddenly  comes  in 
sight  again.  The  cause  of  this  phenomenon  is  simply  that  the 
portion  of  retina  which  is  occupied  by  the  entrance  of  the  optic 
nerve,  is  quite  blind  ;  and  therefore  that  when  it  alone  occupies 
the  field  of  vision,  objects  cease  to  lie  visible.  (2.)  In  the  fovea 
centralis  and  macula  lutea,  which  contain  rods  and  cones  but  no 
optic  nerve-fibres,  light  produces  the  greatest  effect.  In  the 
latter,  cones  occur  in  larger  numbers,  and  in  the  former  cones 
without  rods  are  found,  whereas  in  the  rest  of  the  retina  which  is 


714  SENSE   OF   SIGHT.  [chap.  xix. 

not  so  sensitive  to  light,  there  are  fewer  cones  than  rods.  We 
may  conclude,  therefore,  that  cones  are  even  more  important  to 
vision  than  rods.  (3.)  If  a  small  lighted  candle  be  moved  to  and 
fro  at  the  side  of  and  close  to  one  eve  in  a  dark  room  while  the 
eyes  look  steadily  forward  into  the  darkness,  a  remarkable  branch- 
ing figure  (Purkinje's  figures)  is  seen  floating  before  the  eye,  consist- 
ing of  dark  lines  on  a  reddish  ground.  As  the  candle  moves,  the 
figure  moves  in  the  opposite  direction,  and  from  its  whole  appear- 
ance there  can  be  no  doubt  that  it  is  a  reversed  picture  of  the 
retinal  vessels  projected  before  the  eye.  The  two  large  branching- 
arteries  passing  up  and  down  from  the  optic  disc  are  clearly  visible 
together  with  their  minutest  branches.  A  little  to  one  side  of  the 
disc,  in  a  part  free  from  vessels,  is  seen  the  yellow  spot  in  the 
form  of  a  slight  depression.  This  remarkable  appearance  is 
doubtless  due  to  shadows  of  the  retinal  vessels  cast  by  the  candle. 
The  branches  of  these  vessels  are  chiefly  distributed  in  the 
nerve-fibre  and  ganglionic  layers  ;  and  since  the  light  of  the  candle 
falls  on  the  retinal  vessels  from  in  front,  the  shadow  is  cast  behind 
them,  and  hence  those  elements  of  the  retina  which  perceive  the 
shadows  must  also  lie  behind  the  vessels.  Here,  then,  we  have  a 
clear  proof  that  the  light-perceiving  elements  of  the  retina  are  not 
the  fibres  of  the  optic  nerve  forming  the  innermost  layer  of  the 
retina,  but  the  external  layers  of  the  retina,  almost  certainly  the 
rods  and  cones,  which  indeed  appear  to  be  the  special  terminations 
of  the  optic  nerve-fibres. 

Duration  of  Visual  Sensations. — The  duration  of  the  sensa- 
tion produced  by  a  luminous  impression  on  the  retina  is  always 
greater  than  that  of  the  impression  which  produces  it.  However 
brief  the  luminous  impression,  the  effect  on  the  retina  always  lasts 
for  about  one-eighth  of  a  second.  Thus,  supposing  an  object  in 
motion,  say  a  horse,  to  be  revealed  011  a  dark  night  by  a  flash  of 
lightning.  The  object  would  be  seen  apparently  for  an  eighth  of 
a  second,  but  it  would  not  appear  in  motion ;  because,  although 
the  image  remained  011  the  retina  for  this  time,  it  was  really 
revealed  for  such  an  extremely  short  period  (a  flash  of  lightning 
being  almost  instantaneous)  that  no  appreciable  movement  on  the 
part  of  the  object  could  have  taken  place  in  the  period  during 
which  it  was  revealed  to  the  retina  of  the  observer.  And  the 
same  fact  is  proved  in  a  reverse  way.     The  spokes  of  a  rapidly 


chap.xix.]      DURATION    OF    VISUAL    SENSATIONS.  715 

revolving  wheel  are  ad  seen  as  distinct  objects,  because  ai  every 
point  of  the  field  of  vision  over  which  the  revolving  Bp 
given  impression  has  not  faded  before  another  comes  to  replace  it 
Thus  every  part  of  the  interior  of  the  wheel  appears  occupied. 

The  <lm-atii.ii  of  the  after-sensation,  produced  by  an  object,  is 

ater  in  a  direct  ratio  with  the  duration  of  the  impression  which 
caused  it.  Hence  the  image  of  a  bright  object,  as  of  the  panes  of 
a  window  through  which  the  light  is  Bhining,  may  be  perceived  in 
the  retina  for  a  considerable  period,  if  we  have  previously  kept  our 
eves  fixed  for  some  time  on  it.  But  the  image  in  this  case  is 
negative.  If,  however,  after  shutting  the  eyes  for  some  time,  we 
open  them  and  look  at  an  object  for  an  instant,  and  again  cl< 
them,  the  after-image  is  positive. 

Intensity  of  Visual  Sensations. — It  is  quite  evident  that  the 
more  luminous  a  body  the  more  intense  is  the  sensation  it  pro- 
duces. But  the  intensity  of  the  sensation  is  not  directly  propor- 
tional to  the  intensity  of  the  luminosity  of  the  object.  It  is  neces- 
sary for  light  to  have  a  certain  intensity  before  it  can  excite  the 
retina,  but  it  is  impossible  to  fix  an  arbitrary  limit  to  the  power  of 
excitability.  As  in  other  sensations,  so  also  in  visual  sensations, 
a  stimulus  may  be  too  feeble  to  produce  a  sensation.  If  it  be 
increased  in  amount  sufficiently  it  begins  to  produce  an  effect 
which  is  increased  on  the  increase  of  the  stimulation;  this  increase 
in  the  effect  is  not  directly  proportional  to  the  increase  in  the 
excitation,  but,  according  to  Fechner's  law,  "'as  the  logarithm  of 
the  stimulus/'  i.e.,  in  each  sensation,  there  is  a  constant  ratio 
between  the  increase  in  the  stimulus  and  the  increase  in  the 
sensation,  this  constant  ratio  for  each  sensation  expresses  the  least 
perceptible  increase  in  the  sensation  or  minimal  increment  of 
excitation. 

This  law,  which  is  true  only  within  certain  limits,  may  be  best 
understood  by  an  example.  When  the  retina  has  been  stimulated 
by  the  light  of  one  candle,  the  light  of  two  candles  will  produce  a 
difference  in  sensation  which  can  be  distinctly  felt.  If,  however, 
the  first  stimulus  had  been  that  of  an  electric  light,  the  addition 
of  the  light  of  a  candle  would  make  no  difference  in  the  sensation. 
So,  generally,  for  an  additional  stimulus  to  be  felt,  it  may  be 
proportionately  small  if  the  original  stimulus  have  been  small,  and 
must  be  greater  if  the  original  stimulus  have  been  great.     The 


y\6  SENSE   OF   SIGHT.  [chap.  xix. 

stimulus  increases  as  the  ordinary  numbers,  while  the  sensation 
increases  as  the  logarithm. 

The  Ophthalmoscope. — Part  of  the  light  which  enters  the  eye 
is  absorbed,  and  produces  some  change  in  the  retina,  of  which  we 
shall  treat  further  on ;  the  rest  is  reflected. 

Every  one  is  perfectly  familiar  with  the  fact,  that  it  is  quite 
impossible  to  see  the  fundus  or  back  of  another  person's  eye  by 
simply  looking  into  it.  The  interior  of  the  eye  forms  a  perfectly 
black  background  to  the  pupil.  The  same  remark  applies  to  an 
ordinary  photographic  camera,  and  may  be  illustrated  by  the 
difficulty  we  experience  in  seeing  into  a  room  from  the  street 
through  the  window,  unless  the  room  be  lighted  within.  In  the 
case  of  the  eye  this  fact  is  partly  due  to  the  feebleness  of  the  light 
reflected  from  the  retina,  most  of  it  being  absorbed  by  the  choroid, 
as  mentioned  above ;  but  far  more  to  the  fact  that  every  such  ray 
is  reflected  straight  back  to  the  source  of  light  (e.g.,  candle),  and 
cannot,  therefore,  be  seen  by  the  unaided  eye  without  intercepting 
the  incident  light  from  the  candle,  as  well  as  the  reflected  rays 
from  the  retina.  This  difficulty  has  been  surmounted  by  the 
ingenious  device  of  Helmholtz,  now  so  extensively  used,  termed 
the  ophtha/moscope.  As  at  present  used,  it  consists  of  a  small  slightly 
concave  mirror,  by  which  light  is  reflected  from  a  candle  into  the 
eye.  The  observer  looks  through  a  hole  in  the  mirror,  and  can 
thus  explore  the  illuminated  fundus  ;  the  entrance  of  the  optic 
nerve  and  the  retinal  vessels  being  plainly  visible. 

Visual  Purple. — The  method  by  which  a  ray  of  light  is  able 
to  stimulate  the  endings  of  the  optic  nerve  in  the  retina  in  such  a 
manner  that  a  visual  sensation  is  perceived  by  the  cerebrum 
is  not  yet  understood.  It  is  supposed  that  the  change  effected 
by  the  agency  of  the  light  which  falls  upon  the  retina  is  in  fact 
a  chemical  alteration  in  the  protoplasm,  and  that  this  change 
stimulates  the  optic  nerve-endings.  The  discovery  of  a  certain 
temporary  reddish-purple  pigmentation  of  the  outer  limbs  of  the 
retinal  rods  in  certain  animals  (e.g.  frogs)  which  have  been  killed 
in  the  dark,  forming  the  so-called  visual  purple,  appeared  likely  to 
offer  some  explanation  of  the  matter,  especially  as  it  was  also  found 
that  the  pigmentation  disappeared  when  the  animal  was  exposed 
to  light,  and  re-appeared  when  the  light  was  removed,  and  also 
that  it  underwent  distinct  changes  of  colour  when  other  than  white 


i   IIAI'.    XIX.  ] 


VISUAL  PEECEPTIONS. 


717 


light  was  used.  The  visual  purple  cannot  however  be  absolutely 
essentia]  to  the  due  production  of  visual  sensations,  as  it  is  absent 

from  the  retinal  cones,  and  from  the  macula  lntea  and  fovea 
centralis  of  the  human  retina,  and  does  not  appear  to  exist  at  all 
in  the  retinas  of  some  animals,  e.g.,  bat,  dove,  and  hen,  which  are, 
nevertheless,  possessed  of  good  vision. 

If  the  operation  be  performed  quickly  enough,  the  image  of  an  object  may 
be  fixed  in  the  pigment  on  the  retina  by  soaking  the  retina  of  an  animal, 
which  has  been  killed  in  (he  dark,  in  alum  solution. 

Electrical  Currents. — According  to  the  careful  researches  of 
Dewar  and  McKendrick,  and  of  Holmgren,   it  appears  that  the 

stimulus  of  light  is  able  to  produce  a  variation  of  the  natural 
electrical  current  of  the  retina.  The  current  is  at  first  increased 
and  then  diminished.  McKendrick  believes  that  this  is  the 
electrical  expression  of  those  chemical  changes  in  the  retina  of 
which  we  have  already  spoken. 


Visual  Perceptions  and  Judgments. 

Reversion  of  the  Image. — The  direction  given  to  the  rays 
by  their  refraction  is  regulated  by  that  of  the  central  ray,  or  axis 
of  the  cone,  towards  which  the  rays  are  bent.  The  image  of  any 
point  of  an  object  is,  therefore,  as  a  rule  (the  exceptions  to  which 


Fig.  381. — Diagram  of  the  formation  of  the  image  on  the  retina. 

need  not  here  be  stated),  always  formed  in  a  line  identical  with 
the  axis  of  the  cone  of  light,  as  in  the  line  of  b  a,  or  a  b  (fig.  381), 
so  that  the  spot  where  the  image  of  any  point  will  be  formed  upon 
the  retina  may  be  determined  by  prolonging  the  central  ray  of  the 
cone  of  light,  or  that  ray  which  traverses  the  centre  of  the 
pupil.  Thus  a  b  is  the  axis  or  central  ray  of  the  cone  of  light 
issuing  from  a  ;  b  a  the  central  ray  of  the  cone  of  light  issuing 
from  b  ;  the  image  of  a  is  formed  at  b,  the  image  of  b  at  a,  in  the 


yiS  SENSE    OF    SIGHT.  [chap.  xix. 

inverted  position ;  therefore  what  in  the  object  was  above  is  in  the 
image  below,  and  vice  versa, — the  right  hand  part  of  the  object  is  in 
the  image  to  the  left,  the  left-hand  to  the  right.  If  an  opening  be 
made  in  an  eye  at  its  superior  surface,  so  that  the  retina  can  be 
seen  through  the  vitreous  humour,  this  reversed  image  of  any 
bright  object,  such  as  the  windows  of  the  room,  may  be  perceived 
at  the  bottom  of  the  eye.  Or  still  better,  if  the  eye  of  any  albino 
animal,  such  as  a  white  rabbit,  in  which  the  coats,  from  the 
absence  of  pigment,  are  transparent,  is  dissected  clean,  and  held 
with  the  cornea  towards  the  window,  a  very  distinct  image  of  the 
window  completely  inverted  is  seen  depicted  on  the  posterior 
translucent  wall  of  the  eye.  Yolkmann  has  also  shown  that  a 
similar  experiment  may  be  successfully  performed  in  a  living  person 
possessed  of  large  prominent  eyes,  and  an  unusually  transparent 
sclerotic. 

An  image  formed  at  any  point  on  the  retina  is  referred  to  a 
point  outside  the  eye,  lying  on  a  straight  line  drawn  from  the  point 
on  the  retina  outwards  through  the  centre  of  the  pupil.  Thus  an 
image  on  the  left  side  of  the  retina  is  referred  by  the  mind  to  an 
object  on  the  right  side  of  the  eye,  and  vice  versa.  Thus  all 
images  on  the  retina  are  mentally,  as  it  were,  projected  in  front  of 
the  eye,  and  the  objects  are  seen  erect  though  the  image  on  the 
retina  is  reversed.  Much  needless  confusion  and  difficulty  have 
been  raised  on  this  subject  for  want  of  remembering  that  when  we 
are  said  to  see  an  object,  the  mind  is  merely  conscious  of  the 
picture  on  the  retina,  and  when  it  refers  it  to  the  external  object, 
or  "projects"  it  outside  the  e}'e,  it  necessarily  reverses  it  and  sees 
the  object  as  erect,  though  the  retinal  image  is  inverted.  This  is 
further  corroborated  by  the  sense  of  touch.  Thus  an  object 
whose  picture  falls  on  the  left  half  of  the  retina  is  reached  by  the 
right  hand,  and  hence  is  said  to  lie  to  the  right.  Or,  again,  an 
object  whose  image  is  formed  on  the  upper  part  of  the  retina  is 
readily  touched  by  the  feet,  and  is  therefore  said  to  be  in  the 
lower  part  of  the  field,  and  so  on. 

Hence  it  is,  also,  that  no  discordance  arises  between  the  sensa- 
tions of  inverted  vision  and  those  of  touch,  which  perceives  every- 
thing in  its  erect  position  ;  for  the  images  of  all  objects,  even  of 
our  own  limbs,  in  the  retina,  are  equally  inverted,  and  therefore 
maintain  the  same  relative  position. 


thai',  wx.]  VISUAL    PERCEPTIONS.  719 

Even  the  image  of  our  band,  while  used  in  touch,  is  seen  in- 
verted. The  position  in  which  we  Bee  objects,  we  call,  therefore, 
the  erect  position.  A  mere  lateral  inversion  of  our  body  in  a 
mirror,  where  the  right  hand  occupies  the  left  of  the  image,  is 
indeed  Bcarcely  remarked:  and  there  is  but  little  discordance 
between  the  sensations  acquired  by  touch  in  regulating  our  move- 
ment- by  the  image  in  the  mirror,  and  those  of  sight,  as,  for 
example,  in  tying  a  knot  in  the  cravat.  There  is  some  want  of 
harmony  here,  on  account  of  the  inversion  being  only  lateral,  and 
not  complete  in  all  directions. 

The  perception  of  the  erect  position  of  objects  appears,  there- 
fore, to  be  the  result  of  an  act  of  the  mind.  And  this  leads  US  to 
a  consideration  of  the  several  other  properties  of  the  retina,  and  of 
the  co-operation  of  the  mind  in  the  several  other  parts  of  the  act 
of  vision.  To  these  belong  not  merely  the  act  of  sensation  itself 
and  the  perception  of  the  changes  produced  in  the  retina,  as  light 
and  colours,  but  also  the  conversion  of  the  mere  images  depicted 
in  the  retina  into  ideas  of  an  extended  field  of  vision,  of  proximity 
and  distance,  of  the  form  and  size  of  objects,  of  the  reciprocal 
influence  of  different  parts  of  the  retina  upon  each  other,  the 
simultaneous  action  of  the  two  eyes,  and  some  other  phenomena. 

Field  of  Vision. — The  actual  size  of  the  field  of  vision  depends 
on  the  extent  of  the  retina,  for  only  so  many  images  can  be  seen  at 
any  one  time  as  can  occupy  the  retina  at  the  same  time  ;  and  thus 
considered,  the  retina,  of  which  the  affections  are  perceived  by  the 
mind,  is  itself  the  field  of  vision.  But  to  the  'mind  of  the  individual 
the  size  of  the  field  of  vision  has  no  determinate  limits  ;  sometimes 
it  appears  very  small,  at  another  time  very  large  ;  for  the  mind 
has  the  power  of  projecting  images  on  the  retina  towards  the 
exterior.  Hence  the  mental  field  of  visi<  »n  is  very  small  when  the 
sphere  of  the  action  of  the  mind  is  limited  to  impediments  near 
the  eye  :  on  the  contrary,  it  is  very  extensive  when  the  projection 
of  the  images  on  the  retina  towards  the  exterior,  by  the  influence 
of  the  mind,  is  not  impeded.  It  is  very  small  when  we  look  into 
a  hollow  body  of  small  capacity  held  before  the  eyes  ;  large  when 
we  look  out  upon  the  landscape  through  a  small  opening \  more 
extensive  when  we  look  at  the  landscape  through  a  window;  and 
most  so  when  our  view  is  not  confined  by  any  near  object.  In  all 
these  cases  the  idea  which  we  receive  of  the  size  of  the  field  of 


720 


SENSE   OF   SIGHT. 


[chap.  XIX. 


vision  is  very  different,  although  its  absolute  size  is  in  all  the 
same,  being  dependent  on  the  extent  of  the  retina.  Hence  it 
follows,  that  the  mind  is  constantly  co-operating  in  the  acts  of 
vision,  so  that  at  last  it  becomes  difficult  to  say  what  belongs  to 
mere  sensation,  and  what  to  the  influence  of  the  mind.  By  a 
mental  operation  of  this  kind,  we  obtain  a  correct  idea  of  the  size 
of  individual  objects,  as  well  as  of  the  extent  of  the  field  of  vision. 
To  illustrate  this,  it  will  be  well  to  refer  to  fig.  382. 

The  angle  x,  included  between  the  decussating  central  rays  of 
two  cones  of  light  issuing  from  different  points  of  an  object,  is 
called  the  optical  angle — angulus  opticus  sen   visorius.     This  angle 


Fig.  j?2. — Diagram  of  the  optical  angle, 

becomes  larger,  the  greater  the  distance  between  the  points  a  and 
b  ;  and  since  the  angles  x  and  y  are  equal,  the  distance  between 
the  points  a  and  h  in  the  image  on  the  retina  increases  as  the 
angle  becomes  larger.  Objects  at  different  distances  from  the  eye, 
but  having  the  same  optical  angle  x — for  example,  the  objects,  c,  d, 
and  e, — must  also  throw  images  of  equal  size  upon  the  retina  ;  and, 
if  they  occupy  the  same  angle  of  the  field  of  vision,  their  image  must 
occupy  the  same  spot  in  the  retina. 

Nevertheless,  these  images  appear  to  the  mind  to  be  of  very 
unequal  size  when  the  ideas  of  distance  and  proximity  come  into 
play  :  fur,  from  the  image  a  b,  the  mind  forms  the  conception  of  a 
visual  space  extending  to  e,  d,  or  c,  and  of  an  object  of  the  size 
which  that  represented  by  the  image  on  the  retina  appears  to  have 
when  viewed  close  to  the  eye,  or  under  the  most  usual  circum- 
stances. 

Estimation  of  Size. — Our  estimate  of  the  size  of  various 
objects  is  based  partly  on  the  visual  angle  under  which  they  are 
seen,  but  much  more  on  the  estimate  we  form  of  their  distance. 
Thus  a  lofty  mountain  many  miles  off  may  be  seen  under  the  same 
visual  angle  as  a  small  hill  near  at  hand,  but  we  infer  that  the 


ciiAi-.  xix.]  ESTIMATION    OF    FOBM.  721 

former  is  much  the  Larger  object  because  we  know  a  is  much 
further  off  than  the  hill.  Our  estimate  of  distance  is  often 
erroneous,  and  consequently  the  estimate  of  size  also.  Thus 
persons  seen  walking  on  the  top  of  a  small  hill  against  a  clear 
twilight  skv  appear  unusually  large,  because  we  over-estimate 
their  distance,  and  for  similar  reasons  most  objects  in  a  fog  appear 
immensely  magnified.  The  same  mental  process  gives  rise  to  the 
idea  of  depth  in  the  held  of  vision;  this  idea  being  fixed  incur 
mind  principally  by  the  circumstance  that,  as  we  ourselves  move 
forwards,  different  images  in  succession  become  depicted  on  our 
retina,  so  that  we  seem  to  pass  between  these  images,  which  to  the 
mind  is  the  same  thing  as  passing  between  the  objects  themselves. 

The  action  of  the  sense  of  vision  in  relation  to  external  objects 
is,  therefore,  quite  different  from  that  of  the  sense  of  touch.  The 
objects  of  the  latter  sense  are  immediately  present  to  it ;  and  our 
own  body,  with  which  they  come  into  contact,  is  the  measure  of 
their  size.  The  part  of  a  table  touched  by  the  hand  appears  as 
large  as  the  part  of  the  hand  receiving  an  impression  from  it,  for 
a  part  of  our  body  in  which  a  sensation  is  excited,  is  here  the 
measure  by  which  we  judge  of  the  magnitude  of  the  object.  In 
the  sense  of  vision,  on  the  contrary,  the  images  of  objects  are  mere 
fractions  of  the  objects  themselves  realised  upon  the  retina,  the 
extent  of  which  remains  constantly  the  same.  But  the  imagina- 
tion, which  analyses  the  sensations  of  vision,  invests  the  images  of 
objects,  together  with  the  whole  field  of  vision  in  the  retina,  with 
very  varying  dimensions ;  the  relative  size  of  the  image  in 
proportion  to  the  whole  field  of  vision,  or  of  the  affected  parts  of 
the  retina  to  the  whole  retina,  alone  remaining  unaltered. 

Estimation  of  Direction. — The  direction  in  which  an  object  is 
seen,  depends  on  the  part  of  the  retina  which  receives  the  image,  and 
on  the  distance  of  this  part  from,  and  its  relation  to,  the  central 
point  of  the  retina.  Thus,  objects  of  which  the  images  fall  upon 
the  same  parts  of  the  retina  lie  in  the  same  visual  direction  ;  and 
when,  by  the  action  of  the  mind,  the  images  or  affections  of  the 
retina  are  projected  into  the  exterior  world,  the  relation  of  the  images 
to  each  other  remains  the  same. 

Estimation  of  Form. — The  estimation  of  the  form  of  bodies 
by  sight  is  the  result  partly  of  the  mere  sensation,  and  partly  of 
the  association  of  ideas.     Since  the  form  of  the  images  perceived 

3  A 


722  SENSE   OF   SIGHT.  [chap.  xix. 

by  the  retina  depends  wholly  on  the  outline  of  the  part  of  the 
retina  affected,  the  sensation  alone  is  adequate  to  the  distinction  of 
only  superficial  forms  of  each  other,  as  of  a  square  from  a  circle. 
But  the  idea  of  a  solid  body  as  a  sphere,  or  a  body  of  three  or  more 
dimensions,  e.g.,  a  cube,  can  only  be  attained  by  the  action  of  the 
mind  constructing  it  from  the  different  superficial  images  seen  in 
different  positions  of  the  eye  with  regard  to  the  object,  and,  as 
shown  by  Wheatstone  and  illustrated  in  the  stereoscope ,  from  two 
different  perspective  projections  of  the  body  being  presented 
simultaneously  to  the  mind  by  the  two  eyes.  Hence,  when,  in 
adult  age,  sight  is  suddenly  restored  to  persons  blind  from  infancy, 
all  objects  in  the  field  of  vision  appear  at  first  as  if  painted  fiat  on 
one  surface  :  and  no  idea  of  solidity  is  formed  until  after  long 
exercise  of  the  sense  of  vision  combined  with  that  of  touch. 

The  clearness  with  which  an  object  is  perceived  irrespective  of 
accommodation,  would  appear  to  depend  largely  on  the  number 
of  rods  and  cones  which  its  retinal  image  covers.  Hence  the 
nearer  an  object  is  to  the  eye  (within  moderate  limits)  the  more 
clearly  are  all  its  details  seen.  Moreover,  if  we  want  carefully  to 
examine  any  object,  we  always  direct  the  eyes  straight  to  it,  so 
that  its  image  shall  fall  on  the  yellow  spot  where  an  image  of  a 
given  area  will  cover  a  larger  number  of  cones  than  anywhere  else 
in  the  retina.  It  has  been  found  that  the  images  of  two  points 
must  be  at  least  12o00  in.  apart  on  the  yellow  spot  in  order  to  be 
distinguished  separately  :  if  the  images  are  nearer  together,  the 
points  appear  as  one.  The  diameter  of  each  cone  in  this  part  of 
the  retina  is  about  1 2 1 0  0  in. 

Estimation  of  Movement. — "We  judge  of  the  motion  of  an 
object,  partly  from  the  motion  of  its  image  over  the  surface  of  the 
retina,  and  partly  from  the  motion  of  our  eyes  following  it.  If 
the  image  upon  the  retina  moves  while  our  eyes  and  our  body  are 
at  rest,  we  conclude  that  the  object  is  changing  its  relative  position 
with  regard  to  ourselves.  In  such  a  case  the  movement  of  the 
object  may  be  apparent  only,  as  when  we  are  standing  upon  a  body 
which  is  in  motion,  such  as  a  ship.  If,  on  the  other  hand,  the 
image  does  not  move  with  regard  to  the  retina,  but  remains  fixed 
upon  the  same  spot  of  that  membrane,  while  our  eyes  follow  the 
moving  body,  we  judge  of  the  motion  of  the  object  by  the  sensa- 
tion of  the  muscles  in  action  to  move  the  eye.     If  the  image  moves 


CHAP,  xix.]  COLOUR  SENSATIONS.  723 

over  the  surface  of  the  retina  while  the  muscles  of  the  eye  arc 
acting  at  the  same  time  in  ;i  manner  corresponding  to  this  motion, 

as  in  reading,  we  infer  that  the  object  is  stationary,  and  we  know 
that  we  are  merely  altering  the  relations  of  our  eyes  to  the  object. 
Sometimes  the  object  appears  to  move  when  both  object  and  eye 
are  fixed,  as  in  vertigo. 

The  mind  can,  by  the  faculty  of  attention,  concentrate  its  activity 
more  or  less  exclusively  upon  the  sense  of  sight,  hearing,  and 
touch  alternately.     "When  exclusively  occupied  with  the  action  of 
one  sense,  it  is  scarcely  conscious  of  the  sensations  of  the  others. 
The   mind,  when  deeply  immersed  in  contemplations  of  another 
nature,  is  indifferent  to  the  actions  of  the  sense  of  sight,  as  of  every 
other  sense.     We  often,  when  deep  in  thought,  have  our  eyes  open 
and  fixed,  but  see  nothing,  because  of  the  stimulus  of  ordinary 
light  being  unable  to  excite  the  brain  to  perception,  when  other- 
wise engaged.     The  attention  which  is  thus  necessary  for  vision,  is 
necessary  also  to   analyse  what  the  field  of  vision  presents.     The 
mind  does  not  perceive  all  the  objects  presented  by  the  field  of 
vision  at  the   same  time  with  equal  acuteness,  but  directs  itself 
first  to  one  and  then  to  another.     The  sensation  becomes  more 
intense,  according  as  the  particular  object  is  at  the  time  the  prin- 
cipal object  of  mental   contemplation.      Any  compound   mathe- 
matical   figure  produces  a  different  impression    ac- 
cording as  the  attention  is  directed   exclusively  to 
one   or  the  other  part  of  it.     Thus  in  fig.  383,  we 
may  in  succession  have  a  vivid  perception  of  the 
whole,  or  of  distinct  parts  only ;  of  the  six  triangles 
near  the  outer  circle,  of  the  hexagon  in  the  middle,  Fig.  383. 

or  of  the  three  large  triangles.  The  more  nume- 
rous and  varied  the  parts  of  which  a  figure  is  composed,  the  more 
scope  does  it  afford  for  the  play  of  the  attention.  Hence  it  is 
that  architectural  ornaments  have  an  enlivening  effect  on  the 
sense  of  vision,  since  they  afford  constantly  fresh  subject  for  the 
action  of  the  mind. 

Colour  Sensations. — If  a  ray  of  sunlight  be  allowed  to  pass 
through  a  prism,  it  is  decomposed  by  its  passage  into  rays  of  dif- 
ferent colours,  which  are  called  the  colours  of  the  spectrum  ;  they 
are  red,  orange,  yellow,  green,  blue,  indigo,  and  violet.    The  red  rays 

3  a  2 


724 


SENSE   OF   SIGHT.  [chap.  xix. 


are  the  least  turned  out  of  their  course   by  the  prism,  and  the 
violet  the  most,  whilst  the  other  colours  occupy  in  order  places 
between  these  two  extremes.     The  differences  in  the  colour  of  the 
rays,  depend  upon  the  number  of  vibrations  producing  each,  the 
red  rays  being  the  least  rapid  and  the  violet  the  most.     In  addition 
to  the  coloured  rays  of  the  spectrum,  there  are  others  which  are 
invisible,  but  which  have  definite  properties,  those  to  the  left  of 
the  red,  and  less  refrangible,  being  the   calorific   rays  which  act 
upon  the  thermometer,  and  those  to  the  right  of  the  violet  which 
are   called   the  actinic  or  chemical  rays,  which  have   a  powerful 
chemical  action.     The  rays  which  can  be  perceived  by  the  brain  as 
visual  rays,  i.e.,  the  coloured  rays,  must   stimulate   the  retina  in 
some  special   manner  in   order  that   coloured   vision   may  result, 
and   two   chief  explanations   of  the  method  of  stimulation   have 
been  suggested.      The  one,  originated  by  Young  and  elaborated  by 
Helmholtz,  holds  that  there  are  three  primary  colours,  viz.,  red, 
o-reen,  and  violet,   and  that   in  the  retina  are  contained  rods  or 
cones  which  answer  to  each  of  these  primary  colours,  whereas  the 
innumerable  intermediate  shades  of  colour  are  produced  by  stimu- 
lation of  the   three  primary  colour  terminals  in  different  degrees  ; 
the  sensation  of  white  being  produced  when  the  three  elements  are 
equally  excited.      Thus  if  the    retina  be  stimulated  by   rays   of 
certain  wave  length,  at  the  red  end  of  the  spectrum,  the  terminals 
of  the  other  colours  green  and  violet,  are  hardly  stimulated  at  all, 
but  the  red  terminals  being  strongly  stimulated,  the  resulting  sensa- 
tion is  red.      The   orange  rays  excite  the  red  terminals  consider- 
ably, the  green  rather  more,  and  the  violet   slightly,  the  resulting 
sensation  being  that  of  orange,  and  so  on. 

The  second  theory  of  colour  (Hering's)  supposes  that  there  are 
six  primary  colour  sensations,  of  three  pair  of  antagonistic  or  com- 
plemental  colours,  black  and  white,  red  and  green,  and  yellow  and 
blue,  and  that  these  are  produced  by  the  changes  either  of  disinte- 
gration or  of  assimilation  taking  place  in  certain  substances,  some- 
what it  may  be  supposed  of  the  nature  of  the  visual  purple,  which 
(the  theory  supposes  to)  exist  in  the  retina.  Each  of  the  sub- 
stances corresponding  to  a  pair  of  colours,  being  capable  of  under- 
going two  changes,  one  of  construction  and  the  other  of  disinte- 
gration, with  the  result  of  producing  one  or  other  colour.  For 
instance,   in  the   white-black  substance,  when  disintegration  is  in 


CHAP,  xix.]  COLOUR   SENSATION?.  725 

excess  of  construction  or  assimilation,  the  sensation  is  white,  and 
when  assimilation  is  in  excess  of  disintegration  tin;  reverse  is  the 
case  ;  and  similarly  with  the  red-green  substance,  and  with  the 
yellow-blue  substance.     When  the  repair  and  disintegration  are 

equal  with  the  first  substance,  the  visual  sensation  is  grey;  but 
in  the  other  pairs  when  this  is  the  case,  no  sensation  occurs.  The 
rays  of  the  spectrum  to  the  left  produce  changes  in  the  red-green 
substance  only,  with  a  resulting  sensation  of  red,  whilst  the 
(orange)  rays  further  to  the  right  affect  both  the  red-green  and 
the  yellow-blue  substances  ;  blue  rays  cause  constructive  changes 
in  the  yellow-blue  substance,  but  none  in  the  red-green,  and  so 
on.  These  changes  produced  in  the  visual  substances  in  the 
retina  are  perceived  by  the  brain  as  sensations  of  colour. 

The  spectra  left  by  the  images  of  white  or  luminous  objects,  are 
ordinarily  white  or  luminous ;  those  left  by  dark  objects  are  dark. 
Sometimes,  however,  the  relation  of  the  light  and  dark  parts  in 
the  image  may,  under  certain  circumstances,  be  reversed  in  the 
spectrum;  what  was  bright  may  be  dark,  and  what  was  dark 
may  appear  light.  This  occurs  whenever  the  eye,  which  is  the 
seat  of  the  spectrum  of  a  luminous  object,  is  not  closed,  but  fixed 
upon  another  bright  or  white  surface,  as  a  white  wall,  or  a  sheet 
of  white  paper.  Hence  the  spectrum  of  the  sun,  which,  while 
light  is  excluded  from  the  eye  is  luminous,  appears  black  or  grey 
when  the  eye  is  directed  upon  a  white  surface.  The  explanation  of 
this  is,  that  the  part  of  the  retina  which  has  received  the  luminous 
image  remains  for  a  certain  period  afterwards  in  an  exhausted 
or  less  sensitive  state,  while  that  which  has  received  a  dark  image 
is  in  an  unexhausted,  and  therefore  much  more  excitable  condition. 

The  ocular  spectra  which  remain  after  the  impression  of  coloured 
objects  upon  the  retina  are  always  coloured  ;  and  their  colour  is 
not  that  of  the  object,  or  of  the  image  produced  directly  by  the 
object,  but  the  opposite,  or  complemented  colour.  The  spectrum  of 
a  red  object  is,  therefore,  green ;  that  of  a  green  object,  red ;  that 
of  violet,  yellow ;  that  of  yellow,  violet,  and  so  on.  The  reason 
of  this  is  obvious.  The  part  of  the  retina  which  receives,  say,  a 
red  image,  is  wearied  by  that  particular  colour,  but  remains  sensi- 
tive to  the  other  rays  which  with  red  make  up  white  light ;  and, 
therefore,  these  by  themselves  reflected  from  a  white  object  produce 
a  green  hue.     If,  on  the  other  hand,  the  first  object  looked  at  be 


726 


SENSE  OF  SIGHT. 


[CHAP.  XIX. 


green,  the  retina  being  tired  of  green  rays,  receives  a  red  image 
when  the  eye  is  turned  to  a  white  object.  And  so  with  the  other 
colours  ;  the  retina  while  fatigued  by  yellow  rays  will  suppose  an 
object  to  be  violet,  and  vice  versa;  the  size  and  shape  of  the 
spectrum  corresponding  with  the  size  and  shape  of  the  original 
object  looked  at.  The  colours  which  thus  reciprocally  excite  each 
other  in  the  retina  are  those  placed  at  opposite  points  of  the  circle 
in  fig.  384.     The  peripheral  parts  of  the  retina  have  no  perception 


red 


Fig.  384. — Diagram  of  the  various  simple  and  compound  colours  of  light,  and  those  which  are 
' complement al  of  each  other,  i.e.,  which,  when  mixed,  produce  a  neutral  grey  tint.  The 
three  simple  colours,  red,  yellow,  and  blue,  are  placed  at  the  angles  of  an  equilateral 
triangle ;  which  are  connected  together  by  means  of  a  circle ;  the  mixed  colours,  green, 
orange,  and  violet,  are  placed  intermediate  between  the  corresponding  simple  or  homo- 
geneous colours ;  and  the  complemental  colours,  of  which  the  pigments,  when  mixed, 
would  constitute  a  grev,  and  of  which  the  prismatic  spectra  would  together  produce 
a  white  light,  mil  be  found  to  be  placed  in  each  case  opposite  to  each  other,  but  con- 
nected by  a  line  passing  through  the  centre  of  the  circle.  The  figure  is  also  useful  in 
showing  the  further  shades  of  colour  which  are  complementary  of  each  other.  If  the 
circle  be  supposed  to  contain  every  transition  of  colour  between  the  six  marked  down, 
those  which,  when  united,  yield  a  white  or  grey  colour,  will  always  be  found  directly 
opposite  to  each  other  ;  thus,  for  example,  the  intermediate  tint  between  orange  and 
red  is  complemental  of  the  middle  tint  between  green  and  blue. 

of  red.     The  area  of  the  retina  which  is  capable  of  receiving  im- 
pressions of  colour  is  slightly  different  for  each  colour. 

Colour  Blindness  or  Daltonism. — Daltonism  or  colour-blind- 
ness is  a  by  no  means  uncommon  visual  defect.  One  of  the  com- 
monest forms  is  the  inability  to  distinguish  between  red  and  green. 
The  simplest  explanation  of  such  a  condition  is,  that  the  elements 
of  the  retina  which  receive  the  impression  of  red,  etc.,  are  absent, 
or  very  imperfectly  developed,  or,  according  to  the  other  theory, 
that  the  red-green  substance  is  absent  from  the  retina.  Other 
varieties  of  colour  blindness  in  which  the  other  colour-perceiving 
elements  are  absent  have  been  shown  to  exist  occasionally. 


Of  the  Reciprocal  Action  of  Different  Parts  of  the  Retina 

on  each  other. 

Although  each  elementary  part  of  the  retina  represents  a  distinct 


(hap.  xix.]  RECIPROCAL  ACTION   OF    RETINA.  727 

portion  of  the  field  of  vision,  vet  the  different  elementary  parts,  or 
sensitive  points  of  that  membrane,  have  a  certain  influence  on  each 
other  ;  the  particular  condition  of  one  influencing  that  of  another, 
so  that  the  image  perceived  by  one  part  is  modified  by  the  image 
depicted  in  the  other.  The  phenomena  which  result  from  this 
relation  between  the  different  parts  of  the  retina,  may  be  arranged 
in  two  classes  ;  the  one  including  those  where  the  condition  exist- 
ing in  the  greater  extent  of  the  retina  is  imparted  to  the  remainder 
of  that  membrane;  the  other,  consisting  of  those  in  which  the 
condition  of  the  larger  portion  of  the  retina  excites,  in  the  less 
extensive  portion,  the  opposite  condition. 

1.  When  two  opposite  impressions  occur  in  contiguous  parts  of 
an  image  on  the  retina,  the  one  impression  is,  under  certain  cir- 
cumstances, modified  by  the  other.  If  the  impressions  occupy 
each  one-half  of  the  image,  this  does  not  take  place ;  for  in  that 
case  their  actions  are  equally  balanced.  But  if  one  of  the  impres- 
sions occupies  only  a  small  part  of  the  retina,  and  the  other  the 
greater  part  of  its  surface,  the  latter  may,  if  long  continued,  extend 
its  influence  over  the  whole  retina,  so  that  the  opposite  less  exten- 
sive impression  is  no  longer  perceived,  and  its  place  becomes 
occupied  by  the  same  sensation  as  the  rest  of  the  field  of  vision- 
Thus,  if  we  fix  the  eye  for  some  time  upon  a  strip  of  coloured 
paper  lying  upon  a  white  surface,  the  image  of  the  coloured  object, 
especially  when  it  falls  on  the  lateral  parts  of  the  retina,  will 
gradually  disappear,  and  the  white  surface  be  seen  in  its  place. 

2.  In  the  second  class  of  phenomena,  the  affection  of  one  part 
of  the  retina  influences  that  of  another  part,  not  in  such  a  manner 
as  to  obliterate  it,  but  so  as  to  cause  it  to  become  the  contrast  or 
opposite  of  itself.  Thus  a  grey  spot  upon  a  white  ground  appears 
darker  than  the  same  tint  of  grey  would  do  if  it  alone  occupied 
the  whole  field  of  vision,  and  a  shadow  is  always  rendered  deeper 
when  the  light  which  gives  rise  to  it  becomes  more  intense,  owing 
to  the  greater  contrast. 

The  former  phenomena  ensue  gradually,  and  only  after  the 
images  have  been  long  fixed  on  the  retina ;  the  latter  are  instan- 
taneous in  their  production,  and  are  permanent. 

In  the  same  way,  also,  colours  may  be  produced  by  contrast. 
Thus,  a  very  small  dull  grey  strip  of  paper,  lying  upon  an  extensive 
surface  of  any  bright  colour,  does  not  appear  grey,  but  has  a  faint 


728 


SEXSE   OF   SIGHT, 


[CHAP.   XIX. 


tint  of  the  colour  which  is  the  complement  of  that  of  the  surround- 
ing surface.  A  strip  of  grey  paper  upon  a  green  field,  for  example, 
often  appeai-s  to  have  a  tint  of  red,  and  when  lying  upon  a  red 
surface,  a  greenish  tint ;  it  has  an  orange-coloured  tint  upon  a 
bright  blue  surface,  and  a  bluish  tint  upon  an  orange-coloured 
surface ;  a  yellowish  colour  upon  a  bright  violet,  and  a  violet  tint 
upon  a  bright  yellow  surface.  The  colour  excited  thus,  as  a  con- 
trast to  the  exciting  colour,  being  wholly  independent  of  any  rays 
of  the  corresponding  colour  acting  from  without  upon  the  retina, 


Fig.  385. — Diagram  of  the  axes  of  rotation  to  the  eye.    The  thin  lines  indicate  axes  of  rota- 
tion, the  thick  the  position  of  muscular  attachment.    (Modified  from  Fick.) 

must  arise  as  an  opposite  or  antagonistic  condition  of  that  mem- 
brane ;  and  the  opposite  conditions  of  which  the  retina  thus  be- 
comes the  subject  would  seem  to  balance  each  other  by  their 
reciprocal  reaction.  A  necessary  condition  for  the  production  of 
the  contrasted  colours  is,  that  the  part  of  the  retina  in  which  the 
new  colour  is  to  be  excited,  shall  be  in  a  state  of  comparative 
repose  ;  hence  the  small  object  itself  must  be  grey.  A  second 
condition  is,  that  the  colour  of  the  surrounding  surface  shall  be 
very  bright,  that  is,  it  shall  contain  much  white  light. 

Movements  of  the  Eye. — The  eyeball  possesses  movement 


.  h  vi-.  xix.  J  SIMULTANEOUS  ACTION   OP   EYEa  729 

around  three  axes  indicated  in  tig.  385,  viz.,  an   antero-] 

rticitl.  and  a  transverse,   p— »"»g  through  a  centre  of  rotation 
a  little  behind  the  centre  of  the  optic  axis.    The  movement* 
accomplished  by  pain  of  muscles. 

Movements.  By  what  muscles  aceom\  lished. 

Inwards  .  .  Internal  rectus. 

Outwards    .....         External  rectus. 

C  Superior  rectus. 
*  I   Interior  oblique. 


(  Inferior  rectus. 
(  Superior  oblique. 

,  Internal  and  superior  rectus. 

Inwards  and  upwards         .  .       •    T    ~    .        1V 

r  1  Inferior  oblique. 

1  Internal  and  inferior  rectus. 

1  Superior  oblique. 

1  External  and  superior  rectus. 
Outwards  and  upwards  .       j  ^^  oblique 

1  External  and  inferior  rectus. 
1  Superior  oblique. 


Downw 


Inwards  and  downwards 


Outwards  and  downwards 


Of  the  Simultaneous  Action  of  the  two  Eyes. 

Although  the  sense  of  sight  is  exercised  by  two  organs,  yet 
the  impression  of  an  object  conveyed  to  the  mind  is  single. 
Various  theories  have  been  advanced  to  account  for  this  pheno- 
menon. By  Gall  it  was  supposed  that  we  do  not  really  employ 
both  eyes  simultaneously  in  vision,  but  always  see  with  only  one 
at  a  time.  This  especial  employment  of  one  eye  in  vision  certainly 
occurs  in  persons  whose  eyes  are  of  very  unequal  focal  distance, 
but  in  the  majority  of  individuals  both  eyes  are  simultaneously 
in  action,  in  the  perception  of  the  same  object  :  this  is  shown  by 
the  double  images  seen  under  certain  conditions.  If  two  fingers  be- 
held up  before  the  eyes,  one  in  front  of  the  other,  and  vision  be 
directed  to  the  more  distant,  so  that  it  is  seen  singly,  the  nearer 
will  appear  double  ;  while,  if  the  nearer  one  be  regarded,  the  most 
distant  will  be  seen  double  :  and  one  of  the  double  images  in 
each  case  will  be  found  to  belong  to  one  eye,  the  other  to  the 
other  eye. 

Diplopia. — Single  vision  results  only  when  certain  parts  of  the 


73° 


SENSE  OF  SIGHT. 


[chap.  XIX. 


two  retinae  are  affected  simultaneously  ;  if  different  parts  of  the 
retinae  receive  the  image  of  the  object,  it  is  seen  double.  This 
may  be  readily  illustrated  as  follows  : — The  eyes  are  fixed  upon 
some  near  object,  and  one  of  them  is  pressed  by  the  thumb  so  as 
to  be  turned  slightly  in  or  out ;  two  images  of  the  object  (Diplopia 
or  Double  Vision)  are  at  once  perceived,  just  as  is  frequently  the 
case  in  persons  who  squint.  This  diplopia  is  due  to  the  fact  that 
the  images  of  the  object  do  not  fall  on  corresponding  points  in  the 
two  retinae. 

The  parts  of  the  retinae  in  the  two  eyes  which  thus  correspond 
to  each  other  in  the  property  of  referring  the  images  which  affect 
them  simultaneously  to  the  same  spot  in  the  field  of  vision,  are, 

in  man,  just  those  parts  which 
would  correspond  to  each 
other,  if  one  retina  were  placed 
exactly  in  front  of,  and  over 
the  other  (as  in  fig.  386,  c). 
Thus,  the  outer  lateral  portion 
of  one  eye  corresponds  to,  or, 
to  use  a  better  term,  is  iden 
tical  with  the  inner  portion  of 
the  other  eye  •  or  a  of  the  eye  a  (fig.  386),  with  a'  of  the  eye  b. 
The  upper  part  of  one  retina  is  also  identical  with  the  upper  part 

of  the  other ;  and  the  lower 
parts  of  the  two  eyes  are 
identical  with  each  other. 

This  is  proved  by  a  simple 
experiment.  Pressure  upon 
any  part  of  the  ball  of  the 
eye,  so  as  to  affect  the  retina, 
produces  a  luminous  circle, 
seen  at  the  opposite  side  of 
the  field  of  vision  to  that  on 
which  the  pressure  is  made. 
If,  now,  in  a  dark  room,  we 
press  with  the  finger  at  the 
upper  part  of  one  eye,  and  at 
the  lower  part  of  the  other, 
two  luminous  circles  are  seen,   one    above   the   other  :    so,  also, 


Fig.  386. 


Fig.  387. 


CHAP.  xix.  ] 


DirLoriA. 


73i 


two    figures    are    Been    when    pressure    is    made   simultaneously 

on    the    two  outer  or   the   two    inner   Bides  of    both    eyes.      It 

is  certain,  therefore,  that  neither  the  upper  part  of  one  retina 

and  the  lower  part  of  the  other  are  identical,  nor  the  outer  lateral 

parts  of  the  two  retime,  nor  their  inner  lateral  portions.     But  if 

pressure  l>e  made  with  the  fingers  upon  both  eyes  simultaneously 

at  their  lower  part,  one  luminous  ring  is  seen  at  the  middle  of  the 

upper  part  of  the  field  of  vision ;  if  the  pressure  be  applied  to  the 

upper  part  of  both  eyes  a  single  luminous  circle  is  seen  in  the 

middle  of  the  field  of  vision  below.     So,  also,  if  we  press  upon  the 

outer  side  a  of  the  eye  a, 

and  upon  the  inner  side 

a  of  the  eye  b,  a  single 

spectrum    is    produced, 

and  is  apparent  at  the 

extreme    right    of    the 

field  of  vision  ;   if  upon 

the  point  b  of  one  eye, 

and  the  point  V  of  the 

other,  a  single  spectrum 

is   seen  to  the  extreme 

left. 

The  spheres  of  the 
two  retina)  may,  there- 
fore, be  regarded  as  lying 
one  over  the  other,  as 
in   c,   fig.  386  ;   so  that 

the  left  portion  of  one  eye  lies  over  the  identical  left  portion  of  the 
other  eye,  the  right  portion  of  one  eye  over  the  identical  right  portion 
of  the  other  eye  ;  and  with  the  upper  and  lower  portions  of  the  two 
eyes,  a  lies  over  a',  b  over  b',  and  c  over  c'.  The  points  of  the  one 
retina  intermediate  between  a  and  c  are  again  identical  with  the 
corresponding  points  of  the  other  retina  between  a'  and  c' ;  those 
between  b  and  c  of  the  one  retina,  with  those  between  b  and  c'  of 
the  other.  If  the  axes  of  the  eyes,  a  and  b  (fig,  388),  be  so  directed 
that  they  meet  at  a,  an  object  at  a  will  be  seen  singly,  for  the 
point  a  of  the  one  retina,  and  a'  of  the  other,  are  identical.  So, 
also,  if  the  object  ft  be  so  situated  that  its  image  falls  in  both  eyes 
at  the  same  distance  from  the  central  point  of  the  retina, — namely, 


Tier. 


732  SEXSE   OF   SIGHT.  [chap.  xix. 

at  b  in  the  one  eye,  and  at  b'  in  the  other, — /3  will  be  seen  single, 
for  it  affects  identical  parts  of  the  two  retinae.  The  same  will 
apply  to  the  object  y. 

In  quadrupeds,  the  relation  between  the  identical  and  non-identical  parts 

of  the  retina  cannot  be  the  same  as  in  man ;  for  the  axes  of  their  eyes 

generally  diverge,  and  can  never  be  made  to  meet  in  one  point  of  an  object. 

When  an  animal  regards  an  object  situated  directly 

in  front  of  it,  the  image  of  the  object  must  fall,  in 

both  eyes,  on  the  outer  portion  of  the  retinas.   Thus, 

the  image  of  the  object  a  (fig.  389)  will  fall  at  a'  in 

one,  and  at  a"  in  the  other  :  and  these  points  a'  and 

a"  must    be   identical.      So,  also,  for  distinct   and 

single  vision  of  objects,  b  or  e,  the  points  V  and  b" 

or  c'  e",  in  the  two  retinae,  on  which  the  images  of 

these  objects  fall,  must  be  identical.     All  points  of 

the  retina  in  each  eye  which  receive  rays  of  light 

K"'  j89-  from  lateral  objects  only,  can  have  no  corresponding 

identical  points  in  the  retina  of  the  other  eye  ;  for 

otherwise  two  objects,  one  situated  to  the  right  and  the  other  to  the  left, 

would  appear  to  lie  in  the  same  spot  of  the  field  of  vision.     It  is  probable, 

therefore,  that  there  are  in  the  eyes  of  animals,  parts  of  the  retinas  which 

are  identical,  and  parts  which  are  not  identical,  i.e..  parts  in  one  which 

have  no  corresponding  parts  in  the  other  eye.     And  the  relation  of  the  two 

retinas  to  each  other  in  the  field  of  vision  may  be  represented  as  in  fig.        . 


Binocular  Vision — The  cause  of  the  impressions  on  the 
identical  points  of  the  two  retime  giving  rise  to  but  one  sensation, 
and  the  perception  of  a  single  image,  must  either  lie  in  the 
structural  organisation  of  the  deeper  or  cerebral  portion  of  the 
visual  apparatus,  or  be  the  result  of  a  mental  operation  ;  for  in 
no  other  case  is  it  the  property  of  the  corresponding  nerves  of  the 
two  sides  of  the  body  to  refer  their  sensations  as  one  to  one 
spot. 

Many  attempts  have  been  made  to  explain  this  remarkable 
relation  between  the  eyes,  by  referring  it  to  anatomical  relation 
between  the  optic  nerves.  The  circumstance  of  the  inner  portion 
of  the  fibres  of  the  two  optic  nerves  decussating  at  the  commis- 
sure, and  passing  to  the  eye  of  the  opposite  side,  while  the 
outer  portion  of  the  fibres  continue  their  course  to  the  eye  of 
the  same  side,  so  that  the  left  side  of  both  retinas  is  formed 
from  one  root  of  the  nerves,  and  the  right  side  of  both  retinae 
from  the  outer  root,  naturally  led  to  an  attempt  to  explain 
the  phenomenon  by  this  distribution  of  the  fibres  of  the  nerves. 


ohap.  xix.]  BINOCULAB   VISION.  733 

And  this  explanation  is  favoured  by  cases  in  which  the  entire  of 
one  side  of  the  retina,  as  far  as  the  central  point  in  both  eyeB, 
sometimes  becomes  insensible.  Bui  Mailer  shows  the  inadequate- 
ness  of  this  theory  to  explain  the  phenomenon,  unless  it  he  supposed 
that  each  fibre  in  each  cerebral  portion  of  the  optic  nerves  divides 
in  the  optic  commissure  into  two  branches  for  the  identical  points 
of  the  two  retinae,  as  is  shown  in  A,  fig.  390.  But  there  is 
no  foundation  for  such  supposition. 

By  another  theory  it  is  assumed  that  eaeli  optic  nerve  contains 
exactly  the  same  number  of  fibres  as  the  other,  and  that  the  corre- 
sponding fibres  of  the  two  nerves  are  united  in  the  Sensorium  (as  in 


a\\b         a//])' 


Fig.  390. 

fig.  390,  B).  But  in  this  theory  no  account  is  taken  of 
the  partial  decussation  of  the  fibres  of  the  nerves  in  the  optic 
commissure. 

According  to  a  third  theory,  the  fibres  a  and  a,  fig.  390,  G, 
coming  from  identical  points  of  the  two  retinae,  are  in  the  optic 
commissure  brought  into  one  optic  nerve,  and  in  the  brain  either 
are  united  by  a  loop,  or  spring  from  the  same  point.  The  same 
disposition  prevails  in  the  case  of  the  identical  fibres  b  and  b'. 
According  to  this  theory,  the  left  half  of  each  retina  would  be 
represented  in  the  left  hemisphere  of  the  brain,  and  tlie  right  half 
of  each  retina  in  the  right  hemisphere. 

Another  explanation  is  founded  on  the  fact,  that  at  the  anterior 
part  of  the  commissure  of  the  optic  nerve,  certain  fibres  pass 
across  from  the  distal  portion  of  one  nerve  to  the  corresponding 
portion  of  the  other  nerves,  as  if  they  were  commissural  fibres 
forming  a  connection  between  the  retinae  of  the  two  eyes.     It  is 


734 


SENSE   OF   SIGHT. 


[chap.  XIX. 


supposed,  indeed,  that  these  fibres  may  connect  the  corresponding 
pans  of  the  "two  retinae,  and  may  thus  explain  their  unity  of 
action ;  in  the  same  way  that  corresponding  parts  of  the  cerebral 
hemispheres  are  believed  to  be  connected  together  by  the  comis- 
sural  fibres  of  the  corpus  callosum,  and  so  enabled  to  exercise  unity 
of  function. 

Judgment  of  Solidity.— On  the  whole,  it  is  probable,  that 
the  power  of  forming  a  single  idea  of  an  object  from  a  double 
impression  conveyed  by  it  to  the  eyes  is  the  result  of  a  mental 
act.  This  view  is  supported  by  the  same  facts  as  those  employed 
by  Wheatstone  to  show  that  this  power  is  subservient  to  the 
purpose  of  obtaining  a  right  perception  of  bodies  raised  in  relief. 
"When  an  object  is  placed  so  near  the  eyes  that  to  view  it  the  optic 
axes  must  converge,  a  different  perspective  projection  of  it  is  seen 
by  each  eye.  these  perspectives  being  more  dissimilar  as  the 
convergence  of  the  optic  axes  becomes  greater.  Thus,  if  any 
figure  of  three  dimensions,  an  outline  cube,  for  example,  be  held 


Yis.  511. 

at  a  moderate  distance  before  the  eyes,  and  viewed  with  each 
eye  successively  while  the  head  is  kept  perfectly  steadv,  a  (fig. 
391)  will  be  the  picture  presented  to  the  right  eye,  and  b  that 
seen  by  the  left  eye.  Wheatstone  has  shown  that  on  this 
circumstance  depends  in  a  great  measure  our  conviction  of  the 
solidity  of  an  object,  or  of  its  projection  in  relief.  If  different 
perspective  drawings  of  a  solid  body,  one  representing  the  image 
seen  by  the  right  eye,  the  other  that  seen  by  the  left  (for 
example,  the  drawing  of  a  cube,  a,  b,  fig.  391),  be  presented  to 
corresponding  parts  of  the  two  retina,  as  may  be  readily  done 
by  means  of  the  stereoscope,  the  mind  will  perceive  not  merely  a 
single  representation  of  the  object,  but  a  body  projecting  in  relief, 
the  exact  counterpart  of  that  from  which  the  drawings  were  made. 


CHAP,  xix.]  JUDGMENT   OF   SOLIDITY. 


735 


By  transposing   two  stereoscopic   pictures  a  reverse   effect    is 
produced:    the   elevated    parts    appear    to    be   depressed,  and 

An   instrument  contrived  with  this  purpose  is  termed  a 
loscope.     Viewed  with  this  instrument  a  bust  app 

hollow  mask,  and   as   may  readily  be   imagined   the  effect  is  most 


bewildering. 


73^. 


GENERATION  AND   DEVELOPMENT. 


[CHA1>.   XX. 


CHAPTER    XX 

GENERATION    AND    DEVELOPMENT. 

The  several  organs  and  functions  of  the  human  body  which 
have  been  considered  in  the  previous  chapters,  have  relation  to 
the  individual  being.  "We  have  now  to  consider  those  organs  and 
functions  which  are  destined  for  the  propagation  of  the  species. 
These  comprise  the  several  provisions  made  for  the  formation, 
impregnation,  and  development  of  the  ovum,  from  which  the 
embryo  or  foetus  is  produced  and  gradually  perfected  into  a  fully- 
formed  human  being. 


Fig.  392. — Diagrammatic  view  of  the  uterus  and  its  appendages,  as  seen  from  behind.  The 
uterus  and  upper  part  of  the  vagina  have  heen  laid  open  by  removing  the  posterior 
wall ;  the  Fallopian  tube,  round  ligament,  and  ovarian  ligament  have  been  cut  short, 
and  the  broad  ligament  removed  on  the  left  side;  v,  the  upper  part  of  the  uterus  ;  <•, 
the  cervix  opposite  the  os  intermim ;  the  triangular  shape  of  the  uterine  cavity  is 
shown,  and  the  dilatation  of  the  cervical  cavity  with  the  rugee  termed  arbor  vitfe  ;  v, 
upper  part  of  the  vagina  ;  od,  Fallopian  tube  or  oviduct ;  the  narrow  communication 
of  its  cavity  with  that  of  the  cornu  of  the  uterus  on  each  side  is  seen  ;  I,  round  liga- 
ment :  lo,  ligament  of  the  ovary ;  o,  ovary ;  /.  wide  outer  part  of  the  right  Fallopian 
tube  ;  fi,  its  fimbriated  extremity ;  jjo,  parovarium  ;  h,  one  of  the  hydatids  frequently 
found  connected  with  the  broad  ligament,    i.     (Allen  Thomson.) 

The    organs   in    the   two    sexes    concerned   in    effecting   these 
objects  are  named  the  Generative  organs,  or  Sexual  apparatus. 


Generative  Organs  of  the  Female. 

The   female    organs    of  generation    (fig.    392)    consist    of  two 
Ovaries,  whose  function  is  the  formation  of  ova ;  of  a  Fallopian 


CHAP.  XX.] 


OVARIES. 


757 


tub?,  or  oviduct,  connected  with  each  ovary,  for  the  purpose  of 
conducting  the  ovum  from  the  ovary  to  the  Uterus  or  cavity  in 
which,  if  impregnated,  it  is  retained  until  the  embryo  is  fully 

developed,  and  fitted  to  maintain  its  existence  independently  of 
internal  connection  with  the  parent ;  and,  lastly,  of  a  canal,  or 
Vagina,  with  its  appendages,  for  the  reception  of  the  male  gene- 
rative organs  in  the  act  of  copulation,  and  for  the  subsequent 
discharge  of  the  foetus. 

Ovaries. — The  ovaries  are  two  oval  compressed  bodies,  situated 
in  the  cavity  of  the  pelvis,  one  on  each  side,  enclosed  in  the  folds 
of  the  broad  ligament.     Each  ovary  measures  about  an  inch  and 


fm^ 


a  rap 


-  '^--  . '  ';^» 


^  d 


^o-  393- — Pietfl  o/  '7  section  of  the  prepared  ovary  of  the  cat.  i,  outer  covering-  and  free 
border  of  the  ovary  ;  i',  attached  border  ;  2,  the  ovarian  stroma,  presenting  a  fibrous 
and  vascular  structure ;  3,  granular  substance  lying  external  to  the  fibrous  stroma; 
4,  blood-vessels  ;  5,  ovigenns  in  their  earliest  stages  occupying  a  part  of  the  granular 
layer  near  the  surface ;  6,  ovigerms  which  have  begun  to  enlarge  and  to  pass  more 
deeply  into  the  ovary ;  7,  ovigenns  round  which  the  Graafian  follicle  and  tunica 
granulosa  are  now  formed,  and  which  have  passed  somewhat  deeper  into  the  ovary  and 
are  surrounded  by  the  fibrous  stroma ;  8,  more  advanced  Graafian  follicle  with  the 
ovum  imbedded  in  the  layer  of  cells  constituting  the  proligerous  disc  ;  9,  the  most 
advanced  follicle  containing  the  ovum,  &c.  ;  9',  a  follicle  from  which  the  ovum  has 
accidentally  escaped  ;  10,  corpus  luteum.     ^.     (Schron.) 


a  half  in  length,  three- quarters  of  an  inch  in  width,  and  nearly 
half  an  inch  in  thickness,  and  is  attached  to  the  uterus  by  a 
narrow  fibrous  cord  (the  ligament  of  the  ovary),  and,  more 
slightly,  to  the  Fallopian  tubes  by  one  of  the  fimbria)  into  which 
the  walls  of  the  extremity  of  the  tube  expand. 

Structure. — The  ovary  is  enveloped  by  a  capsule  of  dense  fibro- 
cellular  tissue,  covered  on  the  outside  by  epithelium  (germ-epithe- 
lium), the  cells  of  which,  although  continuous  with,  and  originally 

3  B 


733 


GENERATION  AND  DEVELOPMENT. 


[CHAP.  XX. 


derived  from,  the  squamous  epithelium  of  the  peritoneum,    are 
short  columnar. 

The  term  germ-epithelium,  is  used  on  account  of  the  relation  which  it 
bears  in  early  life  to  the  development  of  the  ova  ;  the  ova  being  formed  by- 
certain  of  these  epithelial  cells,  which,  becoming  modified  in  structure,  are 
gradually  enclosed  in  the  ovarian  stroma.     (Waldeyer.)     (See  fig.  394.) 

The  internal  structure  of  the  organ  consists  of  a  peculiar  soft 
fibrous  tissue,  or  stroma,  abundantly  supplied  with  blood-vessels, 

and  having  em- 
bedded in  it,  in 
various  stages  of 
development,  nu- 
erous  minute 
Hides  or  vesi- 
cles, the  Graafian 


human  ovary  be 
examined  at  any 
period      between 

pigi  -^—Section  of  the  ovary  of  a  cat.    A,  germinal  epithelium:      early  mtailCy  and 

C  B,  immature  Graafian  follicle  ;  C,  stroma  of  ovary  ;  D.vitel-      QJ_rQ_norl  on.0  i,,,+ 

line  membrane  containing  the  ovum ;  E,  Graafian  follicle      ad\  anced  age,  but 

S^ut^.^^f0^tomWW<ihtheOVmahaa    specially  during 

that  period  of  life 
in  which  the  power  of  conception  exists,  it  will  be  found  to  contain 
a  number  of  small  vesicles  or  membranous  sacs  of  various  sizes ; 
these  have  been  already  alluded  to  as  the  follicles  or  vesicles  of  De 
Graaf,  the  anatomist  who  first  accurately  described  them ;  they 
are  sometimes  called  ovisacs. 

At  their  first  formation,  the  Graafian  vesicles  are  near  the 
surface  of  the  stroma  of  the  ovary,  but  subsequently  become  more 
deeply  placed ;  and,  again,  as  they  increase  in  size,  make  their 
way  towards  the  surface  (fig.  394)- 

When  mature,  they  form  little  prominences  on  the  exterior  of 
the  ovary,  covered  only  by  a  thin  layer  of  condensed  fibrous  tissue 
and  epithelium.     Each  follicle  has  an  external  membranous  enve- 


i-iiAi-.  xx.]  STEUCTUEE   OP  THE  OVUM.  730 

lope,  comprised  of  fine  fibrous  tissue,  and  connected  with  the  sur- 
rounding stroma  of  the  ovary  by  networks  of  blood-vessels.  This 
envelope  or  tunic  is  lined  with  a  layer  of  nucleated  cells,  forming 
a  kind  of  epithelium  or  internal  tunic,  and  named  membrana  gra- 
nulosa. The  cavity  of  the  follicle  is  filled  with  an  albuminous 
fluid  in  which  microscopic  granules  float ;  and  it  contains  also  the 

OVUul. 

Ovum. — The  ovum  is  a  minute  spherical  body  situated,  in  im- 
mature follicles,  near  the  centre;  but  in  those  nearer  maturity,  in 
contact  with  the  membrana  granulosa  at  that  part  of  the  follicle 
which  forms  a  prominence  on  the  surface  of  the  ovary.  The  cells 
of  the  ineinbranu-granuloso  are  at  that  point  more  numerous  than 
elsewhere,  and  are  heaped  around  the  ovum,  forming  a  kind  of 
granular  zone,  the  discus  proligerus  (fig.  395,). 

In  order  to  examine  an  ovum,  one  of  the  Graafian  ve.-icles,  it  matters 
not  whether  it  be  of  small  size  or  arrived  at  maturity,  should  be  pricked, 
and  the  contained  fluid  received  upon  a  slide.  The  ovum  then. 
being  found  in  the  midst  of  the  fluid  by  means  of  a  >imple  lens,  mav  be 
further  examined  with  higher  microscopic  powers.  Owing  to  its  globular 
form,  however,  its  structure  cannot  be  seen  until  it  is  subjected  to  o-entle 
pressure. 

The  human  ovum  measures  about  -3-^  of  an  inch.  Its  external 
investment  is  a  transparent  membrane,  about  *  of  an  inch  in 
thickness,  which  under  the  microscope  appears 
as  a  bright  ring  (4,  fig.  395),  bounded  exter- 
nally and  internally  by  a  dark  outline  ;  it  is 
called  the  zona  pellucida,  or  vitelline  mem- 
brane. It  adheres  externally  to  the  heap  of 
cells  constituting  the  dlscux  proligerus.  Within 
this  transparent  investment  or  zona  pellucida, 
and  usually  in  close  contact  with  it,  lies  the 
yolk  or  vitellus,  which  is  composed  of  granules  '"i.germinai'spot; 

,      ,    ,      ,  c  .  .  •     i      i  i     i    •  2-  germinal  vesicle ;  3, 

and  globules  01  various  sizes,  imbedded  in  a  yolk ;  4.  zona  peiiu- 
more   or  less  fluid  substance.      The  smaller        genu;     6,    adherent 

,  l-i  ,1  granules       or      cells. 

granules,  which  are  the  more  numerous,  re-         (Bai: 
semble  in  their  appearance,  as  well  as  their 
constant  motion,  pigment-granules.    The  larger  granules  or  globules, 
which  have  the  aspect  of  fat-globules,  are  in  greatest  number  at 
the  periphery  of  the  yolk    The  number  of  the  granules  is,  according 

3  B  2 


740  GENERATION  AND   DEVELOPMENT.  [chap.  xx. 

to  BischofF,  greatest  in  the  ova  of  carnivorous  animals.  In  the 
human  ovum  their  quantity  is  comparatively  small. 

In  the  substance  of  the  yolk  is  imbedded  the  germinal  vesicle, 
or  vesicula  germinativa  (2,  fig.  395).  This  vesicle  is  of  greatest 
relative  size  in  the  smallest  ova,  and  is  in  them  surrounded 
closely  by  the  yolk,  nearly  in  the  centre  of  which  it  lies.  During 
the  development  of  the  ovum,  the  germinal  vesicle  increases  in 
size  much  less  rapidly  than  the  yolk,  and  comes  to  be  placed  near 
to  its  surface.  It  is  about  yf-^  of  an  inch  in  diameter.  It  consists 
of  a  fine,  transparent,  structureless  membrane,  containing  a  clear, 
watery  fluid,  in  which  are  sometimes  a  few  granules  ;  and  at  that 
part  of  the  periphery  of  the  germinal  vesicle  which  is  nearest  to 
the  pertphery  of  the  yolk  is  situated  the  germinal  spot  (macula 
germinativa),  a  finely  granulated  substance,  of  a  yellowish  colour, 
strongly  refracting  the  rays  of  light,  and  measuring  about  -3^00  of 
an  inch  in  diameter. 

.Such  are  the  parts  of  which  the  Graafian  follicle  and  its  contents, 
including  the  ovum,  are  composed.  With  regard  to  the  mode  and 
order  of  development  of  these  parts  there  is  considerable  uncer- 
tainty j  but  it  seems  most  likely  that  the  ovum  is  formed  before 
the  Graafian  vesicle  or  ovisac. 

With  regard  to  the  parts  of  the  ovum  first  formed,  it  appears 
certain  that  the  formation  of  the  germinal  vesicle  precedes  that 
of  the  yolk  and  zona  pellucida,  or  vitelline  membrane.  Whether 
the  germinal  spot  is  formed  first,  and  the  germinal  vesicle  after- 
wards developed  around  it,  cannot  be  decided  in  the  case  of  verte- 
brate animals  ;  but  the  observations  of  Kolliker  and  Bagge  on  the 
development  of  the  ova  of  intestinal  worms  show  that  in  these 
animals,  the  first  step  in  the  j)rocess  is  the  production  of  round 
bodies  resembling  the  germinal  spots  of  ova,  the  germinal  vesicles 
being  subsequently  developed  around  these  in  the  form  of  trans- 
parent membranous  cells. 

From  the  earliest  infancy,  and  through  the  whole  fruitful 
period  of  life,  there  appears  to  be  a  constant  formation,  develop- 
ment, and  maturation  of  Graafian  vesicles,  with  their  contained 
ova.  Until  the  period  of  puberty,  however,  the  process  is  com- 
paratively inactive  :  for,  previous  to  this  period,  the  ovaries  are 
small  and  pale,  the  Graafian  vesicles  in  them  are  very  minute, 
and  probably  never  attain  full  development,  but  soon  shrivel  and 


chap,  xx.]  s'l'UUCTUItE   OF    [JTEEUS.  yji 

disappear,  instead,  of  bursting,  as  matured  follicles  do;  the  con- 
tained ova  are  also  incapable  of  being  impregnated.  But,  coinci- 
dent with  the  other  changes  which  occur  in  the  body  at  the  time 
of  puberty,  the  ovaries  enlarge,  and  become  very  vascular,  the 
formation  of  Graafian  vesicles  is  more  abundant,  the  size  aud 
degree  of  development  attained  by  them  are  greater,  and  the  ova 
are  capable  of  being  fecundated. 

Fallopian  Tubes. — The  Fallopian  tubes  are  about  four  inches 
in  length,  and  extend  between  the  ovaries  and  the  upper  angles 
of  the  uterus.  At  the  point  of  attachment  to  the  uterus,  the 
Fallopian  tube  is  very  narrow;  but  in  its  course  to  the  ovary  it 
increases  to  about  a  line  and  a  half  in  thickness  ;  at  its  distal 
extremity,  which  is  free  and  floating,  it  bears  a  number  otjiiubrif, 
one  of  which,  longer  than  the  rest,  is  attached  to  the  ovary.  The 
canal  by  which  each  Fallopian  tube  is  traversed  is  narrow,  espe- 
cially at  its  point  of  entrance  into  the  uterus,  at  which  it  will 
scarcely  admit  a  bristle  ;  its  other  extremity  is  wider,  and  opens 
into  the  cavity  of  the  abdomen,  surrounded  by  the  zone  of  fimbria). 
Externally,  the  Fallopian  tube  is  invested  with  peritoneum;  in- 
ternally, its  canal  is  lined  with  mucous  membrane,  covered  with 
ciliated  epithelium  :  between  the  peritoneal  and  mucous  coats,  the 
walls  are  composed,  like  those  of  the  uterus,  of  fibrous  tissue  and 
plain  muscular  fibres. 

Uterus. — The  Uterus  (u,  c,  fig.  392)  is  somewhat  pyriform, 
and  in  the  unimpregnated  state  is  about  three  inches  in  length, 
two  in  breadth  at  its  upper  part  or  fundus,  but  at  its  lower 
pointed  part  or  neck,  only  about  half  an  inch.  The  part  between 
the  fundus  and  neck  is  termed  the  body  of  the  uterus  :  it  is  about 
an  inch  in  thickness. 

Structure. — The  uterus  is  constructed  of  three  principal  layers, 
or  coats, — serous,  fibrous  and  muscular,  and  mucous.  (1.)  The 
ser<»us  coat,  which  has  the  same  general  structure  as  the  perito- 
neum, covers  the  organ  before  and  behind,  but  is  absent  from  the 
front  surface  of  the  neck.  (2.)  The  middle  coat  is  composed  of 
dense  connective  tissue,  with  which  are  intermingled  fibres  of 
unstriped  muscle.  The  latter  become  enormously  developed 
during  pregnancy.  (3.)  The  mucous  membrane  of  the  uterus 
will  be  described  more  in  detail  presently  (p.  745).  It  is  lined 
by  columnar   ciliated    epithelium,  which   extends  also    into    the 


742  GENERATION   AND   DEVELOPMENT.  [chap.  x\\ 

interior  of  the  tubular  glands,  of  which  the  mucous  membrane  is 
largely  made  up.  (Allen  Thomson,  Nylander,  Friedlander,  John 
Williams.) 

The  cavity  of  the  uterus  corresponds  in  form  to  that  of  the 
organ  itself :  it  is  very  small  in  the  unimpregnated  state  ;  the 
sides  of  its  mucous  surface  being  almost  in  contact,  and  probably 
only  separated  from  each  other  by  mucus.  Into  its  upper  part, 
at  each  side,  opens  the  canal  of  the  corresponding  Fallopian 
tube  :  below,  it  communicates  with  the  vagina  by  a  fissure-like 
opening  in  its  neck,  the  os  uteri,  the  margins  of  which  are  dis" 
tinguished  into  two  lips,  an  anterior  and  posterior.  In  the 
mucous  membrane  of  the  cervix  are  found  several  mucous 
follicles,  termed  ovula  or  glandular  Nabothi  :  they  probably  form 
the  jelly-like  substance  by  which  the  os  uteri  is  usually  found 
closed. 

The  vagina  is  a  membranous  canal,  five  or  six  inches  long, 
extending  obliquely  downwards  and  forwards  from  the  neck  of 
the  uterus,  which  it  embraces,  to  the  external  organs  of  genera- 
tion. It  is  lined  with  mucous  membrane,  which  in  the  ordinary 
contracted  state  of  the  canal  is  thrown  into  transverse  folds. 
External  to  the  mucous  membrane  the  walls  of  the  vagina  are 
constructed  of  fibrous  tissue,  within  which,  especially  around  the 
lower  part  of  the  tube,  is  a  layer  of  erectile  tissue.  The  lower 
extremity  of  the  vagina  is  embraced  by  an  orbicular  muscle,  the 
constrictor  vagince ;  its  external  orifice,  in  the  virgin,  is  partially 
closed  by  a  fold  or  ring  of  mucous  membrane,  termed  the  hymen. 
The  external  organs  of  generation  consist  of  the  clitoris,  a  small 
elongated  body,  situated  above  and  in  the  middle  line,  and  con- 
structed, like  the  male  penis,  of  two  erectile  corpora  cavernosa, 
but  unlike  it,  without  a  corpus  spongiosum,  and  not  perforated 
by  the  urethra;  of  two  folds  of  mucous  membrane,  termed  labia 
interna,  or  nymphce ;  and,  in  front  of  these,  of  two  other  folds, 
the  labia  externa,  or  pudenda,  formed  of  the  external  integument, 
and  lined  internally  by  mucous  membrane.  Between  the  nymplue 
and  beneath  the  clitoris  is  an  angular  space,  termed  the  vesti- 
bule, at  the  centre  of  whose  base  is  the  orifice  of  the  meatus 
vrinarius.  Numerous  mucous  follicles  are  scattered  beneath 
the  mucous  membrane  composing  these  parts  of  the  external 
organs  of  generation ;  and  at   the  side  of  the  lower  part  of  the 


ohap.  xx.]  DISCHABGE  OF  THE  OVUM.  743 

vagina,  are  two  larger  tabulated  glands,  named  vulvo-vaginal,  or 
Duverney'a  glands,  which  are  analogous  to  Cowper's  glands  in  the 
male. 

Discharge  of  the  Ovum. — In  the  process  of  development  <»f 
individual  Graafian  vesicles,  it  has  been  already  observed,  that  as 
each  increases  in  size,  it  gradually  approaches  the  surface  of  the 
ovary,  and  when  fully  ripe  or  mature,  forms  a  little  projection  on 
the  exterior.  Coincident  with  the  increase  of  size,  caused  by  the 
augmentation  of  its  liquid  contents,  the  external  envelope  of  the 
distended  vesicle  becomes  very  thin  and  eventually  bursts.  By 
this  means,  the  ovum  and  fluid  contents  of  the  Graafian  vesicle 
are  liberated,  and  escape  on  the  exterior  of  the  ovary,  whence  they 
pass  into  the  Fallopian  tube,  the  fimbriated  processes  of  the  ex- 
tremity of  which  are  supposed  coincidentally  to  grasp  the  ovary, 
while  the  aperture  of  the  tube  is  applied  to  the  part  corresponding 
to  the  matured  and  bursting  vesicle. 

In  animals  whose  capability  of  being  impregnated  occurs  at 
regular  periods,  as  in  the  human  subject,  and  most  Mammalia, 
the  Graafian  vesicles  and  their  contained  ova  appear  to  arrive  at 
maturity,  and  the  latter  to  be  discharged  at  such  periods  only. 
But  in  other  animals,  e.g.,  the  common  fowl,  the  formation,  matura- 
tion, and  discharge  of  ova  appear  to  take  place  almost  constantly. 

It  has  long  been  known,  that  in  the  so-called  oviparous 
animals,  the  separation  of  ova  from  the  ovary  may  take  place 
independently  of  impregnation  by  the  male,  or  even  of  sexual 
union.  And  it  is  now  established  that  a  like  maturation  and 
discharge  of  ova,  independently  of  coition,  occurs  in  Mammalia, 
the  periods  at  which  the  matured  ova  are  separated  from  the 
ovaries  and  received  into  the  Fallopian  tubes  being  indicated  in 
the  lower  Mammalia  by  the  phenomena  of  heat  or  rut :  in  the 
human  female,  although  not  always  with  exact  coincidence,  by  the 
phenomena  of  menstruation.  If  the  union  of  the  sexes  take  place, 
the  ovum  may  be  fecundated,  and  if  no  union  occur  it  perishes. 

That  this  maturation  and  discharge  occur  periodically,  and 
only  during  the  phenomena  of  heat  in  the  lower  Mammalia,  is 
made  probable  by  the  facts  that,  in  all  instances  in  which 
Graafian  vesicles  have  been  found  presenting  the  appearance  of 
recent  rupture,  the  animals  were  at  the  time,  or  had  recently 
been,  in  heat ;  that  on  the  other  hand,  there  is  no  authentic  and 


744  GENERATION  AND   DEVELOPMENT.  [chap.  xx. 

detailed  account  of  Graafian  vesicles  being  found  ruptured  in  the 
intervals  of  the  period  of  heat;  and  that  female  animals  do  not  admit 
the  males,  and  never  become  impregnated,  except  at  those  periods. 

Menstruation. — Many  circumstances  make  it  certain  that  the 
human  female  is  subject,  in  these  respects,  to  the  same  law  us  the 
females  of  other  mammiferous  animals  ;  namely,  that  in  her  as  in 
them,  ova  are  matured  and  discharged  from  the  ovary  independent 
of  sexual  union.  This  maturation  and  discharge  occur,  moreover, 
periodically  at  or  about  the  epochs  of  menstruation.  Thus 
Graafian  vesicles  recently  ruptured  have  been  frequently  seen  in 
ovaries  of  virgins  or  women  who  could  not  have  been  recently  im- 
pregnated :  and  although  it  is  true  that  the  ova  discharged  under 
these  circumstances  have  rarely  been  discovered  in  the  Fallopian 
tube,  partly  on  account  of  their  minute  size,  and  partly  because 
the  search  has  seldom  been  prosecuted  with  much  care,  yet  analogy 
forbids  us  to  doubt  that  in  the  human  female,  as  in  the  domestic 
quadrupeds,  the  result  and  purpose  of  the  rupture  of  the  follicles 
is  the  discharge  of  the  ova. 

The  evidence  of  the  periodical  discharge  of  ova  is  that  in  most 
cases  in  which  signs  of  menstruation  have  been  found  in  the 
uterus,  follicles  in  a  state  of  maturity  or  of  rupture  have  been 
seen  in  the  ovary :  and  that  although  conception  is  not  confined  to 
the  periods  of  menstruation,  yet  it  is  more  likely  to  occur  about  a 
menstrual  epoch  than  at  other  times. 

The  exact  relation  between  the  discharge  of  ova  and  men- 
struation is  not  very  clear.  It  was  generally  believed  that  the 
monthly  flux  was  the  result  of  a  congestion  of  the  uterus  arising 
from  the  enlargement  and  rupture  of  a  Graafian  follicle ;  but 
though  a  Graafian  follicle  is,  as  a  rule,  ruptured  at  each  menstrual 
epoch,  yet  several  instances  are  recorded  in  which  menstruation 
has  occurred  where  no  Graafian  follicle  has  been  ruptured,  and  on 
the  other  hand  cases  are  known  where  ova  have  been  discharged 
in  amenorrhceic  women.  It  must  therefore  be  admitted  that  men- 
struation is  not  dependent  on  the  maturation  and  discharge  of  ova. 

It  was,  moreover,  generally  understood  that  ova  were  discharged 
towards  the  close  or  soon  after  the  cessation  of  a  menstrual  flow. 
Observations  made  after  death,  and  facts  obtained  by  clinical 
investigation,  however,  do  not  support  this  view.  (Reichert, 
J.  Williams,  Lowenthal.)     Rupture  of  a  Graafian  follicle  does  not 


CHAP.XX.]  MEXSTItUATInX.  745 

happen  on  the  same  day  of  the  monthly  period  in  all  women  It 
may  occur  towards  the  close  or  soon  after  the  cessation  of  a  flow; 
but  only  in  a  small  minority  of  the  subjects  examined  after  death 
was  this  the  case.  On  the  other  hand,  in  almost  all  such  subjects 
of  which  there  is  record,  rupture  of  the  follicle  appears  to  have 
taken  place  before  the  commencement  <»f  the  catamenial  flow* 
Moreover,  the  custom  of  the  Jews — a  prolific  race,  to  whom  by 
the  Levitical  law  sexual  intercourse  during  the  week  following 
menstruation  was  forbidden — militates  strongly  in  favour  of  the 
view  that  conception  usually  occurs  before  and  not  soon  after  a 
menstrual  epoch,  and  necessarily,  therefore,  for  the  view  that  ova 
are  usually  discharged  before  the  catamenial  flow.  This,  together 
with  the  anatomical  condition  of  the  uterus  just  before  the  cata- 
nienia,  seem  to  indicate  that  the  ovum  fertilized  is  that  which  is 
discharged  in  connection  with  the  first  absent,  and  not  that  with 
the  last  present  menstruation.     (Kundrat.) 

Though  menstruation  does  not  appear  to  depend  upon  the 
discharge  of  ova,  yet  the  presence  of  the  ovaries  seems  necessary 
for  the  performance  of  the  function  ;  for  women  do  not  menstruate 
when  both  ovaries  have  been  removed  by  operation.  Some  in- 
stances have  been  recently  recorded,  indeed,  of  a  sanguineous 
discharge,  occurring  periodically  from  the  vagina  after  both 
<  -varies  have  been  previously  removed  for  disease  ;  and  it  has  been 
inferred  from  this  that  menstruation  is  a  function  independent 
of  the  ovary :  but  this  evidenee  is  not  conclusive,  inasmuch 
as  it  is  possible  that  portions  of  ovarian  tissue  were  left  after  the 
operation. 

Characters  of  Menstrual  Discharge. — The  menstrual  dis- 
charge is  a  thin  sanguineous  fluid,  having  a  peculiar  odour.  It  is 
of  a  dark  colour,  and  consists  of  blood,  epithelium,  and  mucus 
from  the  uterus  and  vagina,  serum,  and  the  debris  of  a  membrane 
called  the  decidua  menstrualis.  This  membrane  is  the  developed 
mucous  surface  of  the  body  of  the  uterus.  It  does  not  extend 
into  the  Fallopian  tube  or  iuto  the  cavity  of  the  cervix.  It  attains 
its  highest  state  of  development  in  the  unimpregnated  organ  just 
before  the  commencement  of  a  catamenial  flow  (fig.  396).  If 
impregnation  take  place,  it  becomes  the  decidua  vera;  if  impreg- 
nation fail,  the  membrane  undergoes  rapid  disintegration ;  its 
vessels  are  laid  open  and  haemorrhage  follows  (John  Williams). 


746 


GENERATION  AND   DEVELOPMENT. 


[chap.  XX. 


The  blood  poured  out  does  not  coagulate  in  consequence  partly  of 
the  admixture  already  mentioned,  or,  very  possibly,  coagulation 


Fig.  396. 


Fig-  397- 


Fig.  398. 


Fig.  396. — Diagram  of  uterus  just  before  menstruation  ;  the  shaded  portion  represents  the 
thickened  mucous  membrane.  Fig.  397. — Diagram  of  uterus  when  menstruation  has  just 
ceased,  sho\ving  the  cavity  of  the  uterus  deprived  of  mucous  membrane.  Fig.  398-~ 
Diagram  of  uterus  a  week  after  the  menstrual  flux  has  ceased :  the  shaded  portion  repre- 
sents renewed  mucous  membrane.     (J.  Williams.) 

occurs,  but  the  process  is  more  or  less  spoiled,  and  what  clot  is  formed 
is  broken  down  again,  so  as  to  imitate  liquid  blood.   (See  also  p.  91.) 

Menstruation,  therefore,  is  not  the  result  of  congestion,  or  of  a 
species  of  erection,  but  of  a  destructive  process  by  which  the 
decidua  or  nidus  prepared  for  an  impregnated  ovum  is  carried 
away.  It  is  not  a  sign  of  the  capability  of  being  impregnated  as 
much  as  of  disappointed  impregnation. 

The  occurrence  of  a  menstrual  discharge  is  one  of  the  most 
prominent  indications  of  the  commencement  of  puberty  in  the 
female  sex  ;  though  its  absence  even  for  several  years  is  not 
necessarily  attended  with  arrest  of  the  other  characters  of  this 
period  of  life,  or  with  inaptness  for  sexual  union,  or  incapability 
of  impregnation.  The  average  time  of  its  first  appearance  in 
females  of  this  country  and  others  of  about  the  same  latitude,  is 
from  fourteen  to  fifteen  ;  but  it  is  much  influenced  by  the  kind  of 


(MM-,  xx.]  CORPUS  LUTEUM.  747 

life  to  which  girls  are  Bubjeoted,  being  accelerated  by  habits  of 
luxury  and  indolence,  and  retarded  by  contrary  conditions.  On 
the  whole,  its  appearance  is  earlier  in  persons  dwelling  in  warm 

climes  than  in  those  inhabiting  colder  latitudes;  though  the 
extensive  investigations  of  Robertson  show  that  the  influence  of 
temperature  on  the  development  of  puberty  has  been  exaggerated. 
Much  of  the  influence  attributed  to  climate  appears  due  to  the 
custom  prevalent  in  many  hot  countries,  as  in  Hindostan,  of 
giving  girls  in  marriage  at  a  very  early  age,  and  inducing  sexual 
excitement  previous  to  the  proper  menstrual  time.  The  menstrual 
functions  continue  through  the  whole  fruitful  period  of  a  woman's 
life,  and  usually  cease  between  the  forty-fifth  and  fiftieth  years. 

The  several  menstrual  periods  usually  occur  at  intervals  of  a 
lunar  month,  the  duration  of  each  being  from  three  to  six  days. 
In  some  women  the  intervals  are  as  short  as  three  weeks  or 
even  less ;  while  in  others  they  are  longer  than  a  month.  The 
periodical  return  is  usually  attended  by  pain  in  the  loins,  a 
sense  of  fatigue  in  the  lower  limbs,  and  other  symptoms,  which  are 
different  in  different  individuals.  Menstruation  does  not  usually 
occur  in  pregnant  women,  or  in  those  who  are  suckling;  but  instances 
of  its  occurrence  in  both  these  conditions  are  by  no  means  rare. 

Corpus  Luteum. 

Immediately  before,  as  well  as  subsequent  to,  the  rupture  of  a 
Graafian  vesicle,  and  the  escape  of  its  ovum,  certain  changes  ensue 
in  the  interior  of  the  vesicle,  which  result  in  the  production  of  a 
yellowish  mass,  termed  a  Corpus  luteum,. 

When  fully  formed  the  corpus  luteum  of  mammiferous  animals 
is  a  roundish  solid  body,  of  a  yellowish  or  orange  colour,  and 
composed  of  a  number  of  lobules,  which  surround,  sometimes  a 
small  cavity,  but  more  frequently  a  small  stelliform  mass  of  white 
substance,  from  which  delicate  processes  pass  as  septa  between  the 
several  lobules.  Very  often,  in  the  cow  and  sheep,  there  is  n<> 
white  substance  in  the  centre  of  the  corpus  luteum ;  and  the 
lobules  projecting  from  the  opposite  walls  of  the  Graafian  vesicle 
appear  in  a  section  to  be  separated  by  the  thinnest  possible  lamina 
of  semi-transparent  tissue. 

"When  a  Graafian  vesicle  is  about  to  burst  and  expel  the  ovum, 
it  becomes  highly  vascular  and  opaque  ;  and,  immediately  before 


GENERATION  AND  DEVELOPMENT. 


[chap.  XX~ 


the  rupture  takes  place,  its  walls  appear  thickened  on  the  interior 
by  a  reddish  glutinous  or  fleshy-looking  substance.  Immediately 
after  the  rupture,  the  inner  layer  of  the  wall  of  the  vesicle  appears 


lI 


—    orpora  Uiti  .  Corpus  luteuni  of  about  the  sixth  "vvetk 

after  impregnation,  sho-wing  its  plicated  form  at  that  period,     i,  substance  of  the 

ova;-       z,    -    "  -■   noe  of  the  corpus  luteum ;  3,  a   greyish  coagulum  in  its  cavity. 

Paterson  rpua  tab  am  trsvo  clays  after  delivery:  d,  in  the  twelfth  week  after 

delivery.     \Montgo:_ 

pulpy  and  flocculent.  It  is  thrown  into  wrinkles  by  the  contrac- 
d  of  the  outer  layer,  and,  soon,  red  fleshy  mammillary  processes 
grow  from  it,  and  gradually  enlarge  till  they  nearly  fill  the  vesicle, 
and  even  protrude  from  the  orifice  in  the  external  covering  of  the 
ovary.  Subsequently  this  orifice  closes,  but  the  fleshy  growth 
within  still  increases  during  the  earlier  period  of  pregnancy,  the 
colour  of  the  substance  gradually  changing  from  red  to  yellow,  and 
its   :  insistence  becoming  firmer. 

The  corpus  luteum  of  the  human  female  (fig.  399)  differs  from 
that  of  the  domestic  quadruped  in  being  of  a  firmer  texture, 
and  having  more  frequently  a  \  srsistent  cavity  at  its  centre.  iaA 
in  the  stelliform  cicatrix,  which  remains  in  the  cases  where  the 
cavity  is  obliter  tl  _  proportionately  of  much  larger  bulk. 

The  quantity  of  yellow  subsf  formed  is  also  much  less  :  and, 

although  the  deposit  increases  after  the  vesicle  has  burst,  yet  it 
does  not  usually  form  mammillary  growths  projecting  int  I  ivity 
of  the  vesicle,  r  protrudes  from  the  orifice,  as  is  the 

in  other  Mammalia.      It  maintains  the  character  of  a  uniform,  or 
ly  uniform,   layer,  which  is   thrown  into  wrinkles,  in   conse- 
quence of  the  contraction   of  the   external   tunic   of  the   vesicle. 
After  the  orifice  of  the  vesicle  has  closed,  the  growth  of  the  yellow 
stance  continues  during  the  first   half  of  pregnancy,  till  the 
luced  t.  oiparatiyely  small  size,  or  is  obliterated  ; 


I  HAP.   XX.]  C0BFU8     LUTEUM.  yyj 

iii  the  latter  ease,  merely  a  white  Btelliform  cicatrix  remains  m  the 
n  ntrc  of  the  corpus  luteum. 

An  effusion  of  blood  generally  takes  place  into  the  cavity  <>f  the 
Graafian  vesicle  ;it  the  time  of  its  rapture,  especially  in  the  human 
subject,  but  it  has  no  >\\;\.rc  in  funning  the  yellow  body  ;  it  gradu- 
ally loses  its  colouring  matter,  and  acquires  the  character  of  a  mass 
of  fibrin.  The  serum  of  the  blood  sometimes  remains  included 
within  a  cavity  in  the  centre  of  the  coagulum,  and  then  the 
decolorised  fibrin  forms  a  membraniform  sac,  lining  the  corpus 
luteum.  At  other  times  the  serum  is  removed,  and  the  fibrin 
constitutes  a  solid  stelliform  mass. 

The  yellow  substance  of  which  the  corpus  luteum  consists,  both 
in  the  human  subject  and  in  the  domestic  animals,  is  a  growth 
from  the  inner  surface  of  the  Graafian  vesicle,  the  result  of  an 
increased  development  of  the  cells  forming  the  membrana  granu- 
losa, which  naturally  lines  the  internal  tunic  of  the  vesicle. 

The  first  changes  of  the  internal  coat  of  the  Graafian  vesicle 
in  the  process  of  formation  of  a  corpus  luteum,  seem  to  occur  in 
every  case  in  which  an  ovum  escapes ;  as  well  in  the  human 
subject  as  in  the  domestic  quadrupeds.  If  the  ovum  is  impreg- 
nated, the  growth  of  the  yellow  substance  continues  during 
nearly  the  whole  period  of  gestation  and  forms  the  large  corpus 
luteum  commonly  described  as  a  characteristic  mark  of  impreg- 
nation. If  the  ovum  is  not  impregnated,  the  growth  of  yellow 
substance  on  the  internal  surface  of  the  vesicle  proceeds,  in  the 
human  ovary,  no  further  than  the  formation  of  a  thin  layer, 
which  shortly  disappears ;  but  in  the  domestic  animals  it  con- 
tinues for  some  time  after  the  ovum  has  perished,  and  forms  a 
corpus  luteum  of  considerable  size.  The  fact  that  a  structure, 
in  its  essential  characters  similar  to,  though  smaller  than,  a 
corpus  luteum  observed  during  pregnancy,  is  formed  in  the 
human  subject,  independent  of  impregnation  or  of  sexual  union, 
coupled  with  the  varieties  in  size  of  corpora  lutea  formed  during 
pregnancy,  necessarily  renders  unsafe  all  evidence  of  previous 
impregnation  founded  on  the  existence  of  a  corpus  luteum  in 
the  ovary. 

The  following  table  by  Dalton,  expresses  well  the  differences 
between  the  corpus  luteum  of  the  pregnant  and  unimpregnated 
condition  respective! v. 


,  : 


j 


GENERATION  AND  DEVELOPMENT. 


[CHAP.   XX. 


Corpus  Luteum  of  MEN- 
STRUATION. 


CORPUS   Ll'TKUM   OF    PREG- 
NANCY. 


At  the  end  of   Three-quarters  of  an  inch  in  diameter  ;  central  clot  reddish  ; 


tl( 
i  '       month 


months. 


onths 


2V*  :  month* . 


convoluted  wall  | 
Smaller  ;        convoluted 
wall    bright    yellow  ; 
clot  still  red'    -    . 
Reduced   to  the   condi- 
tion of  an    insignifi- 
cant cicatrix. 
Absent. 


A:  -•.:.:. 


Larger ;  convoluted  wall  bright 
yellow  :  clot  still  reddish. 

Seven-eighths  of  an  inch  in  diame- 
ter ;  convoluted  wall  bright  yel- 
low ;  clot  perfectly  decolorised. 

Still  as  large  as  at  end  of  second 
nth;  clot  fibrinous;  convo- 
luted wall  paler. 

One-half  an  inch  in  diameter  ; 
central  clot  converted  into  a 
radiating  cicatrix  :  the  external 
wall  tolerably  thick  and  convo- 
luted, but  without  any  bright 
yellow  colour. 


'f2^^^^'- 


v 


F.r.  400. — fk  (urn     of    dog's    q 
The  rube  is  cut  in  "several  places,  both 

Ly  and  obliquely  ;  it  is  t 
to  be  lined  by  a  ciliated  epithelium, 
the  nuclei  of  which  are  well  shown. 
c,  connective  tissue.     (Schofield.) 


IMPREGNATION  OF  THE   OVUM. 
Male  Sexual  Functions. 

Testes. — The  fluid  of  the  male, 
by  which  the  ovum  is  impreg- 
nated, consists  essentially  of  the 
semen  secreted  by  the  testicles: 
and  to  this  are  added,  as  neces- 

y,  perhaps  to  its  perfection,  a 
material  secreted  by  the  vesiculce 
seminaleSj  as  well  as  the  secretion 
of  the  prostate  gland,  and  of 
'  ffper's  glands.  Portions  of 
these  several  fluids  are,  probably 
all  discharged,  together  with  the 
proper  secretion  of  the  testicles. 

The  secreting  structure  of  the 
testicle  and  its  duct  are  disposed 
of  in  two  contiguous  parts,  (i)  the 
body  of  the  testicle  enclosed 
within  a  tough  fibrous  membrane, 
the  tunica  albuginea,  on  the  outer 
surface  of  which    is   the    serous 


CHAP.  XX.] 


STRUCTURE  OF  TESTES. 


751 


covering  formed  by  the  tunica  vaginalis,  and  (2)  the  epididymis 

and  MM  <!'/<  r<  ns. 

Vas  Deferens. — The  vas  deferens,  or  duct  of  the  testicle,  which 
is  about  two  feet  in  length,  is  constructed  externally  of  connective 

tissue,  and  internally  is  lined  by  mucous  membrane,  covered  by 
columnar  epithelium  ;  while  between  these  two  coats  is  a  middle 
coat,  very  firm  and  tough,  made  up  chiefly  of  longitudinal  with 
some  circular  plain  muscu- 
lar fibres.  "When  followed 
back  to  its  origin,  the  vas 
deferens  is  found  to  pass  to 
the  lower  part  of  the  epidi- 
dymis, with  which  it  is  di- 
rectly continuous  (fig.  402), 
and  assumes  there  a  much 
smaller  diameter  with  an 
exceedingly  tortuous  course. 
The  epididymis,  which  is 
lined,  except  at  its  lowest 
part,  by  columnar  ciliated 
epithelium     (fig.    400),     is 


5b! 


wmss 


iffi 


?  ,»^ 


-  i P  sx^K  0  ri fi  ^«x\ ^ 


Fig.  401. — A  section  of  dog's  testicle,  highly  mag- 
nified, showing  three  "  tubuli  seminiferi," 
lined  and  largely  occupied  by  a  spheroidal 
epithelium,  the  numerous  nuclei  of  which  are 
well  seen ;  e,  connective  tissue  surrounding 
and  supporting  the  tubuli ;  sp,  masses  of 
spermatozoa  occupying  the  centre  of  tubuli  : 
the  small  black  bodies  scattered  about  are 
the  heads  of  the  spermatozoa.     (Schofield.) 


commonly  described  as  con- 
sisting (fig.  402)  of  a  globus 
minor  (g),  the  body  (e),  and 
the  globus  major  (I).  When 
unravelled,  it  is  found  to 
be  constructed  of  a  single 
tube,  measuring  about 
twenty  feet  in  length. 

At  the  globus  major  this  duct  divides  into  ten  or  twelve  small 
branches,  the  convolutions  of  which  form  coniform  masses,  named 
•coni  vasculosi ;  and  the  ducts  continued  from  these,  the  vasa 
efferent  ia,  after  anastomosing,  one  with  another  in  what  is  called 
the  rete  testis,  lead  finally  as  the  tubuli  recti  or  vasa  recta  to  the 
tubules  which  form  the  proper  substance  of  the  testicle,  wherein 
they  are  arranged  in  lobules,  closely  packed,  and  all  attached  to 
the  tough  fibrous  tissue  at  the  back  of  the  testicle.  The  epithe- 
lium of  the  coni  vasculosi  and  vasa  elferentia  is  columnar  and 
ciliated  ;  that  of  the  rete  testis  is  squamous. 


:i- 


GENERATION  AND  DEVELOPMENT. 


['HAP.   XX. 


-" 


Structure  of  Seminal  Tubes. — The  seminal  tubes,  or  tubuli 
seminiferi,  "which  compose  the  parenchyma  of  the  testicle,  are 
arranged  in  lobules  between  the  connective  tissue  septa. 

They  are  relatively  large,  very  wavy,  and  much  convoluted  ;  and 
they  possess   a  few  lateral  branches,  by  which  they  become  con- 
nected into   a   network.       They  form 
\\  terminal  loops,  and   in  the  peripheral 

portion  of  the  testis  the  tubules  are 
possessed  of  minute  lateral  csecal 
branchlets. 

Each  seminal  tubule  in  the  adult 
testis  is  limited  by  a  membrana  propria, 
which  appears  as  a  hyaline  elastic- 
membrane  containing  oval  flattened 
nuclei  at  regular  intervals.  Inside  this 
membrana  propria  are  several  layers  of 
epithelial  cells,  the  seminal  cells.  These 
consist  of  an  inner  and  outer  layer,  the 
latter  being  situated  next  the  mem- 
brana propria.  These  cells  are  of  two 
kinds,  those  that  are  in  a  resting  state 
and  those  that  are  in  a  state  of  divi- 
sion. The  latter  are  called  mother  cells, 
and  the  smaller  cells  resulting  from 
their  division  are  called  daughter  cells 
or  spermatoblasts.  From  these  the  sper- 
matozoa are  formed.  During  their  deve- 
lopment they  lie  in  groups,  but  when 
fully  formed  they  become  detached  and  fill  the  lumen  of  the 
seminiferous  tubule  (fig.  401). 


:. — I'1^  \of  I  • 

of  fk  .  -hoTrtng-  the  ar- 

rangement of  the  ducts.  The 
true  length  and  diameter  of  the 
ducts  have  been  disregarded. 
a,  a,  tubuli  seminif eri  coiled  up 
in  the  separate  lobes  :  b,  tu>  uli 
recti  or  vasa  recta  ;  r.  rete  testis: 
d,  vasa  efferentia  ending  in  the 
coni  vaseulosi :  .  - .  .  convo- 
luted canal  of  the  epidi  3 
h,  vas  deferen-  ;  \  -  :ion  of 
the  back  part  of  the  tunica 
albuginea :  i.  i,  fibrous  pro- 
cesses running  between  the 
lobes;  s,  mediastinum. 


Spermatozoa. — On  examining  the  spermatozoon  of  Triton  cristatus. 
one  of  the  Amphibia  which  possess  the  largest  of  all  Vertebrate  animals, 
Heneage  Gibbes  found  that  the  organism  (fig.  404)  consisted  of  (r/)  a  long 
pointed  head,  at  the  base  of  which  is  (Z/).  an  -      I  structure  joining  the 

head  to  (c),  a  long  filiform  hody  :  (<7),  a  fine  filament,  much  longer  than 
the  body,  is  connected  with  this  Matter  by  (e),  a  homogeneous  membrane. 

The  head,  as  it  appears  in  the  fresh  specimen,  has  a  different  refractive 
power  from  that  of  the  rest  of  the  organism,  and  with  a  high  power  appears 
to  be  a  light  green  colour  ;  there  is  also  a  central  iine  running  up  it.  from 
which  it  appears  to  be  hollow.  The  elliptical  structure  at  the  base  of  the 
head  connects  it  with  the  long  thre?.d-like  body,  and  the  filament  springs 


(HAL'.    XX.] 


SPERMATOZOA. 


753 


from  it.  "Whilst  the  spermatozoon  is  living,  this  filament  is  in  constant 
motion  ;  at  first  tin-  is  BO  quick  that  it  is  difficult  to  see  it.  but  as  its  vitality 
becomes  impaired  the  motion  gets  slower,  and  it  is  then  easily  perceived  to 
be  a  continuous  waving  from  side  to  side. 

In  Man  the  head  (fig.  405)  is  club-shaped,  and  from  its  base  springs  the 
very  delieate  filament  which  is  three  or  four  times  as  long  as  the  body  ;  and 
the  membrane  which  attaches  it  to  the  body 
is  much  broader,  and  allows  it  to  lie  at  a 
greater  distance  from  the  body  than  in  the 
Bpermatozoaof  any  other  Mammal  examined. 

( iibbes  concludes  : — 1st.  That  the  head  of 
the  spermatozoon  is  enclosed  in  a  sheath, 
which  is  a  continuation  of  the  membrane 
which  surrounds  the  filament  and  connects 
it  to  the  body,  acting  in  fact  the  part  of  a 
mesentery.  2ndly.  That  the  substance  of 
the  head  is  quite  distinct  in  its  composition 
from  the  elliptical  structure,  the  filament 
and  the  long  body,  and  that  it  is  readily 
acted  upon  by  alkalies  :  these  re-agents  have 
no  effect,  however,  on  the  other  part,  except- 
ing the  membranous  sheath.  31'dly.  That 
this  elliptical  structure  has  its  analogue  in 
the  Mammalian  spermatozoon  ;  in  the  one 
case  the  head  is  drawn  out  as  a  long  pointed 
process,  in  the  other  it  is  of  a  globular  form, 
and  surrounds  the  elliptical  structure.  4thly. 
That  the  motive  power  lies,  in  a  great  mea- 
sure, in  the  filament  and  the  membrane 
attaching  it  to  the  body. 


Fig.   405.  —  Spermatic    filaments 
from   the   human    vas   dt ' 

1,  magnified  350  diameters ;  2, 
magnified   800   diameter-  ; 
from  the  side  ;  b,  from  above. 
(From  Kulliker.) 


The  occurrence  of  spermatozoa  in  the  impregnating  fluid  of  nearly 
all  classes  of  animals  proves  that  they  are  essential  to  the  process 
of  impregation,  and  their  actual  contact  with  the  ovum  is  neces- 
sary for  its  development ;  but  concerning  the  manner  of  their 
action  nothing  is  known. 

The  seminal  fluid  is,  probably,  after  the  period  of  puberty, 
secreted  constantly,  though,  except  under  excitement,  very  slowly, 
in  the  tubules  of  the  testicles.  From  these,  it  passes  along  the 
vasa  deferentia  into  the  vesicuhe  seminales,  whence,  if  not  ex- 
pelled in  emission,  it  may  be  discharged,  as  slowly  as  it  enters 
them,  either  with  the  urine,  which  may  remove  minute  cruantities- 
mingled  with  the  mucus  of  the  bladder  and  the  secretion  of  the 
prostate,  or  from  the  urethra  in  the  act  of  defecation. 

Vesiculae  Seminales — The  vesicuke  seminales  (fig.  406)  have 
the  appearance  of  outgrowths  from  the  vasa  deferentia.  Each 
vas  deferens,  just  before  it  enters  the  prostate  gland,  through  part 

3  c 


754 


GENERATION  AND  DEVELOPMENT. 


[CHA1\   XX. 


of  which  it  passes  to  terminate  in  the  urethra,  gives  off  a  side- 
branch,  which  bends  back  from  it  at  an  acute  angle  :   and  this 

branch  dilating,  vari- 
ously branching,  and 
pursuing  in  both  it- 
self and  its  branches 
a  tortuous  course, 
forms  the  vesicula 
seminalis. 

Structure. — Each 
of  the  vesicular,  there- 
fore, might  be  unra- 
velled into  a  single 
branching  tube,  sac- 
culated, convoluted, 
and  folded  up.  The 
structure  of  the  vesi- 
cular resembles  close- 
ly that  of  the  vasa 
deferentia.  The  mu- 
cous membrane  lining 
the  vesicular  semi- 
nales,  like  that  of  the 
gall  -  bladder,  is  mi- 
nutely wrinkled  and 
set  with  folds  and 
ridges  arranged  so  as 
to  give  it  a  finely 
reticulated  appear- 
ance. 

Functions.  —  To 
the  vesicular  semi- 
nales  a  double  func- 
tion may  be  assigned ; 
for  they  both  secrete 
some  fluid  to  be  added 
to  that  of  the  testi- 
cles, and  serve  as  reservoirs  for  the  seminal  fluid.  The  former 
is   their   most    constant    and   probably   most   important    office ; 


Fig.  4°4- 


Fig.  405. 


Fig.  404. — Spermatozoon    of  Salamandra    Maculata.     Fresh 

mounted  in  glycerin.      X  950,  reduced  one  half. 
Fig.  405. — Human  spermatozoa.     X  2500.     (H.  Gibbes.) 


'II  \l\    XX.  ] 


YKSKTI..K    SKMIN  \l  ES. 


755 


for  in  tlir  horse,  bear,  guinea-pig,  and  several  other  animals,  in 
whom  the  vesioulee  seminales  are  large  and  of  apparently  active 
function,  they  do  not  communicate  with  the  vasa  deferentia,  but 
pour  their  secretions,  separately,  though  it  may  be  simultaneously, 


Fig.  406. — Dissection  of  (he  hose  of  thr  bladder  and  prostate  gland,  showing  the  vesicula 

v  and  vasa  deft  n  ntia.  a,  lower  surface  of  the  bladder  at  the  place  of  reflexion  of 
the  peritoneum ;  b,  the  part  above  covered  by  the  peritoneum ;  i,  left  vas  deferens, 
ending  in  e,  the  ejaculatory  duct ;  the  vas  deferens  has  been  divided  near  <,  and  all 
except  the  vesicle  portion  has  been  taken  away ;  a,  left  vesicula  seminalis  joining 
the  same  duct ;  s,  s,  the  riirht  vas  deferens  and  right  vesicula  seminalis,  which  has 
been  unravelled  ;  />,  under  side  of  the  prostate  gland  ;  m,  part  of  the.  urethra  ;  u,  », 
the  ureters  (cut  short),  the  right  one  turned  aside.     (Haller.) 


into  the  urethra.  In  man,  also,  when  one  testicle  is  lost,  the 
corresponding  vesicula  seminalis  suffers  no  atrophy,  though  its 
function  as  a  reservoir  is  abrogated.  But  how  the  vesiculre 
seminales  act  as  secreting  organs  is  unknown ;  the  peculiar 
brownish  fluid  which  they  contain  after  death  does  not  properly 
represent  their  secretion,  for  it  is  different  in  appearance  from 
anything  discharged  during  life,  and  is  mixed  with  semen.  It 
is  nearly  certain,  however,  that  their  secretion  contributes  to  the 
proper  composition  of  the  impregnating  fluid  ;  for  in  all  the 
animals  in  whom  they  exist,  and  in  whom  the  generative  func- 
tions are  exercised  at  only  one  season  of  the  year,  the  vesiculae 
seminales,  whether  they  communicate  with  the  vasa  deferentia  or 

3  c  2 


756  GENERATION    AND    DEVELOPMENT.  [chap.  xx. 

not,  enlarge  commensurately  "with  the  testicles  at  the  approach  of 
that  season. 

That  the  vesicula3  are  also  reservoirs  in  which  the  seminal  fluid 
may  lie  for  a  time  previous  to  its  discharge,  is  shown  by  their 
commonly  containing  the  seminal  filaments  in  larger  abundance 
than  any  portion  of  the  seminal  ducts  themselves  do.  The  fluid- 
like mucus,  also,  which  is  often  discharged  from  the  vesiculse  in 
straining:  during  defalcation,  commonly  contains  seminal  filaments. 
But  no  reason  can  be  given  why  this  office  of  the  vesicular  should 
not  be  equally  necessary  to  all  the  animals  whose  testicles  are 
organised  like  those  of  man,  or  why  in  many  animals  the  vesicuke 
are  wholly  absent. 

There  is  an  equally  complete  want  of  information  respecting 
the  secretions  of  the  prostate  and  Cowper's  glands,  their  nature 
and  purposes.  That  they  contribute  to  the  right  composition  of 
the  impregnating  fluid,  is  shown  both  by  the  position  of  the 
glands  and  by  their  enlarging  with  the  testicles  at  the  approach 
of  an  animal's  breeding  time.  But  that  they  contribute  only  a 
subordinate  part  is  shown  by  the  fact,  that,  when  the  testicles  are 
lost,  though  these  other  organs  be  perfect,  all  procreative  power 
ceases. 

The  Semen. 

The  mingled  secretions  of  all  the  organs  just  described,  form  the 
semen,  which  is  a  thick  whitish  fluid  composed  of  a  liquor  seminis 
and  spermatozoa,  with  detached  epithelial  cells.  The  fluid  part  has 
not  been  satisfactorily  analysed  :  but  Henle  says  it  contains  fibrin, 
because  shortly  after  being  discharged,  flocculi  form  in  it  by 
spontaneous  coagulation,  and  leave  the  rest  of  it  thinner  and  more 
liquid,  so  that  the  filaments  move  in  it  more  actively. 

Nothing  has  shown  what  it  is  that  makes  this  fluid  with  its 
corpuscles  capable  of  impregnating  the  ovum,  or  (what  is  yet 
more  remarkable)  of  giving  to  the  developing  offspring  all  the 
characters,  in  features,  size,  mental  disposition,  and  liability  to 
disease,  which  belong  to  the  father.  This  is  a  fact  wholly  inex- 
plicable :  and  is,  perhaps,  only  exceeded  in  strangeness  by  those 
facts  which  show  that  the  seminal  fluid  may  exert  such  an  influ- 
ence, not  only  on  the  ovum  which  it  impregnates,  but,  through 
the  medium  of  the  mother,  on  many  which  are  subsequently  im- 
pregnated by  the  seminal  fluid  of  another  male. 


ohap.  xx.]  CHANGES   IX  THE   OVUM.  757 

It  has  been  of  ten  observed  thai  a  well-bred  bitch,  if  Bhe  have  been  once 
impregnated  by  a  mongrel  dog,  will  do1  bear  thorough-bred  puppies  in  the 
next  two  01  three  Litters  after  that  succeeding  the  copulation  with  the 

tnongrel.  But  the  best  instance  of  the  kind  was  in  the  case  of  a  mare 
belonging  to  Lord  Morten,  who,  while  he  was  in  India,  wished  to  obtain  a 
cross-breed  between  the  horse  and  the  quagga,  and  caused  this  mare  to  be 
covered  by  a  male  quagga.  The  foal  thai  she  next  bore  had  the  distinct 
marks  of  the  quagga,  in  the  shape  of  its  head,  black  bars  on  the  legs  and 
shoulders,  and  other  characters.  After  this  time  she  was  thrice  covered  by 
horses,  and  every  time  the  foal  she  bore  had  still  distinct,  though  decreasing, 
marks  of  the  quagga  ;  the  peculiar  characters  of  the  quagga  being  thus 
impressed  not  only  on  the  ovum  then  impregnated,  but  on  the  three  follow- 
ing "va  impregnated  by  horses.  It  would  appear,  therefore,  that  thy  con- 
stitution of  an  impregnated  female  may  become  so  altered  and  tainted  with 
the  peculiarities  of  the  impregnating  male,  through  the  medium  of  the 
foetus,  that  she  necessarily  imparts  such  peculiarities  to  any  offspring  she 
may  subsequently  bear  by  other  males.  Of  the  direct  means  by  which  a 
peculiarity  of  structure  on  the  part  of  a  male  is  thus  transmitted,  nothing 
whatever  is  known. 

As  bearing  upon  this  subject,  the  following  note  kindly  given  to  the  Editors 
by  Mr.  S.  Probart  may  be  added  : — On  the  Farm  "Wellwood,  the  property  of 

Charles  R ,  Esq.,  in  the  Division  of  Graaff  Re  met,  Cape  of  Good  Hope. 

there  is  at  present  running  an  aged  mare  with  a  numerous  progeny.  Some 
years  ago  she  foaled  for  three  successive  seasons  to  a  donkey  ;  after  that  she 
gave  birth  to  a  mare  foal,  to  a  horse.  This  filly  was  a  chestnut,  and  did 
not  exhibit  any  taint  of  the  donkey  by  which  her  dam  had  previously  foaled. 
But  when  she  in  her  turn  foaled  to  a  horse,  hir  young  bore  the  distinct 
marks  along  the  back  and  withers,  and  rings  round  the  lower  parts  of  the 
legs,  which  are  the  peculiarity  of  the  ass  and  the  mule.  Three  foals  she  has 
had  are  all  so  marked. 


Development. 

Changes  in  the  Ovum  up  to  formation  of  the  Blastoderm. 

The  earlier  stages  in  development  are  so  fundamentally  similar 
in  all  vertebrate  animals,  from  Fishes  up  to  Man,  that  the  gaps 
existing  in  our  knowledge  of  the  process  in  the  higher  Mammalia, 
such  as  man,  may  be  in  part,  at  any  rate,  filled  up  by  the  more 
accurate  knowledge  which  we  possess  of  the  development  of  the 
ovum  in  such  animals  as  the  trout,  frog,  and  fowl. 

One  important  distinction  between  the  ova  of  various  Vertebrata  should  be 
remembered.  In  the  hen's  egg,  besides  the  shell  and  the  white  or  albumen, 
two  other  structures  are  to  be  distinguished — the  germ,  often  called  the  cica- 
tricula  or  '"tread,''  and  the  yelk  enclosed  in  its  vitelline  membrane. 

The  germ  is  essentially  a  cell,  consisting  of  protoplasm  enclosing  a  nucleus 
and  nucleolus.  It  alone  participates  in  the  process  of  segmentation  (to  be 
immediately  described),  the  great  mass  of  the  yelk  (food-yelk)  remaining 


758  GENERATION    AND    DEVELOPMENT.  [chap.  xx. 

quite  unaffected  by  it.  Since  only  the  germ,  which  forms  but  a  small  por- 
tion of  the  yelk,  undergoes  segmentation,  the  ovum  is  called  meroblartie* 

In  the  Mammalia,  on  the  other  hand,  there  is  no  large  unsegmented  mass 
corresponding  to  the  food-yelk  of  birds  :  the  entire  ovum  undergoes  segmen- 
tation, and  is  hence  termed  holoilastic. 

The  eggs  of  Fishes,  Reptiles,  and  Birds,  are  meroblastic,  while  those  of 
Amphibia  and  Mammalia  are  holoblastic. 

Of  the  changes  which  the  mammalian  ovum  undergoes  previous 
to  the  formation  of  the  embryo,  some  occur  while  it  is  still  in 
the  ovary,  and  are  apparently  independent  of  impregnation  : 
others  take  place  after  it  has  reached  the  Fallopian  tube.  The 
knowledge  we  possess  of  these  changes  is  derived  almost  exclu- 
sively from  observations  on  the  ova  of  the  bitch  and  rabbit :  but 
it  may  be  inferred  that  analogous  changes  ensue  in  the  human 
ovum. 

Bischoff  describes  the  yelk  of  an  ovarian  ovum  soon  after  coitus 
as  being  unchanged  in  its  characters,  with  the  single  exception  of 
being  fuller  and  more  dense ;  it  is  still  granular,  as  before,  and 
does  not  possess  any  of  the  cells  subsequently  found  in  it.  The 
terminal  vesicle  always  disappears,  sometimes  before  the  ovum 
leaves  the  ovary,  at  other  times  not  until  it  has  entered  the  Fallo- 
pian tube  ;  but  always  before  the  commencement  of  the  metamor- 
phosis of  the  yelk. 

As  the  ovum  approaches  the  middle  of  the  Fallopian  tube,  it 
beo-ins  to  receive  a  new  investment,  consisting  of  a  layer  of  trans- 
parent  albuminous  or  glutinous  substance,  which  forms  upon  the 
exterior  of  the  zona  pellucida.  It  is  at  first  exceedingly  fine,  and, 
owing  to  this,  and  to  its  transparency,  is  not  easily  recognised  : 
but  at  the  lower  part  of  the  Fallopian  tube  it  acquires  considerable 
thickness. 

Segmentation. — The  first  visible  result  of  fertilisation  is  a 
slight  amoeboid  movement  in  the  protoplasm  of  the  ovum :  this 
has  been  observed  in  some  fish,  in  the  frog,  and  in  some  mammals. 
Immediately  succeeding  to  this  the  process  of  segmentation  com- 
mences, and  is  completed  during  the  passage  of  the  ovum  through 
the  Fallopian  tube.  The  yelk  becomes  constricted  in  the  middle, 
and  surrounded  by  a  furrow  which  gradually  deepening,  at 
length  cuts  the  yelk  in  half,  while  the  same  process  begins  almost 
immediately  in  each  half  of  the  yelk,  and  cuts  it  also  in  two.  The 
same  process  is  repeated  in  each  of  the  quarters,  and  so  on,  until 


OHAP.  XX.] 


SEGMENT  ATI  i  )\. 


759 


at  last  by  continual  cleavings,  the  whole  yelk  is  changed  into  a 
mulberry -like-mass  of  small  and  more  or  less  rounded  bodies, 
sometimes  called  "vitelline  spheres,"  the  whole  still  enclosed  by 
the  zona  pettucida  or  vitelline  membrane  (tig.  406*).  Each  of  these 
little  spherules  contains  a  transparent 
vesicle,  like  an  oil-globule,  which  is  seen 
with  difficulty,  on  account  of  its  being 
enveloped  by  the  yelk-granules  which 
adhere  closely  to  its  surface. 

The  cause  of  this  singular  subdivision 
of  the  yelk  is  quite  obscure  :  though  the 
immediate  agent  in  its  productions  seems 
to  be  the  central  vesicle  contained  in 
each  division  of  the  yelk.  Originally 
there  "was  probably  but  one  vesicle,  situ- 
ated in  the  centre  of  the  entire  granular 
mass  of  the  yelk,  and  probably  derived 
from  the  germinal  vesicle.  This  divides 
and  subdivides  :  each  successive  division 
and  subdivision  of  the  vesicle  being 
accompanied  by  a  corresponding  division 
of  the  yelk. 

About  the  time  at  which  the  Mamma- 
lian ovum  reaches  the  uterus,  the  process 
of  division  and  subdivision  of  the  yelk 
appears  to  have  ceased,  its  substance 
having  been  resolved  into  its  ultimate 
and  smallest  divisions,  while  its  surface 
presents  a  uniform  finely-granular-aspect, 
instead  of  its  late  mulberry-like  appear- 
ance. The  ovum,  indeed,  appears  at 
tirst  sight  to  have  lost  all  trace  of  the 

cleaving  process,  and,  with  the  exception  of  being  paler  and  more 
translucent,  almost  exactly  resembles  the  ovarian  ovum,  its  yelk 
consisting  apparently  of  a  confused  mass  of  finely  granular 
substance.  But  on  a  more  careful  examination,  it  is  found  that 
these  granules  are  aggregated  into  numerous  minute  spheroidal 
masses,  each  of  which  contains  a  clear  vesicle  or  nucleus  in  its 
centre,  and  is,  in  fact,  an  "  embryonal  cell."     The  zona  pellucida, 


Fig.  406*.  —  Diagrams  of  the 
various  stages  of  cleavage  of 
(he  yetJc  (Dalton). 


yCo  GENERATION   AND    DEVELOPMENT.  [chap.  xx. 

and  the  layer  of  albuminous  matter  surrounding  it,  have  at  this 
time  the  same  character  as  when  at  the  lower  part  of  the  Fal- 
lopian tube. 

The  passage  of  the  ovum,  from  the  ovary  to  the  uterus,  occupies 
probably  eight  or  ten  days  in  the  human  female. 

When  the  peripheral  cells,  which  are  formed  first,  are  fully 
developed,  they  arrange  themselves  at  the  surface  of  the  yelk  into 
a  kind  of  membrane,  and  at  the  same  time  assume  a  polyhedral 
shape  from  mutual  pressure,  so  as  to  resemble  pavement  epithe- 
lium. The  deeper  cells  of  the  interior  pass  gradually  to  the 
surface  and  accumulate  there,  thus  increasing  the  thickness  of 
the  membrane  already  formed  by  the  more  superficial  layer  of 
cells,  while  the  central  part  of  the  yelk  remains  filled  only  with  a 
clear  fluid.  By  this  means  the  yelk  is  shortly  converted  into  a 
kind  of  secondaiy  vesicle,  the  walls  of  which  are  composed  exter- 
nally of  the  original  vitelline  membrane,  and  within  by  the  newly 
formed  cellular  layer,  the  blastodermic  or  germinal  membrane,  as 
it  is  called. 

Layers  of  the  Blastoderm. — Before  long  the  blastoderm  is 
found  to  consist  of  three  fundamental  layers,  Epiblast,  Jlesoblast, 
and  Hypoblast. 

The  way  in  which  these  are  formed  may  be  readily  studied  in 
a  hen's  egg.     In  a  freshly  laid  hen's  egg,  before  incubation  has 


^^^M^m^o 


zXSGCO 


m 

c 


D 


fS^s 


Fig.  407. — Vertical  section  of  area  peUueida,  and  area  opaca  (left  extremity  of  figure)  of 
blastoderm  of  a  fresh-laid  egg  (uninoubated) .  8,  superficial  layer  corresponding  to 
epiblast ;  D,  deeper  layer,  corresponding  to  hypoblast,  and  probably  in  part  to  meso- 
blast ;  M,  large  "  formative  cells,"  filled  -with  yelk  granules,  and  lying  on  the  floor  of 
the  segmentation  cavity  ;  A,  the  white  yelk  immediately  underlying  the  segmenta- 
tion cavity  (Strieker). 

commenced,  the  blastoderm  is  found  to  consist  of  two  layers,  fig. 
407,  S  and  D),  the  upper  of  which  forms  a  distinct  membrane  of 
columnar  cells,  while  the  lower  stratum  consists  of  larger  cells 
irregularly  arranged. 


chap,  xx.]  RUDIMENTS  <>F  THE  EMBRYO.  y6l 

Beneath  the  blastoderm  there  are  a  few  scattered  larger  cells — 
"formative  cells.*'  In  the  lower  of  the  above  two  layers,  some 
cells  become  flattened  and  unite  to  form  a  distinct  membrane 
(hypoblast);  the  remaining  cells  of  the  lower  layer,  together  with 
some  of  the    large  formative   cells,   which  migrate  by  amoeboid 


*^sm!b 


^,§fc 


Fig.  408. — Vertical  section  of  Llrrsfnd<-rm  of  chick  (ist  day  of  incubation).  S,  epiblast,  con- 
sisting of  short  columnar  cells  ;  I>,  hypoblast,  consisting  of  a  single  layer  of  flattened 
cells ;  -1/,  "  formative  cells."  They  are  seen  on  the  right  of  the  figure,  passing  in 
between  the  epiblast  and  hypoblast  to  form  the  mesoblast  ;  A .  white  yelk  granules. 
Many  of  the  large  "  formative  cells"  are  seen  containing  these  granules  (Strieker). 

movement  round  the  edge  of  the  hypoblast  (fig.  408  J/, ),  consti- 
tute a  third  layer  (mesoblast). 

These  important  changes  are  among  the  earliest  results  of 
incubation. 

From  the  epiblast  are  ultimately  developed  the  epidermis  and  its  various 
appendages,  also  the  cerebrospinal  nerve  centres,  the  sensorial  epithelium  of 
the  organs  of  special  sense  (eye.  ear,  nose),  and  the  epithelium  of  the  mouth 
and  salivary  glands. 

From  the  Ju/pohla.sf  is  developed  the  epithelium  of  the  whole  digestive 
canal  together  with  that  lining  the  ducts  of  all  the  glands  which  open  into 
it  :  also  the  glandular  parenchyma  of  the  glands  (e.g..  liver  and  pancreas) 
connected  with  it,  and  the  epithelium  of  the  respiratory  track. 

From  the  mesoblast  are  derived  all  the  tissues  and  organs  of  the  body 
intervening  between  these  two,  the  whole  group  of  the  connective  tissues, 
the  muscles  and  the  cerebro-spmal  and  sympathetic  nerves,  with  the  vascular 
and  genito-urinary  systems,  and  all  the  digestive  canal  with  its  various 
appendages  with  the  exception  of  the  lining  epithelium  above  mentioned. 


First  rudiments  of  the  Embryo  and  its  chief  organs. 

Germinal  area. — The  position  in  which  the  embryo  is  about 
to  appear  is  early  marked  out  by  a  central  roundish  opacity  in 
the  blastoderm,  due  to  the  accumulation  of  cells  in  this  region. 
This  germinal  area,  which  is  at  first  circular,  changes  its  shape 
becoming  pyriform,  and  finally  an  elongated  oval  constricted  in 
the  middle  like  a  savoy  biscuit. 


~62 


GENERATION    AXI)    DEVELOPMENT. 


[chap.  XX. 


The  central  portion  becomes  transparent,  and  thus  we  have  an 
area  pellueida,  surrounded  by  an  area  opaca  (fig.  409). 

Primitive  Groove. — The  first 
trace  of  the  embryo  is  a  shallow 
longitudinal  groove  (primitive 
groove),  which  appears  towards  the 
posterior  part  of  the  area  pellueida 
(figs.  409,  412). 

MedullaryGrccve. — The  pri- 
mitive groove  is  but  transitory, 
and  is  soon  displaced  by  the  medul- 
lary groove,  which  first  appears  at 
the  anterior  extremity  of  the  future 
embryo,  and  grows  backwards  gra- 
dually causing  the  disappearance 
of  the  primitive  groove. 

Laminae  dorsales. —  The    me- 
dullary canal  is  bounded  by  two  longitudinal  elevations  (laminct 
-  '  les)  which  are  folds  consisting  entirely  of  cells  of  the  epiblast  : 


Fig.  409. — Impregnated  egg,  tcith  com- 
wumetmait  of  formation  of  embryo; 
showing  the  area  germinativa  or 
embryonic  spot,  the  area  pellueida, 
and  the  primitive  srroove  or  trace 
Dalton  . 


Fig.  410. — Trammt  -  -  turn  through  embryo  rind:  {26  hrs.).  <7,  epiblast  ;  b,  mesoblast ;  c, 
hypoblast  ;  >l,  central  portion  of  mesoblast,  -which  is  here  fused  with  epiblast ;  e,  pri- 
mitive groove  ;  /",  dorsal  ridge    Klein  . 


these  grow  up  and  arch  over  the  medullary  groove  (fig.  411)  till 
they  coalesce  in  the  middle  line,  converting  it  from  an  open 
furrow  into  a  closed  tube — the  primitive  cerebrospinal  axis. 
Over  this  closed  tube,  the  walls  of  which  consist  of  more  or  less 
cylindrical  cells,  the  superficial  layer  of  the  epiblast  is  now 
continued  as  a  distinct  membrane. 


CHAP.   XX. 


LAMIK2E   DORSALES. 


76; 


The  union  of  the  medullary  folds  or  laminae  dorsales  takes  place  first  about 
the  ueck  of  the  future  embryo  ;  they  soon  after  unite  over  the  region  of  the 
head,  while  the  closing  in  of  the  groove  progresses  much  more  slowly  to- 


///    <u 


Fig.  411. — Diagram  0/ transverse  section  through  an  embryo  be/ore  the  tilosing-inof  the  medullary 
groove,  m,  cells  of  epiblast  lining  the  medullary  groove -which  will  form  the  spinul 
cord  ;  h,  epiblast ;  d,  hypoblast ;  ch,  noto-chord ;  u,  proto vertebra ;  sp,  mesoblast ;  w, 
edge  of  lamina  dorsalis",  folding  over  medullary  groove  (KOlliker). 


wards  the  hinder  extremity  of  the  embryo.  The  medullary  groove  is  by  no 
means  of  uniform  diameter  throughout,  but  even  before  the  dorsal  laminae 
have  united  over  it,  is  seen  to  be  dilated  at  the  anterior  extremity  and 
obscurely  divided  by  constrictions  into  the  three  primary  vesicles  of  the 
brain. 


Fig.  412  —Portion  of  the  germinal  membrane,  with  rudiments  of  the  embryo  ;  trom  the  ovum  of  a 
bitch.  The  primitive  groove,  a.  is  not  vet  closed,  and  at  its  upper  or  cephalic  end  pre- 
sents three  dilatations,  b,  which  correspond  to  the  three  divisions  or  vesicles  of  the 
brain.  At  its  lower  extremitv  the  groove  presents  a  lancet-shaped  dilatation  (sinus 
rhomboidalis)  c.  The  margins  of  the  groove  consist  of  clear  pellucid  nerve-substance. 
Along  the  bottom  of  the  groove  is  observed  a  faint  streak,  which  is  probably  the  chorda 
dorsalis.     i>.  Vertebral  plates  (Bischoff  ) . 

The  part  from  which  the  'spinal  cord  is  formed  is  of  nearly  uniform 
calibre,  while  towards  the  posterior  extremity  is  a  lozeuge-shaped  dilatation, 
which  is  the  last  part  to  close  in  (fig.  412). 


;64 


GENERATION    AND    DEVELOPMENT. 


[chap.  XX 


Notochord. — At  the  same  time  there  appears  in  the  middle 
line,  immediately  beneath    the  floor  of  the  medullary  groove,   a 

rod-shaped  structure  formed  by  an 
aggregation  of  cells  of  the  meso- 
blast ;  it  soon  becomes  quite  distinct 
from  the  remainder  of  the  mesoblast, 
and  constitutes  an  axial  cord  (noto- 
chord, chorda  dorsalis)  (ch,  fig.  414) 
which  extends  nearly  the  whole 
length  of  the  medullary  canal,  ter- 
minating anteriorly  beneath  the 
middle  one  of  the  three  cerebral 
vesicles,  and  occupies  the  future 
position  of  the  bodies  of  the  vertebra) 
and  basis  cranii. 

Proto  vertebrae. —Simultaneously 
on  each  side  of  the  notochord  ap- 
pears a  longitudinal  thickening  of 
the  mesoblast. 

Thus  we  have  two  lateral  plates 
which  when  viewed  from  above  are 
seen  to  be  divided  into  a  number  of 
squarish  segments  {protovertehxe)  by 
the  formation  of  transverse  clefts. 
The  first  three  or  four  of  these  pro- 
tovertebrce  make  their  appearance 
in  the  cervical  region,  while  one  or 
two  more  are  formed  in  front  of  this 
point :  and  the  series  is  continued 
backward  till  the  whole  medullary 
canal  is  flanked  by  them  (fig.  413). 

Splitting  of  the  Mesoblast.  — 
External  to  the  protovertebrse,  the 
mesoblast  now  splits  into  two  lamina3 
{parietal  and  visceral) :  of  these  the 
former,  when  traced  out  from  the 
central  axis,  is  seen  to  be  in  close 
apposition  with  the  epiblast  and 
gives  origin  to  the   parietes  of  the 


Fig-.  413. — Embryo  chick  (,36  hours), 
viewed  from  beneath  as  a  transparent 
object  (magnified),  pi,  outline  of 
pellucid  area  ;  FB,  fore-brain,  or 
first  cerebral  vesicle  :  from  its  sides 
project  op,  the  optic  vesicles ;  SO, 
backward  limit  of  somatopleure 
fold,  "tucked  in"  under  head; 
a,  headfold  of  true  amnion  ;  a',  i~e- 
fiected  layer  of  amnion,  sometimes 
termed  "  false  amnion  ;  "  sp,  back- 
ward limit  of  splanchnopleure  folds, 
along  which  run  the  omphalomesa- 
raic  veins  uniting  to  form  h,  the 
heart,  which  is  continued  forwards 
into  ba,  the  bulbus  arteriosus  ;  d,  the 
fore-gut,  lying  behind  the  heart, 
and  having  a  wide  crescentic  open- 
ing between  the  splanchnopleure 
folds ;  HB,  hind-brain ;  JIB,  mid- 
brain; pv,  proto  vertebrae  lying  be- 
hind the  fore-gut ;  mc,  line  of  junc- 
tion of  medullary  folds  and  of 
notochord  ;  ch,  front  end  of  noto- 
chord ;  vpl,  vertebral  plates  ;  pr, 
the  primitive  groove  at  its  caudal 
end  (Foster  and  Balfour) . 


CUM1.    XX. J 


SPLITTING    <»F   THE   MESOBLAST. 


70S 


trunk,  while  the  latter  adheres  more  or  less  closely  to  the  hypo- 
blast, and  gives  rise  to  the  serous  and  muscular  walls  of  the 
alimentary  canal  and  several  other  parts  (fig.  414). 


Mr 


JP? 


So 


Fig.  414. — Transverse  section  through  dorsal  region  of  embryo  chick  (45  hrs.).  One  half  of  the 
section  is  represented  :  if  completed  it  would  extend  as  far  to  the  left  as  to  the  right  of 
the  line  of  the  medullary  canal  {Me).  A,  epiblast;  0,  hypoblast,  consisting  of  a 
single  layer  of  flattened  cells  ;  Me,  medullary  canal ;  Pc,  proto vertebra  ;  Wd,  "Wolffian 
duct ;  So,  somatopleure ;  £/>,  splanchnopleure  ;  pj>,  pleuro-peritoneal  cavity  ;  eh,  noto- 
chord  :  ao,  dorsal  aorta,  containing  blood  cells ;  v,  blood-vessels  of  the  yolk-sac  (Foster 
and  Balfour  . 

The  united  parietal  layer  of  the  mesoblast  with  the  epiblast  is 
termed  Somatopleure,  the  united  visceral  layer  and  hypoblast, 
Splanchnopleure.  The  space  between  them  is  the  pleuro-peritoneal 
cavity,  which  becomes  subdivided  by  subsequent  partitions  into 
pericardium,  pleura,  and  peritoneum. 

Head  and  Tail  Folds.  Body  Cavity. — Every  vertebrate 
animal  consists  essentially  of  a  longitudinal  axis  (vertebral  column) 
with  a  neural  canal  above  it,  and  a  body-cavity  (containing  the 
alimentary  canal)  beneath. 

We  have  seen  how  the  earliest  rudiments  of  the  central  axis 
and  the  neural  canal  are  formed ;  we  must  now  consider  how 
the  general  body-cavity  is  developed.  In  the  earliest  stages  the 
embryo  lies  flat  on  the  surface  of  the  yelk,  and  is  not  clearly 
marked  off  from  the  rest  of  the  blastoderm  :  but  gradually  a 
crescentic  depression  (with  its  concavity  backwards)  is  formed  in 
the  blastoderm,  limiting  the  head  of  the  embryo  ;  the  blastoderm 
is,  as  it  were,  tucked  in  under  the  head,  which  thus  comes  to 
project  above  the  general  surface  of  the  membrane  :  a  similar 
tucking  in  of  blastoderm  takes  place  at  the  caudal  extremity, 
and  thus  the  head  and  tail  folds  are  formed  (fig.  415). 

Similar  depressions  mark  off  the  embryo  laterally,  until  it  is 


766 


GENERATION  AND  DEVELOPMENT. 


[chap.  XX. 


completely  surrounded  by  a  sort  of  moat  which  it  overhangs  on 
all  sides,  and  which  clearly  defines  it  from  the  yelk. 


N.C 


\ 


Sp  pfi 


Fig.  41=;. — Diagrammatic  longitudinal  section  through  the  axis  of  an  embryo.  The  head-fold 
has  commenced,  but  the  tail-fold  has  not  yet  appeared.  FSo,  fold  of  the  somato- 
pleure  ;  FSp,  fold  of  the  splanchnopleure  ;  the  line  of  reference,  FSo,  lies  outside  the 
embryo  in  the  "  moat,"  which  marks  off  the  overhanging  head  from  the  amnion  ;  D, 
inside  the  embryo,  is  that  part  which  is  to  become  the  fore-gut ;  FSo  and  FSp,  are  both 
parts  of  the  head-fold,  and  travel  to  the  left  of  the  figure  as  development  proceeds  ; 
p-p,  space  between  somatopleure  and  splanehnopleiire,  pleuro-peritoneal  cavity ;  Am, 
commencing  head-fold  of  amnion;  JVC,  neural  canal;  Ch.  notochord  ;  Ht,  heart  ;  A, 
B,  G,  epiblast,  mesoblast,  hypoblast  (Foster  and  Balfour). 


'nrw^ 


.  416. — Diagrammatic  section  showing  the  relation  in  o  mammal  between  the  primitive  alimen- 
tary canal  and  the  membranes  of  the  ovum.  The  stage  represented  in  this  diagram  cor- 
responds to  that  of  the  fifteenth  or  seventeenth  day  in  the  human  embryo,  previous  to 
the  expansion  of  the  allantois  :  c,  the  villous  chorion  ;  a,  the  amnion ;  a',  the  place  of 
convergence  of  the  amnion  and  reflexion  of  the  false  amnion  a"  a",  or  outer  or  corneous 
layer ;  e,  the  head  and  trunk  of  the  embryo,  comprising  the  primitive  vertebrae  and 
cerebro-spinal  axis  ;  i,  i,  the  simple  alimentary  canal  in  its  upper  and  lower  portions. 
Immediatelv  beneath  the  right  hand  i  is  seen  the  f  oetal  heart,  lying  in  the  anterior  part 
of  the  pleuro-peritoneal  cavity  ;  v,  the  yolk-sac,  or  umbilical  vesicle  ;  v  i,  the  vitello- 
intestinal  opening ;  u,  the  allantois  connected  by  a  pedicle  with  the  anal  portion  of 
the  alimentary  canal  (From  Quain's  "Anatomy"). 


ohap.  xx.]  PCETAL  MEMBRANES,  767 

This  moat  runs  in  further  and  further  all  round  beneath  the 
overhanging  embryo,  till  the  latter  comes  to  resemble  a  canoe 
turned  upside-down,  the  ends  and  middle  being,  as  it  were, 
decked  in  by  the  folding  or  tucking  in  of  the  blastoderm,  while 
on  the  ventral  surface  there  is  still  a  large  communication  with 
the  yelk,  corresponding  to  the  "  well "  or  undecked  portion  0f 
the  canoe. 

'Phis  communication  between  the  embryo  and  the  yelk  is  gra- 
dually contracted  by  the  further  tucking  in  of  the  blastoderm 
from  all  sides,  till  it  becomes  narrowed  down,  as  by  an  invisible 
constricting  band,  to  a  mere  pedicle  which  passes  out  of  the  body 
of  the  embryo  at  the  point  of  the  future  umbilicus. 

Visceral  Plates. — The  downwardly  folded  portions  of  blasto- 
derm are  termed  the  visceral  plates. 

Thus  we  see  that  the  body-cavity  is  formed  by  the  downward 
folding  of  the  visceral  plates,  just  as  the  neural  cavity  is  pro- 
duced by  the  upward  growth  of  the  dorsal  laminae,  the  difference 
being  that,  in  the  visceral  or  ventral  lamina),  all  three  layers  of 
the  blastoderm  are  concerned. 

The  folding  in  of  the  splanchnopleure,  lined  by  hypoblast, 
pinches  off,  as  it  were,  a  ptortion  of  the  yelk-sac,  enclosing  it  in  the 
body-cavity.  This  forms  the  rudiment  of  the  alimentary  canal, 
which  at  this  period  ends  blindly  towards  the  head  and  tail,  while 
in  the  centre  it  communicates  freely  with  the  cavity  of  the  yelk- 
sac  through  the  canal  termed  vitelline  or  omphdlo-mesenteric  duct. 

The  yelk-sac  thus  becomes  divided  into  two  portions  which 
communicate  through  the  vitelline  duct,  that  portion  within  the 
body  giving  rise,  as  above  stated,  to  the  digestive  canal,  and  that 
outside  the  body  remaining  for  some  time  as  the  umbilical  vesicle 
(fig.  417,  ys).  The  hypoblast  forming  the  epithelium  of  the 
intestine  is  of  course  continuous  with  the  lining  membrane  of 
the  umbilical  vesicle,  while  the  visceral  plate  of  the  mesoblast 
is  continuous  with  the  outer  layer  of  the  umbilical  vesicle. 

All  the  above  details  will  be  clear  on  reference  to  the  accom- 
panying diagrams. 

Foetal  Membranes. 

Umbilical  Vesicle  or  Yelk-sac. — The  splanchnopleure,  lined 
by  hypoblast,  forms  the  yelk-sac  in  Reptiles,  Birds,  and  Mammals; 


y68 


GENERATION    AND    DEVELOPMENT. 


[chap.  XX. 


but  in  Amphibia  and  Fishes,  since  there  is  neither  amnion  nor 
alhmtois,  the  Avail  of  the  yelk-sac  consists  of  all  three  layers  of 


Fig.  417. — Dior/rams,  showing  three  successive  stages  of  development.  Transverse  vertical 
sections.  The  yelk-sac,  ys,  is  seen  progressively  diminishing  in  size.  In  the  eml  >rv<  > 
itself  the  medullary  canal  and  notochord  are  seen  in  section,  a',  in  middle  figure,  the 
alimentary-  canal,  becoming  pinched  off,  as  it  -were,  from  the  yelk-sac ;  a',  in  right  hand 
figure,  alimentary  canal  completely  closed;  a,  in  last  two  figures,  amnion;  oc,  cavity 
of  amnion  filled  with  amniotic  fluid  ;  pp,  space  between  amnion  and  chorion,  con- 
tinuous with  the  pleuro-peritoneal  canty  inside  the  bodv ;  vt,  vitelline  membrane  ;  ys, 
5-elk-sac,  or  umbilical  vesicle  (Foster  and  Balfour). 

the    blastoderm,   enclosed,    of   course,  by    the    original    vitelline 
membrane. 

The  body  of  the  embryo  becomes  in  great  measure  detached 
from  the  yelk-sac  or  umbilical  vesicle,  which  contains,  however. 


Fig.  418. — Diagram  showing  vascular  area 
in  the  chick,  a,  area  pellucida  ;  b,  area 
vasculosa ;  c,  area  vitellina. 


Fig.  419. — Human  embryo  of  fifth  week 
with  umbilical  vesicle;  about  natural 
size  (Daltonl.  The  human  umbilical 
vesicle  never  exceeds  the  size  of  a 
small  pea. 


the  greater  part  of  the  substance  of  the  yelk,  and  furnishes  a 
source  whence  nutriment  is  derived  for  the  embryo.  This  nutri- 
ment is  absorbed  by  the  numerous  vessels  (omphalomesenteric) 
which  ramify  in  the  walls  of  the  yelk-sac,  forming  what  in  birds 
is  termed  the  area  vasculosa.     In  Birds,  the  contents  of  the  yelk- 


.  H.M-.  xx.]  FCETAL    MEMBRANES,  769 

sac  afford  nourishment  until  the  end  of  incubation,  and  the 
omphalo-mesenteric    vessels   arc    developed    to   a    corresponding 

degree;    but  in  Mammalia    the    office    of  the    umbilical    vesicle 

a  at  a  verj  early  period,  the  quantity  of  the  yelk  is  small,  and 

the  embryo  booh  becomes  independent  of  it  by  the  connections  it 

forms  with  the  parent.  Moreover,  in  Birds,  as  the  sac  is 
emptied,  it  is  gradually  drawn  into  the  abdomen  through  the 
umbilical  opening,  which  then  closes  over  it  :  but  in  Mammalia 
it  always  remains  on  the  outside;  and  as  it  is  emptied 
it  contracts  (fig.  419),  shrivels  up,  and  together  with  the 
part  of  its  duct  external  to  the  abdomen,  is  detached  and  dis- 
appears either  before  or  at  the  termination  of  intra-uterine 
life,  the  period  of  its  disappearance  varying  in  different  orders  of 
Mammalia. 

When  blood-vessels  begin  to  be  developed,  they  ramify  largely 
over  the  walls  of  the  umbilical  vesicle,  and  are  actively  concerned 
in  absorbing  its  contents  and  conveying  them  away  for  the 
nutrition  of  the  embryo. 

The  Amnion  and  Allantois. — At  an  early  stage  of  develop- 
ment of  the  foetus,  and  some  time  before  the  completion  of  the 
changes  which  have  been  just  described,  two  important  structures, 
called  respectively  the  amnion  and  the  allantois,  begin  to  be  formed. 

Amnion. — The  amnion  is  produced  as  follows  : — Beyond  the 
head-  and  tail-folds  before  described  (p.  765),  the  somatopleure 
coated  by  epiblast,  is  raised  into  folds,  which  grow  up,  arching 
over  the  embryo,  not  only  anteriorily  and  posteriorly  but  also 
laterally,  and  all  converging  towards  one  point  over  its  dorsal 
surface  (fig.  417).  The  growing  up  of  these  folds  from  all  sides 
and  their  convergence  towards  one  point  very  closely  resembles 
the  folding  inwards  of  the  visceral  plates  already  described,  and 
hence,  by  some,  the  point  at  which  the  amniotic  folds  meet  over 
the  back  has  been  termed  the  "  amniotic  umbilicus." 

The  folds  not  only  come  into  contact  but  coalesce.  The  inner 
of  the  two  layers  fomis  the  true  amnion,  while  the  outer  or 
reflected  layer,  sometimes  termed  the  false  amnion,  coalesces  with 
the  inner  surface  of  the  original  vitelline  membrane  to  form  the 
chorion.  This  growth  of  the  amniotic  folds  must  of  course  be 
clearly    distinguished    from    the    very    similar    process,    already 

3  D 


// 


O  GENERATION    AND    DEVELOPMENT.  [chap.  xx. 


described,  by  which  the  walls  of  the  neural  canal  are  formed  at 
a  much  earlier  stage. 

Amniotic  C  vty. — The  cavity  between  the  true  amnion  and  the 
external  surface  of  the  embryo  becomes  a  closed  space,  termed  the 
amniotic  cavity  (ac,  fig.  417). 

At  first,  the  amnion  closely  invests  the  embryo,  but  it  becomes 
gradually  distended  with  fluid  (liquor  amnii),  which,  as  preg- 
nancy advances,  reaches  a  considerable  quantity. 

This  fluid  C'  osists  :  water  containing  small  quantities  of  albumen  and 
urea.  Its  chief  function  during  gestation  appears  to  be  the  mechanical  one 
of  affording  equal  support  to  the  embryo  on  all  sides,  and  of  protecting  it  as 
far  as  possible  from  the  effects  of  blows  and  other  injuries  to  the  abdomen 
of  the  mother. 

The  embryo  up  to  the  end  of  pregnancy  is  thus  immersed  in  fluid,  which 
during  parturition  serves  the  important  purpose  of  gradually  and  evenly 
dilating  the  neck  of  the  uterus  to  allow  of  the  passage  of  the  foetus  :  when 
this  is  accomplished  the  amniotic  sac  bursts  and  the  "  waters  "  escape. 

On  referring  to  the  diagrams  (fig,  4171.  it  will  be  obvious  that 
the  cavity  outside  the  amnion  (between  it  and  the  false  amnion) 
is  continuous  with  the  pleuro-peritoneal  cavity  at  the  umbilicus. 
This  cavity  is  not  entirely  obliterated  even 
at  birth,  and  contains  a  small  quantity  of 
fluid  ("  false  waters"),  which  is  discharged 
during  parturition  either  before,  or  at  the 
same  time  as  the  amniotic  fluid. 

Allantois. — Into  the  pleuro-peritoneal  space 
the  allantois  sprouts  out,  its  formation  com- 
a  mencing    during    the    development     of    the 

Tig.    420— Diagram     of       amnion. 
'-  1  egg.   a,  um- 
bilical vesicle;  b  am-  Growing  out  from  or  near  the  hinder  por- 

motic  cavity  :  -:,  allan-  * 

tois  Daiton  .  tion  of  the  intestinal  canal  (c,  fig.  420),  with 

which  it  communicates,  the  allantois  is  at 
first  a  solid  pear-shaped  mass  of  splanchnopleure  :  but  becoming 
vesicular  by  the  projection  into  it  of  a  hollow  out-growth  of 
hypoblast,  and  very  soon  simply  membranous  and  vascular,  it 
insinuates  itself  between  the  amniotic  folds,  just  described,  and 
comes  into  close  contact  and  union  with  the  outer  of  the  two 
folds,  which  has  itself,  as  before  said,  become  one  with  the  ex- 
ternal investing  membrane  of  the  egg.  As  it  grows,  the  allantois 
developes  muscular  tissue  in  its  external    wall  and  becomes  ex- 


CHAP.   XX. 1 


THE    CHOBION. 


7/i 


oeedingly  vascular;    in  birds  (fi.ur.  421)    it    envelopes  the  whole 
embryo— taking  up  vessels,  so  to  speak,  to  the  outer  investing 
membrane  of  the  egg:  and  lining  the  inner  surface  of  the  aheU 
with  a  vascular  membrane,  by  these  means 
affording  an  extensive  surface  in  which  the 
blood  may  be  aerated.     In  the  human  sub- 
ject   and   in   other  Mammalia,    the  v< 
carried  out  by  the  allantois  are  distributed 
only  to  a  special  part  of  the  outer  mem- 
brane or  chorion,  where,  by  interlacement 
with  the  vascular  system  of   the  mother. 
a  structure  called  the  placenta  is  developed. 

In  Mammalia,  as  the  visceral  lamina? 
close  in  the  abdominal  cavity,  the  allantois 
is  thereby  divided  at  the  umbilicus  into 
two  portions  ;  the  outer  part,  extending 
from  the  umbilicus  to  the  chorion,  soon 
shrivelling ;  while  the  inner  part,  remain- 
ing in  the  abdomen,  is  in  part  converted 
into  the  urinary  bladder  ;  the  portion  of 
the  inner  part  not  so  converted,  extending 
from  the  bladder  to  the  umbilicus,  under 
the  name  of  the  urachus.     After  birth  the 

umbilical  cord,  and  with  it  the  external  and  shrivelled  portion 
of  the  allantois,  are  cast  off  at  the  umbilicus,  while  the  urachus 
remains  as  an  impervious  cord  stretched  from  the  top  of  the 
urinary  bladder  to  the  umbilicus,  in  the  middle  line  of  the  body, 
immediately  beneath  the  parietal  layer  of  the  peritoneum.  It  is 
sometimes  enumerated  among  the  ligaments  of  the  bladder. 

It  must  not  be  supposed  that  the  phenomena  which  have  been 
successively  described,  occur  in  any  regular  order  one  after 
another.  On  the  contrary,  the  development  of  one  part  is  going 
on  side  by  side  with  that  of  another. 

The  Chorion. — It  has  been  already  remarked  that  the  allantoic 
is  a  structure  which  extends  from  the  body  of  the  foetus  to  the 
outer  investing  membrane  of  the  ovum,  that  it  insinuates  itself 
between  the  two  layers  of  the  amniotic  fold,  and  becomes  fused 
with  the  outer  layer,  which  has  itself  become  previously  fused 
with   the    vitelline    membrane.       By   these    means    the    external 

3  i>  2 


Fig1.  421.  —  Fecundated   eya 
with  allantois  nearly  eom- 

o,  inner  layer  of 
amniotic  fold ;  b,  outer 
layer  of  ditto :  c.  point 
where  the  amniotic  folds 
come  in  contact.  The 
allantois  is  seen  penetrat- 
ing between  the  outer 
and  inner  layers  of  the 
amniotic  folds.  This 
figure,  which  represents 
only  the  amniotic  folds 
and  the  parts  within 
them,  should  be  compared 
with  figs.  417,  423,  in 
which  will  be  found  the 
stiu-tures  external  to 
these  folds  (Dalton  . 


772 


GENERATION  AND  DEVELOPMENT. 


[chap.  XX. 


investing  membrane  of  the  ovum,  or  the   chorion,  as  it  is  now 
called,    represents   three   layers,    namely,    the    original    vitelline 


Figs.  4 22  and  423  (after  Todd  ami  Bowman),  a,  chorion  with  villi.  The  villi  are  shown 
to  be  best  developed  in  the  part  of  the  chorion  to  which  the  allantois  is  extending  ; 
this  portion  ultimately  becomes  the  placenta  ;  b,  space  between  the  two  layers  of  the 
amnion  ;  c,  amniotic  cavity ;  d,  situation  of  the  intestine,  showing  its  connection  with 
the  umbilical  vesicle ;  e,  umbilical  vesicle ;  /,  situation  of  heart  and  vessels  ;  g 
allantois. 

membrane,    the    outer    layer    of    the    amniotic    fold,    and    the 
allantois. 

Very  soon  after  the  entrance  of  the  ovum  into  the  uterus,  in 
the  human  subject,  the  outer  surface    of  the  chorion  is  found 

beset  with  fine  processes,  the  so-called 
villi  of  the  chorion  (a,  figs.  422,  423), 
which  give  it  a  rough  and  shaggy 
appearance.  At  first  only  cellular  in 
structure,  these  little  outgrowths  sub- 
sequently become  vascular  by  the  de- 
velopment in  them  of  loops  of  capil- 
laries (fig.  423);  and  the  latter  at 
length  form  the  minute  extremities  of 
the  blood-vessels  which  are,  so  to  speak, 
conducted  from  the  fcetus  to  the  chorion 
by  the  allantois.  The  function  of  the 
villi  of  the  chorion  is  evidently  the 
absorption  of  nutrient  matter  for  the 
fcetus ;  and  this  is  probably  supplied  to  them  at  first  from 
the  fluid  matter,  secreted  by  the  follicular  glands  of  the 
uterus,  in  which   they  are    soaked.      Soon,  however,   the    foetal 


Fig.  424. 


OH  A  P.  xx.] 


FORMATION    OF    PLACENTA. 


771 


lis  of  the  villi  oome    into  more  intimate  relation  with  the 

Is  of  the  uterus.     The  pari   at  which  this  relation  between 

the  vessels  of  the  foetus  and  those  of  the  parenl  ensues,  is  not, 

however,  ever  the   whole  Surface  of  the  chorion:   for,  although   all 

the  villi  become  vascular,  yet  they  become  indistinct  or  disappear 

except  ;it  one  pari  where  ihey  are  greatly  developed,  and  by  their 
branching  give  rise,  with  the  vessels  of  the  uterus,  to  the  forma- 
tion of  the  plaCi  lit*'. 

To  understand  the  manner  in  which  the  fatal  and  maternal 
blood-vessels  come  into  relation  with  each  other  in  the  placenta, 
it  is  necessary  briefly  to  notice  the  changes  which  the  uterus 
undergoes  after  impregnation.  These  changes  consist  especially 
of  alterations  in  structure  of  the  superficial  part  of  the  mucous 
membrane  which  lines  the  interior  of  the  uterus,  and  which 
forms,  after  a  kind  of  development  to  he  immediately  described, 
the  membrana  decidua,  so  called  on  account  of  its  being  discharged 
from  the  uterus  at  birth. 

Formation  of  the  Placenta. 

The  mucous  membrane  of  the  human  uterus,  which  consists 
of  a  matrix  of  connective  tissue   containing  numerous  corpuscles 


Fur.  42;. — Section   of  the  lining  membrane  of  a  human   uterus  at  the   period  of  commencing 

win-'  tin'  arrangement  and  other  peculiarities  of  the  glands,  </.  <l,  j, 
■with  their  orifices,  ",  »,  a,  on  the  internal  sulfate  of  the  organ.  Twice  the  natural  size. 

(adenoid  tissue),  and  is  lined  internally  by  columnar  ciliated 
epithelium,  is  abundantly  beset  with  tubular  glands,  arranged 
perpendicularly  to  the  surface  (fig.  425).  These  follicles  are  very 
small  in  the  unimpregnated  uterus ;  but  when  examined  shortly 
after  impregnation,  they  are  found  elongated,  enlarged,  and  much 
waved  and  contorted  towards  their  deep  and  closed  extremity, 


774 


GENERATION  AND  DEVELOPMENT. 


[CHAT.    XX. 


which  is  implanted  at  some  depth  in  the  tissue  of  the  uterus,  and 
may  dilate  into  two  or  three  closed  sacculi  (fig.  425). 

The  glands  are  lined  by  columnar  ciliated  epithelium,  and  they 
open  on  the  inner  surface  of  the  mucous  membrane  by  small  round 
orifices  set  closely  together  (a,  a,  fig.  426). 

On  the  internal  surface  of  the  mucous  membrane  may  be  seen 
the  circular  orifices  of  the  glands,  many  of 
which  are,  in  the  early  period  of  pregnancy, 
surrounded  by  a  whitish  ring,  formed  of 
the  epithelium  which  lines  the  follicles 
(fig.  426). 

Membrana  decidua.— Coincidently  with 
the  occurrence  of  pregnancy,  important 
changes  occur  in  the  structure  of  the  mucous 
membrane  of  the  uterus.  The  epithelium 
and  sub-epithelial  connective  tissue,  toge- 
ther with  the  tubular  glands,  increase  rapidly, 
and  there  is  a  greatly  increased  vascularity 
of  the  whole  mucous  membrane,  the  vessels 
of  the  mucous  membrane  becoming  larger 
and  more  numerous ;  while  a  substance 
composed  chiefly  of  nucleated  cells  fills  up 
the  interfollicular  spaces  in  which  the  blood- 
vessels are  contained.  The  effect  of  these 
changes  is  an  increased  thickness,  softness, 
and  vascularity  of  the  mucous  membrane, 
the  superficial  part  of  which  itself  forms 
the  membrana  decidua. 

The  object  of  this  increased  development 
seems  to  be  the  production  of  nutritive 
materials  for  the  ovum  ;  for  the  cavity  of 
the  uterus  shortly  becomes  filled  with 
secreted  fluid,  consisting  almost  entirely  of  nucleated  cells  in 
which  the  villi  of  the  chorion  are  imbedded. 

When  the  ovum  first  enters  the  uterus  it  becomes  imbedded  in 
the  structure  of  the  decidua,  which  is  yet  quite  soft,  and  in  which 
soon  afterwards  three  portions  are  distinguishable.  These  have 
been  named  the  decidua  vera,  the  decidua  reflexa,  and  the  decidua 
serotina.     The  first  of  these,  the  decidua  vera,  lines  the  cavity  of 


Fig.  426. — Two  thin  segments 
of  human  decidua  after 
recent  impregnation,  view- 
ed on  a  dark  ground : 
they  show  the  openings 
on  the  surface  of  the 
membrane,  a  is  magni- 
fied six  diameters,  and 
b  twelve'  diameters.  At 
1,  the  lining  of  epithe- 
lium is  seen  within  the 
orifices,  at  2  it  has  es- 
caped (Sharpey). 


CHAP.   XX.] 


THE    PLACENTA. 


775 


the  uterus  ;  the  second,  or  deoidua  reflexa,  is  a  part  of  the  decidua 

vera  which    -tows   up  around   the   ovum,  and,  wrapping  it  closely, 
tonus  its  immediate  investment. 

The  third,  or  decidua  serotina,  is  the  part  of  the  decidua  vera 
which  becomes  especially  developed  in  connection  with  those  vill 


Fi01.  427. — Diagrammatic  view  of  a  vertical  transverse  section  of  the  uterus  <d  the  seventh  or 

eighth  week  of  pregnancy,  c,  c,  c',  cavity  of  uterus,  which  becomes  the  cavity  of  the 
decidua,  opening  at  c,  r,  the  cornua,  into  the  Fallopian  tubes,  and  at  c  into  the  cavity 
of  the  cervix,  which  is  closed  by  a  plug  of  mucus ;  d  v,  decidua  vera ;  d  r,  decidua 
reflexa,  with  the  sparser  villi  imbedded  in  its  substance;  d  s,  decidua  serotina,  in- 
volving the  more  developed  chorionic  villi  of  the  commencing  placenta.  The  foetus  is 
seen  lying  in  the  amniotic  sac ;  passing  up  from  the  umbilicus  is  seen  the  umbilical 
cord  and  its  vessels,  passing  to  their  distribution  in  the  villi  of  the  chorion  ;  also  the 
pedicle  of  the  yelk  sac,  which  lies  in  the  cavity  between  the  amnion  and  chorion  (Allen 
Thomson) . 

of  the  chorion,  which,  instead  of  disappearing,  remain  to  form  the 
fcetal  part  of  the  placenta. 

In  connection  with  these  villous  processes  of  the  chorion,  there 
are  developed  depressions  or  crypts  in  the  decidual  mucous  mem- 
brane, which  correspond  in  shape  with  the  villi  they  are  to  lodge  ; 
and  thus  the  chorionic  villi  become   more  or  less  imbedded  in  the 


n 


GENERATION    AXD    LEVEL'  >PMEXT. 


.  xx. 


maternal  structures.  These  uterine  crypts,  it  La  important  to 
note,  are  not,  as  was  once  supposed,  merely  the  open  mouths  of 
the  uterine  follicles  (Turner). 

Aa  the  ovuni  increases  in  size,  the  decidua  vera  and  the  decidua 
reflexa  gradually  come  into  contact,  and  in  the  third  month  of 
pregnane  en  them  has  quite  disappeared.     Hence- 

forth it  is  very  difficult,  or  even  impossible,  to  distinguish  the 
t 

The  Placenta. — During  these  changes  the  deeper  part  of  the 
mucous  membrane  of  the  uterus,  at  and  near  the  region  where 
the  placenta  is  placed,  becomes  hollowed  out  by  sinuses,  or 
.  which  communicate  on  the  one  hand  with 
arteries  and  on  the  other  with  reins  of  the  uterus.  Into  these 
sinuses  the  villi  of  the  chorion  protrude,  pushing  the  1  <.»f 

the    sinus    before    them,    and    so    come 
into    intimate    relation  with    the    bl 
contained  in  them.      The:      is  n 
communication  L-vesseta 

of  the  mother  and  tho^e  of  the  fcetus  ; 
but   the    layer    or    layers    of  membrane 
intervening  between  the  blood  of  the  one 
and  of  the  other  offer  no  obstacle  t 
interchange    of  matters    between    them. 
Thus   t       villi  of  the  chorion  containi 
foetal  blood,  are  bathed  or  soaked  in 
mil  blood  contained  in  the  uterine  sinu  - 
The  arrangement  may  be  roughly  com- 
pared to  filling       _  foetal  blood, 
and  clipping  its  fingers  into  a  vessel  c 
But  in         foetal  villi  then  is  tstant 
stream  of  blood  into  and  out  of  the  loop  of  capillary  blood-  con- 
tained in  it,  as  there  is  also  into  and  out  of  the  maternal  sinu-  js. 

It  would  seem  froin  the  observati  :    G  :.   that,   at  the 

villi  of  the  placental  tufts,  where  the  foetal  and  maternal 
of  the  placenta  are  brought  int  elation  with   each  ot 

the  blood  in  the  vessels  of  the  m :  orated  from 

the  vessels  of  the  foetus  by  the  intervention  of  two  distinct 
of  nucleated   cells  (fig.  428).     One   of  these  ngs  the 

maternal  portion  of  the  phi 


-  •  — Ezirtmity  of  a  pia- 
tental  tiHvs.  o,  Hning-  mem- 
brane of  the  vascular  system 
of  the  mother ;  b,  cells  imme- 
_--  •'■^-7    -:.:.-  .»:.-..-. 

between  the  maternal  and 
foetal  portions  of  the  villus ; 
e.  internal  membrane  of  the 
V:-V~.  ::  -.-■;-- ::. -/_ :..-:.." ;■>.:_- 
of  the  chorion:  f.  internal 
cdls  of  the  villus',  or  cells  of 

-    .  - 


!ng  maternal  blood. 


i  bap.  xx.  1  THE    PLACENTA. 


in 


of  the  villus  and  thai  of  the  vascular  system  of  the  mother,  and 
is  probablj  designed  to  separate  from  the  blood  of  the  parent  th< 
materials  destined  for  the  blood  "f  the  fretus;  the  other  (/') 
belongs  to  the  foetaJ  portion  of  the  placenta,  i  Bituated  between 
the  membrane  of  the  villus  and  the  loop  of  vessels  contained 
within,  and  probably  serves  for  the  absorption  of  the  material 
secreted  by  the  other  sets  of  cells,  and  for  its  conveyance  into  the 
blood-vessels  of  the  foetus.  Between  the  two  sets  <>f  cells  with 
their  investing  membrane  there  exists  a  space  (d),  into  which  it 
is  probable  that  the  materials  secreted  by  the  one  set  of  cells  of 
the  villus  are  poured  in  order  that  they  may  he  absorbed  by  the 
other  set,  and  thus  conveyed  into  the  fcetal  vessels. 

Not  only,  however,  is  there  a  passage  of  materials  from  the 
blood  of  the  mother  into  that  of  the  foetus,  but  there  is  a  mutual 
interchange  "f  materials  between  the  blood  both  of  fcetus  and  of 
parent  ;  the  latter  supplying  the  former  with  nutriment,  and  in 
turn  abstracting  fr.au  it  materials  which  require  to  be  removed 

Alexander  Harvey's  experiments  were  very  decisive  on  this  point.  The 
view  ha-  also  received  abundant  support  from  Hutchinson's  important  ob- 
servations on  the  communication  of  syphilis  from  the  father  to  the  mother, 
through  the  instrumentality  of  the  feetu-  :  and  still  more  from  Savory's 
experimental  researches,  which  prove  quite  clearly  that  the  female  parent 
may  be  directly  inoculated  through  the  foetus.  Having  opened  the  abdomen 
and  uterus  of  a  pregnant  bitch,  Savory  injected  a  solution  of  strychnia  into 
the  abdominal  cavity  of  one  foetus,  and  into  the  throracic  cavity  of  another, 
and  then  replaced  all  the  part-,  every  precaution  being  taken  to  prevent 
escape  of  the  poison.  In  less  than  half  an  hour  the  bitch  died  from  tetanic 
spasms  :  the  foetuses  operated  on  were  also  found  dead,  while  the  others. 
alive  and  active.  The  experiments,  repeated  on  other  animals  with 
like  results,  leave  n<>  doubt  of  the  rapid  and  direct  transmission  of  matter 
from  the  foetus  to  the  mother,  through  the  blood  of  the  placenta. 

The  placenta,  therefore,  of  the  human  subject  is  composed  of  a 
fetal  part  and  a  maternal  part, — the  term  placenta  properly  in- 
cluding all  that  entanglement  of  fcetal  villi  and  maternal  sinuses, 
by  means  of  which  the  blood  of  the  fcetus  is  enriched  and  purified 
after  the  fashion  necessary  for  the  proper  growth  and  develop- 
ment of  those  parts  which  it  is  designed  to  nourish. 

Tip-  importance  of  the  placenta  i-  at  once  apparent  if  we  remember  that 
during  the  greater  portion  of   intra-uterine  life  the  maternal  blood  circu- 
lating in  it-  v<  .'lie-  the  foetus  with  I  I  and  oxygen.     It  thu- 
rms  the  functions  which  in  later  life  are  discharged  by  the  alimentarv 
canal  and  Lungs. 


7;8  GENERATION    AND    DEVELOPMENT.  [chap.  xx. 

The  whole  of  this  structure  is  not,  as  might  be  imagined,  thrown 
off  immediately  after  birth.  The  greater  part,  indeed,  comes  away 
at  that  time,  as  the  after-birth  :  and  the  separation  of  this  por- 
tion takes  place  by  a  rending  or  crushing  through  of  that  part  at 
which  its  cohesion  is  least  strong,  namely,  where  it  is  most  bur- 
rowed and  undermined  by  the  cavernous  spaces  before  referred  to. 
In  this  way  it  is  cast  off  with  the  foetal  membrane  and  the  decidua 
vera  and  reflesa,  together  with  a  part  of  the  decidua  serotina,  The 
remaining  portion  withers,  and  disappears  by  being  gradually 
either  absorbed,  or  thrown  off  in  the  uterine  discharges  or  the 
lochia,  which  occur  at  this  period. 

A  new  mucous  membrane  is  of  course  gradually  developed,  as 
the  old  one,  by  its  peculiar  transformation  into  what  is  called  the 
decidua,  ceases  to  perform  its  original  functions. 

The  umbilical  cord,  which  in  the  latter  part  of  foetal  life  is  almost 
solely  composed  of  the  two  arteries  and  the  single  vein  which  respec- 
tively convey  foetal  blood  to  and  from  the  placenta,  contains  the 
remnants  of  other  structures  which  in  the  early  stages  of  the 
■development  of  the  embryo  were,  as  already  related,  of  great  com- 
parative importance.  Thus,  in  early  foetal  life,  it  is  composed  of 
the  following  parts  : — (i.)  Externally,  a  layer  of  the  amnion, 
reflected  over  it  from  the  umbilicus.  (2.)  The  umbilical  vesicle 
with  its  duct  and  appertaining  omphalo-mesenteric  blood-vessels. 
(3.)  The  remains  of  the  allantois,  and  continuous  with  it  the 
urachus.  (4.)  The  umbilical  vessels,  which,  as  just  remarked* 
ultimately  form  the  greater  part  of  the  cord. 

Development  of  Organs. 

It  remains  now  to  consider  in  succession  the  development  of  the 
several  organs  and  systems  of  organs  in  the  further  progress  of 
the  embryo.  The  accompanying  figure  (fig.  429)  shows  the  chief 
organs  of  the  body  in  a  moderately  early  stage  of  development. 

Development  of  the  Vertebral  Column    and  Cranium. 

The  primitive  part  of  the  vertebral  column  in  all  the  Yerte- 
brata  is  the  chorda  dorsalis  (notochord),  which  consists  entirely  of 
soft  cellular  cartilage.  This  cord  tapers  to  a  point  at  the  cranial 
and  caudal  extremities  of  the   animal.      In  the    progress    of    its 


CHAP.    \\. 


DEVELOPMENT    OF    SPINAL    COLUMN. 


779 


development,  it  is  found  to  become  enclosed  in  a  membranous 
sheath,  which  al  Length  acquires  a  fibrous  structure,  composed  of 
transverse  annular  fibres.  The  chorda  dorsalis  is  to  be  regarded 
as  the  azygos  axis  of  the  spinal  column,  and,  in  particular,  of  the 
future  bodies  of  the  vertebrae,  although  it  never  itself  passes  into 
the  Btate  of  hyaline  cartilage  or  bone,  but  remains  enclosed  as  in 


Tjsr 


2y\       GmYjWir      if 

/  y 


Fig.  429. — Embryo  chick  (4th  day),  vu  wed  as  a  transpareat  object,  lying  on  its  left  side  (mag- 
nified). G  If,  cerebral  hemispheres  ;  F  B,  fore-brain  or  vesicle  of  third  ventricle,  with 
Pn,  pineal  eland  projecting  from  its  summit;  M  H.  mid-brain;  C  b,  cerebellum; 
IV  J ',  fourth  ventricle ;  L,  lens;  ch  s,  choroidal  slit ;  Cen  V,  auditoiy  vesicle  ;  ««, 
superior  maxillary  process  ;  iF,  2F,  Sec,  first,  second,  third,  and  fourth  visceral  folds  ; 
J',  fifth  nerve,  sending  one  branch  (ophthalmic)  to  the  eye,  and  another  to  the  first 
visceral  arch  ;  VII,  seventh  nerve,  passing  to  the  second  visceral  arch  ;  G  Ph,  glosso- 
pharyngeal nerve,  passing  to  the  third  visceral  arch ;  P  g,  pneumogastric  nerve, 
passing  towards  the  fourth  visceral  arch  ;  i  v,  investing  mass;  <•  h,  notochord;  its 
front  end  cannot  be  seen  in  the  living  embryo,  and  it  does  not  end  as  shown  in  the 
figure,  but  takes  a  sudden  bend  downwards,  and  then  terminates  in  a  point ;  II  t, 
heart  seen  through  the  walls  of  the  chest;  M  P,  muscle-plates;  W,  wing,  showing 
commencing  differentiation  of  segments,  corresponding  to  ana,  forearm,  and  hand  ; 
//  L,  hind-limb,  as  yet  a  shapeless  bud,  showing  no  differentiation.  Beneath  it  is  seen 
the  curved  tail  (Foster  and  Balfour). 

ii  case  within  the  persistent  parts  of  the  vertebral  column  which 
are  developed  around  it.  It  is  permanent,  however,  only  in  a  few 
animals  :  in  the  majority  only  traces  of  it  persist  in  the  adult 
animal. 

In  many  Fish  no  true  vertebras  are  developed,  and  there  is 
every  gradation  from  the  amphioxus,  in  which  the  notochord  per- 
sists through  life  and  there  are  no  vertebral  segments,  through 
the  lampreys  in  which  there  are  a  few  scattered  cartilaginous  seg- 
ments, and  the  sharks,  in  which  many  of  the  vertebra?   are  partly 


j%0  GENERATION    AND    DEVELOPMENT.  [chap.  xx. 

ossified,  to  the  bony  fishes,  such  as  the  cod  and  herring,  in  which 
the  vertebral  column  consists  of  a  number  of  distinct. ossified  ver- 
tebrae, with  remnants  of  the  notochord  between  them.  In 
Amphibia,  Reptiles,  Birds,  and  Mammals,  there  are  distinct  ver- 
tebra, which  are  formed  as  follows  : — 

Protovertebrse. — The  protovertebrce,  which  have  been  already 
mentioned  (p.  764),  send  processes  downwards  and  inwards  to 
surround  the  notochord,  and  also  upwards  between  the  medullary 
canal  and  the  epiblast  covering  it.  In  the  former  situation,  the 
cartilaginous  bodies  of  the  vertebras  make  their  appearance,  in  the 
latter  their  arches,  which  enclose  the  neural  canal. 

The  vertebras  do  not  exactly  correspond  in  their  position  with 
the  protovertebrse  :  but  each  permanent  vertebra  is  developed 
from  the  contiguous  halves  of  two  protovertebrse.  The  original 
segmentation  of  the  protovertebrse  disappears  and  a  fresh  subdi- 
vision occurs  in  such  a  way  that  a  permanent  invertebral  disc  is 
developed  opposite  the  centre  of  each  protovertebra.  Meanwhile 
the  protovertebrse  split  into  a  dorsal  and  ventral  portion.  The 
former  is  termed  the  musculo-cutaneous  plate,  and  from  it  are 
developed  all  the  muscles  of  the  back  together  with  the  cutis  of 
the  dorsal  region  (the  epidermis  being  derived  from  the  epiblast). 
The  ventral  portions  of  the  protovertebrse,  as  we  have  already 
seen,  give  rise  to  the  vertebra  and  heads  of  the  ribs,  but  the  outer 
part  of  each  also  gives  rise  to  a  spinal  ganglion  and  nerve-root. 

The  chorda  is  now  enclosed  in  a  case,  formed  by  the  bodies  of 
the  vertebrae,  but  it  gradually  wastes  and  disappears.  Before  the 
disappearance  of  the  chorda,  the  ossification  of  the  bodies  and 
arches  of  the  vertebras  begins  at  distinct  points. 

The  ossification  of  the  body  of  a  vertebra  is  first  observed  at 
the  point  where  the  two  primitive  elements  of  the  vertebras  have 
united  inferiorly.  Those  vertebras  which  do  not  bear  ribs,  such 
as  the  cervical  vertebras,  have  generally  an  additional  centre  of 
ossification  in  the  transverse  process,  which  is  to  be  regarded  as 
an  abortive  rudiment  of  a  rib.  In  the  foetal  bird,  these  additional 
ossified  portions  exist  in  all  the  cervical  vertebras,  and  gradually 
become  so  much  developed  in  the  lower  part  of  the  cervical  region 
as  to  form  the  upper  false  ribs  of  this  class  of  animals.  The 
same  parts  exist  in  mammalia  and  man  ;  those  of  the  last  cervical 
vertebras  are  the  most  developed,  and  in  children  may,  for  a  con- 


miap.  xx.]       DEVELOPMENT    OF    PITUITARY    BODY.  781 

Biderable  period  be  distinguished  as  a  separate  part  on  each   side, 
like  the  root  or  head  of  a  rib. 

The  true  cranium  is  a  prolongation  of  the  vertebral  column, 
and  is  developed  at  a  much  earlier  period  than  the  facial  bones. 
Originally,  it  is  formed  of  but  one  mass,  a  cerebral  capsule,  the 
chorda  dorsalis  being  continued  into  its  base,  and  ending  there 
with  a  tapering  point.  At  an  early  period  the  head  is  bent  down- 
wards and  forwards  round  the  end  of  the  chorda  dorsalis  in  such  a 
way  that  the  middle  cerebral  vesicle,  and  not  the  anterior,  comes 
to  occupy  the  highest  position  in  the  head. 

Pituitary  Body. — In  connection  with  this  must  be  mentioned 
the  development  of  the  pituitary  body.  It  is  formed  by  the 
meeting  of  two  out-growths,  one  from  the  foetal  brain,  which  grows 
downwards,  and  the  other  from  the  epiblast  of  the  buccal  cavity, 
which  grows  up  towards  it.  The  surrounding  mesoblast  also  takes 
part  in  its  formation.  The  connection  of  the  first  process  with  the 
brain  becomes  narrowed,  and  persists  as  the  infundibulum,  while 
that  of  the  other  process  with  the  buccal  cavity  disappears  com- 
pletely at  a  spot  corresponding  with  the  future  position  of  the 
body  of  the  sphenoid. 

The  first  appearance  of  a  solid  support  at  the  base  of  the 
cranium  observed  by  Muller  in  fish,  consists  of  two  elongated 
bands  of  cartilage  (trabecular  cranii),  one  on  the  right  and 
the  other  on  the  left  side,  which  are  connected  with  the  cartila- 
ginous capsule  of  the  auditory  apparatus,  and  which  diverge  to 
enclose  the  pituitary  body,  uniting  in  front  to  form  the  septum 
nasi  beneath  the  anterior  end  of  the  cerebral  capsule.  Hence,  in 
the  cranium,  as  in  the  spinal  column,  there  are  at  first  developed 
at  the  sides  of  the  chorda  dorsalis  two  symmetrical  elements, 
which  subsequently  coalesce,  and  may  wholly  enclose  the  chorda. 

The  brain-case  consists  of  three  segments  :  occipital,  parietal, 
and  frontal,  corresponding  in  their  relative  position  to  the  three 
primitive  cerebral  vesicles ;  it  may  also  be  noted  that  in  front  of 
each  segment  is  developd  a  sense-organ  (auditory,  ocular,  and 
olfactory,  from  behind  forwards).  The  basis  cranii  consists  at  an 
early  period  of  an  unsegmented  cartilaginous  rod,  developed  round 
the  notochord,  and  continued  forward  beyond  its  termination  into 
the  trabecule  cranii,  which  bound  the  pituitary  fossa  on  either  side 

In  this  cartilaginous  rod  three  centres  of  ossification  appear: 


782 


GENERATION  AXD  DEVELOPMENT. 


[CHAP.   XX. 


basi-occipital,  basi-sphenoid,  and  pre-sphenoid,  one  corresponding 
to  each  segment. 

The  bones  forming  the  vault  of  the  skull  (frontal,  parietal,  squamous 
portion  of  temporal),  with  the  exception  of  the  squamo-occipital,  which  is 
preformed  in  cartilage,  are  ossified  in  membrane. 

Development  of  the  Face  and  Visceral  Arches. 

It  has  been  said  before  that  at  an  early  period  of  development  of 
the  embryo,  there  grow  up  on  the  sides  of  the  primitive  groove  the 
so-called  dorsal  lamince,  which  at  length  coalesce,  and  complete  by 
their  union  the  spinal  canal.  The  same  process  essentially  takes 
place  in  the  head,  so  as  to  enclose  the  cranial  cavity. 

Visceral  lamina?. — The  so-called  visceral  lammee  have  been 
also  described  as  passing  forwards,  and  gradually  coalescing  in 
front,  as  the  dorsal  lamina?  do  behind,  and  thus  enclosing  the 
thoracic  and  abdominal  cavity.  An  analogous  process  occurs  in  the 
facial  and  cervical  regions,  but  the  enclosing  lamina?,  instead  of 
being  simple,  as  in  the  former  instances,  are  cleft. 


Fig.  430. — a.  Magnified  view  from  before  of  the  head  and  neck  of  a  human  embryo  of  about 
three  weeks  (from  Ecker).— 1,  anterior  cerebral  vesicle  or  cerebrum  ;  2,  middle  ditto  ; 
3,  middle  or  fronto-nasal  process  ;  4,  superior  maxillary  process  ;  5,  eye  ;  6,  inferior 
maxillary  process,  or  first  visceral  arch,  and  below  it  the  first  cleft  ;  7,  8,  9,  second, 
third,  and  fourth  arches  and  clefts,  b.  Anterior  view  of  the  head  of  a  human  foetus 
of  about  the  fifth  week  (from  Ecker,  as  before,  fig.  IV.).  1,  2,  3,  5,  the  same  parts  as 
in  a  ;  4,  the  external  nasal  or  lateral  frontal  process  ;  6,  the  superior  maxillary  process  ; 
7,  the  lower  jaw  ;  X ,  the  tongue  ;  8,  first  branchial  cleft  becoming  the  meatus  audi- 
torius  externus. 

In  this  way  the  so-called  visceral  arches  and  clefts  are  formed, 
four  on  each  side  (fig.  430,  a.). 

From  or    in  connection  with    these  arches    the  following  parts  are  de- 
veloped : — 


CUM".    XX.] 


\  [Si  i:i:  \l.    ARCHES. 


733 


The  fir>t  arch  (mandibular)  contains  a  cartilaginous  rod  (Meckel's  carti- 
lage), around  the  distal  end  of  which  the  Lower  jaw  is  developed,  while  the 
malleus  is  ossified  from  the  proximal  end. 

From  near  the  rool  of  this  arch  the  maxillary  procee  forwards  and 

inwanl<  towards  the  middle  line  ;  from  it  are  formed  the  superior  maxilla 
;  1 11*1  malar  bones.    A  pair  of  cartilaginous  rods  (pterygopalatine),  parallel 
to  the  trabecules  cranii,  give  origin  to  the  external  pterygoid  plate  of  the 
sphenoid  and  the  palate  bones. 

The  cleft  between  the  maxillary  process  and  the  mandibular  (or  first 
visceral  arch)  forms  the  mouth. 

When  the  maxillary  processes  on  the  two  sides  fail  partially  or  completely 
to  unite  in  the  middle  line,  the  well-known  eondition  termed  cleft  palatt 
results.      When  the  integument  of  the  face  presents  a  similar  deficiency. 
we  have  the  deformity  known  as  hare-lip.     Though  these    two  deformities 
frequently  co-exist,  they  are  by  no  means  always  necessarily  associated. 

The  upper  part  of  the  face  in  the  middle  line  is  developed  from  the  so- 
called  frontal -nasal  process  ("A.  3.  fig.  430).  From  the  second  arch  are  de- 
veloped the  incus,  stapes,  and  stapedius  muscle,  the  styloid  process  of  the 
temporal  bone,  the  stylo-hyoid  ligament,  and  the  smaller  earn"  of  the  foyoid 
bone.  From  the  third  visceral  arch,  the  greater  cornu  and  body  of  the 
hyoid  bone.  In  man  and  other  mammalia  the  fourth  visceral  arch  is  in- 
distinct.    It  occupies  the  position  where  the  neck  is  afterwards  developed. 

A  distinct  connection  is  traceable  between  these  visceral  arches 
and  certain  cranial  nerves  :   the  trigeminal,  the  facial,  the  glosso- 


vir 


MB 


Fig.  431. — For  description  see  fig.  429. 


pharyngeal,  aud  the  piieuniogastric.     The  ophthalmic  division  of 
the  trigeminal  supplies  the    trabecular  arch  j    the    superior  and 


;84 


GENERATION  AXD  DEVELOPMENT. 


[•  HAP.  XX. 


inferior  maxillary  divisions  supply  the  maxillary  and  mandibular 
arches  respectively. 

The  facial  nerve  distributes  one  branch  (chorda  tympani)  to  the 
first  visceral  arch,  and  others  to  the  second  visceral  arch.  Thus 
it  divides,  enclosing  the  first  visceral  cleft. 

Similarly,  the  glosso-pharyngeal  divides  to  enclose  the  second 
visceral  cleft,  its  lingual  branch  being  distributed  to  the  second, 
and  its  pharyngeal  branch  to  the  third  arch. 

The  vagus,  too,  sends  a  branch  (pharyngeal)  along  the  third  arch, 
and  in  fishes  it  gives  off  paired  branches,  which  divide  to  enclose 
several  successive  branchial  clefts. 

Development  of  the  Extremities. 

The  extremities  are  developed  in  an  uniform  manner  in  all 
vertebrate  animals.     They  appear  in  the  form  of  leaf-like  elevations 


Fig.  432. — A  human  embryo  of  the  fourth  v:e*J:,  3^  lints  in  length. — 1,  the  chorion  ;  3,  part  of 
the  amnion  ;  4,  umbilical  vesicle  with  its  lone  pedicle  passing  into  the  abdomen  ;  7, 
the  heart ;  r-,  the  liver  ;  9,  the  visceral  arch  destined  to  form  the  lower  jaw,  beneath 
which  are  two  other  visceral  arches  separated  by  the  branchial  clefts  ;  10,  rudiment  of 
the  upper  extremity  ;  n,  that  of  the  lower  extremity  :  12.  the  umbilical  cord  ;  15,  the 
eve;  16,  the  ear;  17,  cerebral  hemispheres  ;  18,  optic  lobes,  corpora  quadrigemina 
Mailer). 


from  the  parieties  of  the  trunk  (see  fig.  432),  at  points  where  more 
or  less  of  an  arch  will  be  produced  for  them  within.  The  primitive 
form  of  the  extremity  is  nearly  the  same  in  all  Yertebrata,  whether 
it  be  destined  for  swimming,  crawling,  walking,  or  flying.  In  the 
human  foetus  the  fingers  are  at  first  united,  as  if  webbed  for  swim- 
but  this  is  to  be  regarded  not  so  much  as  an  approximation 


mm£r 


chap,  xx.]  DEVELOPMENT   OF   II  K ART.  785 

to  the  form  of  aquatic  animals,  as  the  primitive  form  of  the  hand, 
the  individual  parts  ofwhich  subsequently  become  more  completely 
isolated. 

The  fore-limb  always  appears  before  the  hind-limb  and  for  some 
time  continues  in  a  more  advanced  state  of  development.  In  both 
limbs  alike,  the  distal  segment  (hand  or  foot)  is  separated  by  a 
slight  notch  from  the  proximal  part  of  the  limb,  and  this  part  is 
subsequently  divided  again  by  a  second  notch  (knee  or  elbow- 
joint). 

Development  of  the  Vascular  System. 

At  an  early  stage  in  the  development  of  the  embryo-chick,  the  so- 
called  "  area  vasculosa"  begins  to  make  its  appearance.  A  number 
of  branched  cells  in  the  mesoblast  send  out  processes  which  unite  so 
as  to  form  a  network  of  protoplasm  with  nuclei  at  the  nodal  points. 
A  large  number  of  the  nuclei  acquire  a  red  colour ;  these  form  the 
red  blood-cells.  The  proto-plasmic  processes  become  hollowed  out 
in  the  centre  so  as  to  form  a  closed  system  of  branching  canals,  in 
the  walls  of  which  the  rest  of  the  nuclei  remain  imbedded.  In 
the  blood-vessels  thus  formed,  the  circulation  of  the  embryonic 
blood  commences. 

According  to  Klein's  researches,  the  first  blood-vessels  in  the  chick 
are  developed  from  embryonic  cells  of  the  mesoblast,  which  swell  up  and 
become  vacuolated,  while  their  nuclei  undergo  segmentation.  These  cells 
send  out  protoplasmic  processes,  which  unite  with  corresponding  ones  from 
other  cells,  and  become  hollowed,  give  rise  to  the  capillary  wall  composed 
of  endothelial  cells  ;  the  blood  corpuscles  being  budded  off  from  the  endo- 
thelial wall  by  a  process  of  gemmation. 

Heart. — About  the  same  time  the  heart  makes  its  appearance 
-  a  solid  mass  of  cells  of  the  splanchnopleure. 

At  this  period  the  anterior  part  of  the  alimentary  tube  ends 
blindly  beneath  the  notochord.  It  is  beneath  the  posterior  end 
of  this  "  fore-gut  "  (as  it  may  be  termed)  that  the  heart  begins  to 
be  developed.  A  cavity  is  hollowed  out  longitudinally  in  the  mass 
of  cells ;  the  central  cells  float  freely  in  the  fluid,  which  soon  begins 
to  circulate  by  means  of  the  rhythmic  pulsations  of  the  embryonic 
heart . 

These  pulsations  take  place  even  before  the   appearance  of  a 

3  E 


;S6 


GENERATION  AND  DEVELOPMENT. 


[CHAP.  XX. 


cavity,  and  immediately  after  the  first  "  laying  down"  of  the  cells 
from  which  the  heart  is  formed,  and  long  before  muscular  fibres  or 
ganglia  have  been  formed  in  the  cardiac  wails.  At  first  they 
seldom  exceed  from  fifteen  to  eighteen  in  the  minute.     The  fluid 

within  the  cavity  of  the  heart 
shortly  assumes  the  characters 
of  blood.  At  the  same  time 
the  cavity  itself  forms  a  com- 
munication with  the  great 
vessels  in  contact  with  it,  and 
the  cells  of  which  its  walls  are 
composed  are  transformed  into 
fibrous  and  muscular  tissues, 
and  into  epithelium.  In  the 
developing  chick  it  can  be 
observed  with   the  naked  eye 

■r 

as  a  minute  red  pulsating 
point  before  the  end  of  the 
second  day  of  incubation. 

Blood-vessels- — Blood-ves- 
sels appear  to  be  developed  in 
two  ways,  according  to  the 
size  of  the  vessels.  In  the 
formation  of  large  blood-ves- 
sels, masses  of  embryonic  cells 
similar  to  those  from  which 
the  heart  and  other  structures 
of  the  embryo  are  developed, 
arrange  themselves  in  the 
position,  form,  and  thickness 
of  the  developing  vessel. 
Shortly  afterwards  the  cells  in 
the  interior  of  a  column  of 
this  kind  seem  to  be  developed 
into     blood-corpuscles,    while 

the  external    layer    of   cells    is  converted   into  the    walls  of  the 
aeL 
Capillaries. — In  the  development  of  capillaries  another  plan  is 

pursued .     This  has  been  well  illustrated  by  Kolliker,  as  observed  in 


Fi?-  433- — Capillary  Hood-vessel*  of  the  tail  of 
a  young  larval  frog,  a,  capillaries  perme- 
able to  blood ;  b,  fat-granules  attached 
to  the  'walls  of  the  vessels,  and  concealing 
the  nuclei ;  c,  hollow  prolongation  of  a 
capillary,  ending  in  a  point :  d ,  a  branch- 
ing cell  -with  nucleus  and  fat-granules  : 
it  communicates  by  three  branches  with 
prolongation  of  capillaries  already 
formed  ;  e.  e,  blood  corpuscles  still  contain- 
ing granules  of  fat.  x  350  times  (Kol- 
liker). 


CM  Al\    XX.  | 


DEVELOPMENT  OF   CAPILLABIE& 


787 


the  tails  of  tadpoles.  The  first  lateral  vessels  of  the  tail  have  the 
form  of  simple  arches,  passing  between  the  main  artery  and  vein,  and 
are  produced  by  the  junc- 
tion of  prolongations,  sent 
from  both  the  artery  and 
vein,  with  certain  elongated 
or  star-shaped  cells,  in  the 
substance  of  the  tail. 
When  these  arches  are 
formed  and  are  permeable 
to  blood,  new  prolonga- 
tions pass  from  them,  join 
other  radiated  cells,  and 
thus  form  secondary  arches 
(fig.  434).  In  this  man- 
ner, the  Capillary  network  Fig.  434— Development  of capillaries  in  the  regenerating 
,  . .  tail  of  a  tadpole,    a,  b,  c,  d,  sprouts  and  cords  of 

extends    in    proportion    as  protoplasm  (Arnold). 

the  tail  increases  in  length 

and  breadth,  and  it,  at  the  same  time,  becomes  more  dense  by  the 
formation,  according  to  the  same  plan,  of  fresh  vessels  within  its 
meshes.  The  prolonga- 
tions by  which  the  vessels 
communicate  with  the 
star-shaped  cells,  consist 
at  first  of  narrow  pointed 
projections  from  the  side 
of  the  vessels,  which  gra- 
dually elongate  until  they 
come  in  contact  with  the 
radiated  processes  of  the 
cells.  The  thickness  of 
such  a  prolongation  often 
does  not  exceed  that  of  a 
fibril  of  fibrous  tissue,  and 
at  first  it  is  perfectly 
solid ;     but,    by    degrees, 

especially  after  its  junction  with  a  cell,  or  with  another  pro- 
longation, or  with  a  vessel  already  permeable  to  blood,  it  enlarges, 
and  a  cavity  then  forms  in  its  interior  (see  figs.  434,  435).     This 

3  e  2 


Fig.  435. — The  same  region  after  the  lapse  of  24  hours. 
The  "sprouts  and  cords  of  protoplasm"  have 
become  channelled  out  into  capillaries  (Arnold) . 


;SS 


GENERATION    AND    DEVELOPMENT. 


[chap.  XX. 


tissue  is  well  calculated  to   illustrate   the  various  steps   in   the 
development  of  blood-vessels  from  elongating  and  branching  cells. 


- — Captilc  humour  of  a  fatal  calf.    Two  vessels  are  seen  con- 

nected by  a    "cord"  of  protoplasm,   and  clothed  with  an  adventitia,   containing 
numerous  nuclei,    a,  insertion  of  this  "  cord  "  into  the  primary  walls  of  the  ve— 

Frey. 

In  many  cases  a  whole  network  of  capillaries  is  developed  from 
a  network  of  branched,  embryonic  connective-tissue  corpuscles  by 
the  joining  of  their  processes,  the  multiplication  of  their  nuclei, 
and  the  vacuolation  of  the  cell-substance.     The  vacuoles  gradually 

coalesce  till  all  the  partitions 
are  broken  down  and  the 
originally  solid  protoplasmic 
cell-substance  is.  so  to  speak, 
tunnelled  out  into  a  number 
of  tubes. 

Capillaries  may  also  be  de- 
veloped from  cells  which  are 
originally  spheroidal,  vacuoles 
form    in   the  interior  of  the 
cells  gradually  becoming  uni- 
ted by  fine  protoplasmic  pro- 
cesses :   by  the   extension  of 
the  vacuoles  into  them,  capil- 
lary    tubes     are     gradually 
formed. 
Morphology.     Heart. — When  it  first  appears,  the  heart  is  ap- 
proximately tubular    in  form.      It  receives    at   its   two   posterior 
angles  the  two  omphalo-inesenteric  veins,  and  gives  off  anteriorly 
the  primitive  aorta  (fig.  437). 


Pig.  437. — Fatal  heart  de- 

velopment. 1,  venous  extremity ;  2,  arterial 
extremity:  5 .  3 .  pulmonary  branches  ;  4, 
ductus  arteriosus.      Dalton.) 


QHAP.  xx.]  DEVELOPMENT  OF   EEABT.  789 

It  soon,  however,  becomes  curved  somewhat  in  the  shape 
horse-shoe,  with  the  convexity  towards  the  right,  the  venous  end 
being  at  the  same  rime   drawn  up  towards  the  head,  bo  that  it 


Fig.  438. — Heart  of  th*  Met  ,  6jj<A,  -md  85th  hours  of  incubation.    1,  the  venous 

trunks;  2,  the  auricle ;  3,  the  ventricle ;  4,  the  bulhus  arteriosus.     (Allen  Thomson. 

finally  lies  behind  and  somewhat  to  the  right  of  the  arterial.  It 
also  becomes  partly  divided  by  constrictions  into  three  cavities. 

Of  these  three  cavities  which  are  developed  in  all  Vertebrata, 
that  at  the  venous  end  is  the  simple  auricle,  that  at  the  arterial 
end  the  bulbous  arteriosus,  and  the  middle  one  is  the  simple 
ventricle. 

These  three  parts  of  the  heart  contract  in  succession.  The 
auricle  and  the  bulbus  arteriosus  at  this  period  lie  at  the  ex- 
tremities of  the  horse-shoe.  The  bulging  out  of  the  middle  portion 
inferiorly  gives  the  first  indication  of  the  future  form  of  the 
ventricle  (fig.  438).  The  great  curvature  of  the  horse-shoe  by  the 
same  means  becomes  much  more  developed  than  the  smaller  curva- 
ture between  the  auricle  and  bulbus  ;  and  the  two  extremities,  the 
auricle  and  bulb,  approach  each  other  superiorly,  so  as  to  produce 
a  greater  resemblance  to  the  later  form  of  the  heart,  whilst  the 
ventricle  becomes  more  and  more  developed  inferiorly.  The 
heart  of  Fishes  retains  these  three  cavities,  no  further  division  by 
internal  septa  into  right  and  left  chambers  taking  place.  In 
Amphibia,  also,  the  heart  throughout  life  consists  of  the  three 
muscular  divisions  which  are  so  early  formed  in  the  embrvu  ;  but 
the  auricle  is  divided  internally  by  a  septum  into  a  pulmonary  and 
systeinie  auricle.  In  Reptiles,  not  merely  the  auricle  is  thus 
divided  into  two  cavities,  but  a  similar  septum  is  more  or  Less 
developed  in  the  ventricle.  In  Birds  and  Mammals,  both  auricle 
and  ventricle  undergo  complete  division  by  septa  :  whilst  in  these 
animals  as  well  as  in  reptiles,  the  bulbus  aorta?  is  not  permanent, 
but  becomes  lost  in  the  ventricles.  The  septum  dividing  the 
ventricle  commences  at  the  apex  and  extends  upwards.  The  sub- 
division of  the  auricles  is  very  early  foreshadowed  by  the  outgrowth 


790  GENERATION    AND    DEVELOPMENT.  [chap.  xx. 

of  the  two  auricular  appendages,  which  occurs  before  any  septum  is 
formed  externally.  The  septum  of  the  auricles  is  developed  from 
a  semilunar  fold,  which  extends  from  above  downwards.  In  man, 
the  septum  between  the  ventricles,  according  to  Meckel,  begins  to 
be  formed  about  the  fourth  week,  and  at  the  end  of  eight  weeks  is 
complete.  The  septum  of  the  auricles,  in  man  and  all  animals 
which  possess  it,  remains  imperfect  throughout  fcetal  life.  When 
the  partition  of  the  auricles  is  first  commencing,  the  two  vena? 
cava?  have  different  relations  to  the  two  cavities.  The  superior 
cava  enters,  as  in  the  adult,  into  the  right  auricle  ;  but  the 
inferior  cava  is  so  placed  that  it  appears  to  enter  the  left  auricle, 
and  the  posterior  part  of  the  septum  of  the  auricles  is  formed  by 
the  Eustachian  valve,  which  extends  from  the  point  of  entrance  of 
the  inferior  cava.  Subsequently,  however,  the  septum,  growing 
from  the  anterior  wall  close  to  the  upper  end  of  the  ventricular 
septum,  becomes  directed  more  and  more  to  the  left  of  the  vena 
cava  inferior.  During  the  entire  period  of  foetal  life,  there  remains 
an  opening  in  the  septum,  which  the  valve  of  the  foramen  ovale, 
developed  in  the  third  month,  imperfectly  closes. 

Bulbus  Arteriosus. — The  bulbus  arteriosus  which  is  originally 
a  single  tube,  becomes  gradually  divided  into  two  by  the  growth 
of  an  internal  septum,  which  springs  from  the  posterior  wall,  and 
extends  forwards  towards  the  front  wall  and  downwards  towards 
the  ventricles.  This  partition  takes  a  somewhat  spiral  direction, 
so  that  the  two  tubes  (aorta  and  pulmonary  artery)  which  result 
from  its  completion,  do  not  run  side  by  side,  but  are  twisted  round 
each  other. 

As  the  septum  grows  down  towards  the  ventricles,  it  meets  and 
coalesces  with  the  upwardly  growing  ventricular  septum,  and  thus 
from  the  right  and  left  ventricles,  which  are  now  completely 
separate,  arise  respectively  the  pulmonary  artery  and  aorta,  which 
are  also  quite  distinct.  The  auriculo-ventricular  and  semilunar 
valves  are  formed  by  the  growth  of  folds  of  the  endocardium. 

At  its  first  appearance  the  heart  is  placed  just  beneath  the  head 
of  the  foetus,  and  is  very  large  relatively  to  the  whole  body  :  but 
with  the  growth  of  the  neck  it  becomes  further  and  further 
removed  from  the  head,  and  lodged  in  the  cavity  of  the  thorax. 

Up  to  a  certain  period  the  auricular  is  larger  than  the  ventri- 
cular division  of  the  heart ;  but  this  relation  is  gradually  reversed 


chap,  xx.]  DEVELOPMENT   OF  THE  AETEBIES. 


791 


a>  developmenl   proceeds.     Moreover,  all  through  festal  life,  the 

walls  of  the  right  ventricle  arc  of  very  much  the  same  thickness 
a<  those  of  the  left,  which  may  probably  be  explained  by  the  fad 
that  in  the  foetus  the  right  ventricle  has  to  propel  the  blood  from 
the  pulmonary  artery  into  the  aorta,  and  thence  into  the  placenta, 
while  in  the  adult  it  only  drives  the  blood  through  the  lungs. 

Arteries. — The  primitive  aorta  arises  from  the   bulbus   arte- 
riosus and  divides  into  two  branches  which  arch  backwards,  one  on 
ii  side  of  the  foregut  and  unite  again  behind  it,  and  in  front  of 
the  notochord  into  a  single  vessel. 

This   gives  off  the   two   omphalomesenteric   arteries,  which   distribute 
branches  all  over  the  yolk— ac  :  this  area  vaseulom  in  the  chick  attaining  , 
large  development,  and  being  limited  all  round  by  a  vessel  known  as  the 
sinus  terminal  is. 

The  blood  is  collected  by  the  venous  channels,  and  returned  through  the 
omphalo-mesenteric  veins  to  the  heart. 

Behind  this  pair  of  primitive  aortic  arches,  four  more  pairs  make 
their  appearance  successively,  so  that  there  are  five  pairs  in  all. 
each  one  running  along  one  of  the  visceral  arches. 

These  five  are  never  all  to  be  seen  at  once  in  the  embryo  of 
higher  animals,  for  the  two  anterior  pairs  gradually  disappear, 
while  the  posterior  ones  are  making  their  appearance,  so  that  at 
length  onlv  three  remain. 

In  Fishes,  however,  they  all  persist  throughout  life  as  the 
branchial  arteries  supplying  the  gills,  while  in  Amphibia  three 
pairs  persist  throughout  life. 

In  Reptiles,  Birds,  and  Mammals,  further  transformations 
occur. 

In  Reptiles  the  fourth  pair  remains  throughout  life  as  the 
permanent  right  and  left  aorta  ;  in  Birds  the  right  one  remains  as 
the  permanent  aorta,  curving  over  the  right  bronchus  instead  of 
the  left  as  in  Mammals. 

In  Mammals  the  left  fourth  aortic  arch  developes  into  the 
permanent  aorta,  the  right  one  remaining  as  the  subclavian  artery 
of  that  side.  Thus  the  subclavian  artery  on  the  right  side  corre- 
sponds to  the  aortic  arch  on  the  left,  and  this  homology  is  further 
confirmed  by  the  fact  that  the  recurrent  laryngeal  nerve  hooks 
under  the  subclavian  on  the  right  side,  and  the  aortic  arch  on  the 
left. 


;92 


GENERATION  AXD  DEVELOPMENT. 


[CHAP.   XX. 


The  third  aortic  arch  remains  as  the  external  carotid  artery, 
while  the  fifth  disappears  on  the  right  side,  but  on  the  left  forms 
the  pulmonary  artery.  The  distal  end  of  this  arch  originally  opens 
into  the  descending  aorta,  and  this  communication  (which  is  per- 


I"ig.  ^39.— Diagram  of  the  aortic  arches  in  a  mammal,  showing  transformations  which 
give  rise  to  the  permanent  arterial  vessels.  .1,  primitive  arterial  stem  or  aortic  bulb, 
now  divided  into  A,  the  ascending  part  of  the  aortic  arch,  and  p,  the  pulmonary ;  a  <i\ 
right  and  left  aortic  roots  ;  .1'.  descending' aorta  ;  1,  2,  3,  4,  5,  the  five  primitive  aortic 
or  branchial  arches  :  I,  II,  III,  IV,  the  four  branchial  clefts  which,  for  the  sake  of 
clearness,  have  been  omitted  on  the  right  side.  The  permanent  systemic  vessels  are 
deeply,  the  pulmonary  arteries,  lightly  shaded  ;  the  parts  of  the  primitive  arches  which 
are  transitory  are  simply  outlined  ;  c,  placed  between  the  permanent  common  carotid 
arteries ;  c  e,  external  carotid  arteries:  e  !,  internal  carotid  arteries;  s,  right  sub- 
clavian, rising  from  the  right  aortic  root  beyond  the  fifth  arch  ;  >■,  right  vertebral  from 
the  same,  opposite  the  fourth  arch  ;  v  s,  left  vertebral  and  subclavian  arteries  rising 
together  from  the  left,  or  permanent  aortic  root,  opposite  the  fourth  arch ;  p,  pul- 
monary arteries  rising  together  from  the  left  fifth  arch  ;  <l,  outer  or  back  part  of  left 
fifth  arch,  forming  ductus  arteriosus  :  p  n,  p  n  ,  right  and  left  pneumogastric  nerves, 
descending  in  front  of  aortic  arches,  with  their  recurrent  branches  represented  dia- 
grammatically  aa  |  hind,  to  illustrate  the  relations  of  these  nerves  respec- 

tively to  the  right   subclavian  artery   (4  ,  and  the  arch  of  the  aorta  and  ductus 
arteriosus  (d).     (Allen  Thomson,  after  Eathke.) 

manent  throughout  life  in  many  reptiles  on  both  sides  of  the  body) 
remains  throughout  fcetal  life  under  the  name  of  ductus  arteriosus  : 
the  branches  of  the  pulmonary  artery,  to  the  right  and  left  lung- 
are  very  small,  and  most  of  the  blood  which  is  forced  into  the 
pulmonary  artery  passes  through  the  wide  ductus  arteriosus  into 
the  descending  aorta.  All  these  points  will  become  clear  on 
reference  to  the  accompanying  diagram  (fig.  439). 

As  the  umbilical  vesicle   dwindles   in   size,  the  portion  of  the 
omphalomesenteric  arteries  outside  the  body  gradually  disappears, 


CHAP.  XX.] 


DEVELOPMENT   OF   THE   VEINS. 


793 


Fig.  440. — Diagram  of  young  embryo 
and  its  vessels,  showing1  course  of 
circulation  in  the  umbilical  vesicle  ; 
and  also  that  of  the  allantois  (near 
the  caudal  extremity), -which  is  just 
commencing' .     (Dalton . ) 


the  part  inside  the  body  remaining  as  the  mesenteric  arteries  (figs. 
44o,  44i). 

Meanwhile  with  the  growth  of  the 
allantois  two  new  arteries  (umbilical) 
appear,  and  rapidly  increase  in  size 
till  they  are  the  largest  branches  of 
the  aorta  :  they  are  given  off  from 
the  internal  iliac  arteries,  and  for  a 
long  time  are  considerably  larger 
than  the  external  iliacs  which  supply 
the  comparatively  small  hind-limbs. 

Veins. — The  chief  veins  in  the 
early  embryo  may  be  divided  into 
two  groups,  visceral  and  parietal : 
the  former  includes  the  omphalo- 
mesenteric and  umbilical,  the  latter 
the  jugular  and  cardinal  veins.  The 
former  may  be  first  considered. 

The  earliest  veins  to  appear  in 
the  foetus  are  the  omphalo-mesenteric  which  return  the  blood 
from  the  yolk-sac  to  the  developing  auricle.  As  soon  as  the 
placenta  with  its  umbilical 
veins  is  developed,  these 
unite  with  the  omphalo- 
mesenteric, and  thus  the 
blood  which  reaches  the 
auricle  comes  partly  from 
the  yolk-sac  and  partly 
from  the  placenta.  The 
right  omphalo-mesenteric 
and  the  right  umbilical 
vein  soon  disappear,  and 
the  united  left  omphalo- 
mesenteric and  umbilical 
veins  pass  through  the  de- 
veloping liver  on  the  way 
to  the  auricle.  Two  sets 
of  vessels  make  their  ap- 
pearance    in     connection 


Fig.  441. — Diagram  of  embryo  and  its  vessels  at  a  Inter 
stage,  showing  the  second  circulation.  The 
pharynx,  oesophagus,  and  intestinal  canal  have 
become  further  developed,  and  the  mesenteiie 
arteries  have  enlarged,  while  the  umbilical 
vesicle  and  its  vascular  branches  are  very  much 
reduced  in  size.  The  large  umbilical  arteries  are 
seen  passing  out  in  the  placenta.     (Dalton.) 


794 


GENERATION  AND  DEVELOPMENT. 


[<  HAP.    XX. 


-with  the  liver  (veme  hepaticse  advehentes,  and  revehentes),  both 
opening  into  the  united  omphalo-mesenteric  and  umbilical  veins, 
in  such  a  way  that  a  portion  of  the  venous  blood  traversing  the 
latter  is  diverted  into  the  developing  liver,  and,  having  passed 
thouirh  its  capillaries,  returns  to  the  umbilical  vein  through  the 


& 


Tig.  442. — j-  I  the  B,  d  c,  du 

Cuvier,  right  and  left  ;  .  :i:?ht  and  left  cardinal  veins  ;  o,  left  omphalo-mesenteric 
vein  :  0,  light  omphalo-mesenteric  vein,  almost  shrivelled  up :  •  .  ■■'.  umbilical  veins. 
of  "which  "  .  the  right  one,  has  almost  disappeared.  Between  the  vena-  cardinales  is 
seen  the  outline  of  the  rudimentary  liver,  with  its  vente  hepatic*  advehentes,  and 
revehentes :  //.  ductus  venosus  :  '',  hepatic  veins  :  e  i,  vena  cava  inferior :  P,  portal 
vein:  P'  P  .  vente  advehentes  ;  m,  mesenteric  veins.     ,Kollik 

venae  hepaticse  revehentes  at  a  point  nearer  the  heart  (see 
fig.  442).  The  .  portion  of  vein  between  the  afferent  and  efferent 
veins  of  the  liver  becomes  the  ductus  venosus.  The  vena?  hepaticse 
advehentes  become  the  right  and  left  branches  of  the  portal  vein, 
the  venae  hepaticse  revehentes  become  the  hepatic  veins,  which  open 
just  at  the  junction  of  the  ductus  venosus  with  another  large 
vein  (vena  cava  inferior),  which  is  now  being  developed.  The 
mesenteric  portion  of  the  omphalo-mesenteric  vein  returning  blood 
from  the  developing  intestines  remains  as  the  mesenteric  vein, 
which,  by  its  union  with  the  splenic  vein  forms  the  portal. 

Thus  the  fcetal  liver  is  supplied  with  venous  blood  from  two 
sources,  through  the  umbilical  and  portal  vein  respectively.  At 
birth  the  circulation  through  the  umbilical  vein  of  course  com- 
pletelv  ceases  and  the  vessel  begins  at  once  to  dwindle,  so  that 
now  the  only  venous  supply  of  the  liver  is  through  the  portal 
vein.  The  earliest  appearance  of  the  parietal  system  of  veins  is 
the  formation  of  two  short  transverse  veins  (ducts  of  Cuvier) 
opening  into  the  auricle  on  either  side,  which  result  from  the 
union  of  a  jugular  vein,  collecting  blood  from  the  head  and  neck, 


HAP.    XX. 


DEVELOPMENT   OF   'I  EE   VEINS. 


795 


and  a  cardinal  vein  which  returns  the  blood  from  the  Wolffian 
'•'dies,  the  vertebral  column,  and  the  parieties  of  the  trunk.  This 
arrangement  persists  throughout  life  in  Fishes,  but  in  Mammals 
the  following  transformations  occur. 

A.S  the  kidneys  are  developing  a  new  vein  appears  (vena  cava 
inferior),  formed  by  the  junction  of  their  efferent  veins.  It  receives 
branches  from  the  legs  (iliac)  and  increases  rapidly  in  size  as 
they  grow  :  further  up  it  receives  the  hepatic  veins.  The  heart 
gradually  descends  into  the  thorax  causing  the  ducts  of  Cuvier  to 
become  oblique  instead  of  transverse.  As  the  fore-limbs  develop, 
the  subclavian  veins  are  formed. 

A  transverse  communicating  trunk  now  unites  the  two  ducts 

ABC  D 


de 


m 


Fig.  443. — Diagrams  illustrating  the  development  of  the  great  veins,  d  c,  ducts  of  Cuvier; 
/,  jugular  veins  ;  h,  hepatic  veins  ;  e,  cardinal  veins  ;  .?,  subclavian  vein  ;  j  i,  internal 
jugular  vein  ;  .;'  e,  external  jugiilar  vein  ;  a  z,  azygos  vein  ;  c  t,  inferior  vena  cava ;  r, 
renal  veins  ;  i  I,  iliac  veins  ;  h  i  j,  hypogastric  veins.     (Gegenbaur.) 

of  Cuvier,  and  gradually  increases,  while  the  left  duct  of  Cuvier 
becomes  almost-  entirely  obliterated  (all  its  blood  passing  by  the 
communicating  trunk  to  the  right  side)  (fig.  443,  c,  d).  The  right 
duct  of  Cuvier  remains  as  the  right  innominate  vein,  while  the 
communicating  branch  forms  the  left  innominate.  The  remnant 
of  the  left  duct  of  Cuvier  generally  remains  as  a  fibrous  band, 
running  obliquely  down  to  the  coronary  vein,  which  is  really  the 
proximal  part  of  the  left  duct  of  Cuvier.     In  front  of  the  root  of 


796  GENERATION    AND    DEVELOPMENT.  [chap,  xx, 

the  left  lung,  another  relic  may  be  found  in  the  form  of  the  so- 
called  vestigial  fold  of  Marshall,  which  is  a  fold  of  pericardium 
running  in  the  same  direction. 

In  many  of  the  lower  mammals,  such  as  the  rat,  the  left  ductus  Cuvieri 
remains  as  a  left  superior  cava. 

Meanwhile,  a  transverse  branch  carries  across  most  of  the  blood 
of  the  left  cardinal  vein  into  the  right;  and  by  this  union  the  great 
azygos  vein  is  formed. 

The  upper  portions  of  the  left  cardinal  vein  remain  as  the  left 
superior  intercostal  and  vena  azygos  minor  (fig.  443,  d). 

Circulation  of  Blood  in  the  Foetus. 

The  circulation  of  blood  in  the  foetus  differs  considerably  from 
that  of  the  adult.  It  will  be  well,  perhaps,  to  begin  its  description 
by  tracing  the  course  of  the  blood,  which,  after  being  carried  out 
to  the  placenta  by  the  two  umbilical  arteries,  has  returned,  cleansed 
and  replenished,  to  the  foetus  by  the  umbilical  vein. 

It  is  at  first  conveyed  to  the  under  surface  of  the  liver,  and 
there  the  stream  is  divided, — a  part  of  the  blood  passing  straight 
on  to  the  inferior  vena  cava,  through  a  venous  canal  called  the 
ductus  venosus,  while  the  remainder  passes  into  the  portal  vein, 
and  reaches  the  inferior  vena  cava  only  after  circulating  through 
the  liver.  Whether,  however,  by  the  direct  route  through  the 
ductus  venosus  or  by  the  roundabout  way  through  the  liver, — all 
the  blood  which  is  returned  from  the  placenta  by  the  umbilical 
vein  reaches  the  inferior  vena  cava  at  last,  and  is  carried  by  it 
to  the  right  auricle  of  the  heart,  into  which  cavity  is  also  pouring 
the  blood  that  has  circulated  in  the  head  and  neck  and  arms, 
and  has  been  brought  to  the  auricle  by  the  superior  vena  cava.  It 
might  be  naturally  expected  that  the  two  streams  of  blood  would 
be  mingled  in  the  right  auricle,  but  such  is  not  the  case,  or  only  to 
a  slight  extent.  The  blood  from  the  superior  vena  cava, — the  less 
pure  fluid  of  the  two — passes  almost  exclusively  into  the  right 
ventricle,  through  the  auriculo-ventricular  opening,  just  as  it  does 
in  the  adult ;  while  the  blood  of  the  inferior  vena  cava  is  directed 
by  a  fold  of  the  lining  membrane  of  the  heart,  called  the  Eusta- 
chian valve,  through  the  foramen  ovale  into  the  left  auricle,  whence 
it  passes  into  the  left  ventricle,  and  out  of  this  into  the  aorta,  and 


OHAP.   XX.  ] 


THE   FCETAL  CIRCULATION. 


797 


thence  to  all  the  body.  The  blood  of  the  superior  vena  cava, 
which,  as  before  said,  passes  into  the  right  ventricle,  is  sent  out 
thence  in  small  amount  through  the  pulmonary  artery  to  the  lungs, 


Jt.Com. Carotid  - 

1        L.CoThCurohu. 


K  Subclotv 


3i\wi  L$ulc2aP 


SuJier-tCT  Vena.  Cavoi 


R. Auricle — *£  ~* 


'  pDuctArt. 


IT!  J \LAv-ridl 


i  VentricU 
\Right 
'  '''Ventricle 


Vmbilical    I 
Veil* 


M  .--Aorta 

lit  k 


Right  Lobe. 


A—Aortct 


UmbiU.Cus-\ 


Artertf       \ 


IfvibiUccU 
Cord  ' 


\r\y.CIli«c 


\\— Ext Iliac 


Fig.  444.— Diagram  of  the  Fatal  Circulation. 

and  thence  to  the  left  auricle,  as  in  the  adult.  The  greater  part, 
however,  by  far,  does  not  go  to  the  lungs,  but  instead,  passes 
through  a  canal,  the  ductus  arteriosus,  leading  from  the  pulmonary 
artery  into  the  aorta  just  below  the  origin  of  the  three   great 


798  GENERATION    AND    DEVELOPMENT.  [chap.  xx. 

vessels  which  supply  the  upper  parts  of  the  body  ;  aud  there 
meeting  that  part  of  the  blood  of  the  inferior  vena  cava  which  has 
not  gone  into  these  large  vessels,  it  is  distributed  with  it  to  the 
trunk  and  lower  parts, — a  portion  passing  out  by  way  of  the  two 
umbilical  arteries  to  the  placenta.  From  the  placenta  it  is  re- 
turned by  the  umbilical  vein  to  the  under  surface  of  the  liver, 
from  which  the  description  started. 

Changes  after  Birth. — After  birth  the  foramen  ovale  closes, 
and  so  do  the  ductus  arteriosus  and  ductus  venosus,  as  well  as 
the  umbilical  vessels ;  so  that  the  two  streams  of  blood  which 
arrive  at  the  right  auricle  by  the  superior  and  inferior  vena  cava 
respectively,  thenceforth  mingle  in  this  cavity  of  the  heart,  and 
passing  into  the  right  ventricle,  go  by  way  of  the  pulmonary 
artery  to  the  lungs,  and  through  these,  after  purification,  to  the 
left  auricle  and  ventricle,  to  be  distributed  over  the  body.  (See 
Chapter  on  Circulation.) 


Development  of  the  Nervous  System. 

Nerves. — All  the  spinal  nerves  are  derived  from  the  meso- 
blast ;  also  all  the  cranial  nerves,  except  the  optic  and  olfactory, 
which  are  outgrowths  of  the  anterior  cerebral  vesicles.  From  the 
same  middle  layer  of  the  embryo  are  also  derived  the  ganglia  con- 
nected with  these  nerves,  and  the  whole  sympathetic  system  of 
nerves  and  ganglia. 

Spinal  Cord. — Both  the  brain  and  spinal  cord  have  a  different 
origin  from  that  of  the  nerves  which  arise  from  them.  These 
nerve-centres  are  developed  entirely  from  the  epiblast  (possibly, 
however,  a  portion  of  the  spinal  cord  originates  in  the  meso- 
blast);  while  the  nerves,  as  we  have  seen,  are  formed  from 
mesoblast.  The  spinal  cord  is  developed  out  of  the  primitive 
medullary  tube  which  results  from  the  folding  in  of  the  dorsal 
laminae  (m,  fig.  411). 

Soon  after  it  has  closed  in,  this  tube  is  found  to  be  somewhat 
oval  in  section,  with  a  central,  canal,  which,  in  sections,  presents 
the  appearance  of  an  elongated  slit,  slightly  expanded  at  each  end. 
The  two  opposite  sides  unite  (fig.  445)  in  the  centre  of  the  slit 
dividing  it  into  an  anterior  portion  (the  permanent  central  canal 
of  the  cord)  and  a  posterior,  which  makes  its  way  to  the  free 


chap,  xx.]      DEVELOPMENT   OF  THE   SPINAL  CORD. 


799 


surface,  and  persists  as  the  posterior  fissure  of  the  cord,  lodging  a 
wry  fine  process  of  pia  mater. 

At  this  period  the  cord  consists  almost  entirely  of  grey  matter, 
but  the  white  matter,  which  is  derived  probably  from  the  sur- 
rounding mesoblast,  becomes  deposited  around  it  on  all  sides, 
growing  up  especially  on  the  anterior  surface  of  the  cord  into 
the  two    anterior  columns.      These   are    separated   by  a    fissure 


Pig.  445. — Diagram  of  development  of  spinal  cord  :  ee,  central  canal :  af,  anterior  fissure  ; 
pf,  posterior  fissure;  g,  grey  matter;  w,  white  matter.     For  further  explanation  see 


(anterior  fissure  of  cord),  which  of  course  deepens  as  the  columns 
bounding  it  become  more  prominent  (fig.  445). 

By  the  development  of  various  commissures,  the  cord  is  com- 
pleted. 

When  it  first  appears,  the  spinal  cord  occupies  the  whole 
length  of  the  medullary  canal,  but  as  development  proceeds,  the 
spinal  column  grows  more  rapidly  than  the  contained  cord,  so 
that  the  latter  appears  as  if  drawn  up  till,  at  birth,  it  is 
opposite  the  third  lumbar  vertebra,  and  in  the  adult  opposite  the 
first  lumbar.  In  the  same  way  the  increasing  obliquity  of  the 
spinal  nerves  in  the  neural  canal,  as  we  approach  the  lumbar 
region,  and  the  " cauda  equina"  at  the  lower  end  of  the  cord,  are 
accounted  for. 

Brain. — We  have  seen  (p.  763)  that  the  front  portion  of  the 
medullary  canal  is  almost  from  the  first  widened  out  and  divided 
into  three  vesicles.  From  the  anterior  vesicle  (thalamence- 
phalon)  the  two  primary  optic  vesicles  are  budded  off  laterally  : 
their  further  history  will  be  traced  in  the  next  section.  Some- 
what later,  from  the  same  vesicle  the  rudiments  of  the  hemi- 
spheres appear  in  the  form  of  two  outgrowths  at  a  higher 
level,  which  grow  upwards  and  backwards.  These  form  the 
prosencephalon . 

In  the  walls  of  the  posterior  (third)  cerebral  vesicle,  a  thicken- 


Soo 


GENERATION  AXD  DEVELOPMENT.    [..hap.  xx. 


ing  appears  (rudimentary  cerebellum)  which  becomes   separated 
from  the  rest  of  the  vesicle  by  a  deep  inflection. 

At  this  time  there  are  two  chief  curvatures  of  the  brain  (fig. 
446,  3).  (1.)  A  sharp  bend  of  the  whole  cerebral  mass  down- 
wards round  the  end  of  the  notochord,  by  which  the  anterior 
vesicle,  which  was  the  highest  of  the  three,  is  bent  downwards, 
and  the  middle  one  comes  to  occupy  the  highest  position.     (2.) 


A       4, 


m  i/y\,ti 

[  t    /  5 

i 

r    / 

::;  ■jl 

■ : '] 

■/ 

•  yi— 

-■) 

f  I 


Pig.  44c. —  E  ss  in  development  of  human  brain    {magnified),     i.   2,  3,  are  from  an 

"  embryo  about  seven  weeks  old  :  4,  about  three  months  old.  m,  middle  cerebral  vesicle 
(mesencephalon)  ;  c,  cerebellum ;  m  o,  medulla  oblongata  ;  i,  thalameneephalon  ;  h, 
hemispheres  :  f ,  inf  undibulum  :  Fig.  3  shows  the  several  curves  which  occur  in  the  course 
of  development ;  Fig.  4  is  a  lateral  view,  showing  the  great  enlargement  of  the  cerebral 
hemispheres  which  have  covered  in  the  thalami,  leaving  the  optic  lobes,  m,  uncovered. 
KoUiker.) 

X.B. — In  fig.  2  the  line  i  terminates  in  the  right  hemisphere,  it  ought  to  be  continued 
into  the  thalameneephalon. 


A  sharp  bend,  with  the  convexity  forwards,  which  runs  in  from 
behind  beneath  the  rudimentary  cerebellum  separating  it  from  the 
medulla. 

Thus,  five  fundamental  parts  of  the  foetal  brain  may  be  distin- 
guished, which,  together  with  the  parts  developed  from  them  may 
be  presented  in  the  following  tabular  view. 


CHAP.  XX.  J 


DEVELOPMENT    OF    THE    BRAIN, 


8oi 


Table    of    Parts    Developed    from    Fundamental    Parts 

of    Brain. 


I.  Anterior 
Primary 

Vesicle. 


II  Middle 
Primary 

Vehicle. 

III.  Posterior 
Primary 

Vesicle. 


t  r.  Prosencephalon. 


Thalamencephalic 
(Diencephalon). 

Mesencephalon. 

Epcncephalon. 
Metencephalon. 


1  bfal  hemispheres,  corpora 
Btriata,  corpus  callosum,  fornix, 
lateral  ventricles,  olfactory  bulb 
(  Rhinencephalon). 

Thalami  optici,  pineal  gland,  pitui- 
tary body,  third  ventricle,  optic 
nerve  (primarily). 
Corpora  quadrigemina.  crura  cere- 
bri, aqueduct   of   Sylvius,  optic 
nerve  (secondarily), 
f  Cerebellum,  pons  Varolii,  anterior 
l      part  of  fourth  ventricle. 
(Medulla  oblongata,  fourth  ventri- 
~(     cle,  auditory  nerve. 

(Quaiii's  Anatomy.") 


The  cerebral  hemispheres  grow  rapidly  upwards  and  back- 
wards, while  from  their  inferior  surface  the  olfactory  bulbs  are 
budded  oft',  and  the  thalamencephalon,  from  which  they  spring, 
remains  to  form  the  third 
ventricle  and  optic  thalami. 
The  middle  cerebral  vesicle 
(mesencephalon)  for  some 
time  is  the  most  prominent 
part  of  the  fcetal  brain,  and 
in  Fishes,  Amphibia,  and 
Reptiles,  it  remains  unco- 
vered through  life  as  the 
optic  lobes.  But  in  Birds 
the  growth  of  the  cerebral 
hemispheres  thrusts  the 
optic  lobes  down  laterally, 
and  in  Mammalia  com- 
pletely overlaps  them.' 

In  the  lower  Mammalia  the  backward  growth  of  the  hemi- 
spheres ceases  as  it  were,  but  in  the  higher  groups,  such  as  the 
monkeys  and  man,  they  grow  still  further  back,  until  they  com- 
pletely cover  in  the  cerebellum,  so  that  on  looking  down  on  the 
brain  from  above,  the  cerebellum  is  quite  concealed  from  view. 
The  surface  of  the  hemispheres  is  at  first  quite  smooth,  but  as 

3  f 


Fig-.  447 


8ide  >>ew  of  foetolhrain  at  six  months, 
showing  commencement  of  formation  of  the 
principal  fissures  and  convolutions.  F, 
frontal  lobe  ;  P,  parietal ;  0,  occipital ; 
T,  temporal ;  a  a  a,  commencing  frontal 
convolutions  ;  s,  Sylvian  fissure  ;  s,  its  an- 
terior division  ;  c,  within  it  the  central  lobe 
or  island  of  Beil ;  r,  fissure  of  Rolando  ; 
P,  perpendicular  fissure.     (E.  Wagner.) 


802 


GENERATION  AND  DEVELOPMENT. 


[chav.  xx. 


early  as  the  third  month  the  great  Sylvian  fissure  begins  to  be 

formed  (fig.  446,  4). 

The  next    to  appear   is  the  parietooccipital    or  perpendicular 

fissure ;  these  two  great  fissures,  unlike 
the  rest  of  the  sulci,  are  formed  by  a 
curving  round  of  the  whole  cerebral 
mass. 

In  the  sixth  month  the  fissure  of 
Rolando  appears  :  from  this  time  till 
the  end  of  foetal  life  the  brain  grows 
rapidly  in  size,  and  the  convolutions 
appear  in  quick  succession ;  first  the 
great  primary  ones  are  sketched  out, 
then  the  secondary,  and  lastly  the  ter- 
tiary ones  in  the  sides  of  the  fissures. 
The  commissures  of  the  brain  (anterior, 
middle,  and  posterior),  and  the  corpus 
callosum,  are  developed  by  the  growth 
of  fibres  across  the  middle  line. 

The  Hippocampus  major  is  formed 
by  the  folding  in  of  the  grey  matter 
from  the  exterior  into  the  latter  ven- 
tricles. The  essential  points  in  the 
structure  and  arrangement  of  the  vari- 
ous parts  of  the  brain,  are  diagram- 
matically  shown  in  the  two  accom- 
panying figures  (figs.  448,  449). 


Mb 


Mo ' 


Fig.  448. — Diagrammatic  horizon- 
tal section  of  atVertebrate  brain. 
The  figures  serve  both  for  this 
and  the  next  diagram.  Mb, 
mid  brain  :  what  lies  in  front 
of  this  is  the  fore-,  and,  what 
lies  behind,  the  hind-brain ; 
Lt,  lamina  temiinalis  ;  Olf,  ol- 
factory lobes ;  Hmp,  hemi- 
spheres ;  Th.E,  thalamenceph- 
alon ;  Pn,  pineal  gland;  Py, 
pituitary  body  ;  F3I,  foramen 
of  Munro  ;  cs,  corpus  striatum ; 
Th,  optic  thalamus  ;  CO,  crura 
cerebri :  the  mass  lying  above 
the  canal  represents  the  cor- 
pora quadrigemina ;  Cb,  cere- 
bellum ;  I—  IX.,  the  nine  pairs 
of  cranial  nerves  ;  i,  olfactory 
ventricle ;  2,  lateral  ventricle  ; 
3,  third  ventricle ;  4,  fourth 
ventricle ;  + ,  iter  a  tertio  ad 
quartum  ventriculum. 

(Huxley.) 


Development  of  the  Organs  of 
Sense. 


Eye. — Soon   after    the    first    three 

cerebral  vesicles  have  become  distinct 

from  each  other,  the  anterior  one  sends 

out    a   lateral  vesicle  from  each  side, 

(primary    optic   vesicle),    which   grows 

out  towards  the  free  surface,  its  cavity  of  course  communicating 

with  that  of  the  cerebral  vesicle  through  the  canal  in  its  pedicle. 

It  is  soon  met  and  invaginated  by  an  in-growing  process  from  the 


CHAP.  XX.  ] 


DEVELOPMENT    OF    THE    EYE. 


803 


epiblast  (fig.  450),  wry  much  as  the  growing  tooth  is  met  by  the 
process  of  epithelium  which  produces  the  enamel  organ.     This 


IX   v 


Fig.  449. — Longitudinal  and  vertical  diagrammatic  section  of  a  Vertebrate  brain.  Letters 
as  before.  Lamina  terminalis  is  represented  by  the  strong  black  line  joining  Pa  and 
Py.     (Huxley.) 

process  of  the  epiblast  is  at  first  a  depression  which  ultimately 
becomes  closed  in  at  the  edges  so  as  to  produce  a  hollow  ball,  which 
is  thus  completely  severed  from  the  epithelium  with  which  it  was 

.1 


Fig.  450. — Longitudinal  section  of  tit  primary  opt:,-  vesicle  in  the  chick  magnified  (from 
Eemak). — A,  from  an  embryo  of  sixty-five  hours ;  B,  a  few  hours  later;  C,  of  the 
fourth  day  ;  c,  the  corneous  iayer  or  epidermis,  presenting  in  A,  the  open  depression 
for  the  lens,  which  is  closed  in  B  and  C  ;  1,  the  lens  follicle  and  lens  ;  pr,  the  primary 
optic  vesicle  ;  in  A  and  B,  the  pedicle  is  shown ;  in  C,  the  section  being  to  the  side  of 
the  pedicle,  the  latter  is  not  shown  ;  v,  the  secondary  ocular  vesicle  and  vitreous 
humour. 

originally  continuous.  From  this  hollow  ball  the  crystalline 
lens  is  developed.  By  the  ingrowth  of  the  lens  the  anterior 
wall  of  the  primary  optic  vesicle  is  forced  back  nearly  into  contact 
with  the  posterior,  and  thus  the  primary  optic  vesicle  is  almost 
obliterated.  The  cells  in  the  anterior  wall  are  much  longer  than 
those  of  the  posterior  wall ;  from  the  former  the  retina  proper  is 
developed,  from  the  latter  the  retinal  pigment. 

The   cup-shaped   hollow  in  which  the    lens  is   now  lodged    is 

3  f  2 


804 


GENERATION  AND  DEVELOPMENT. 


[CHAP.  XX. 


termed  the  secondary  optic  vesicle  :  its  walls  grow  up  all  round , 
leaving,  however,  a  slit  at  the  lower  part. 

Choroidal    Fissure.— 

Through  this  slit  (fig.  452), 
often  termed  the  choroidal 
fissure,  a  process  of  mesoblast 
containing  numerous  blood- 
vessels projects,  and  occupies 
the  cavity  of  the  secondary 
optic  vesicle  behind  the  lens, 
filling  it  with  vitreous  humour 
and  furnishing  the  lens  capsule 
and  the  capsulo  -  pupillary 
membrane.       This  process  in 

Fig".  451. — Diagrammatic  sketch  nj  a  vertical  (on-  x 

gitudinal section  through  the  eyeball  of a  human      AJ;immals    projects,     not     Onlv 
fcetus  of  four  weeks.    The  section  is  a  little  to  r     o 

the  side,  so  as  to  avoid  passing  through  the     m£0    ^he    secondary  Optic  Vesi- 
ocular  cleft ;  c,  the  cuticle  where  it  becomes  J       L 

later  the  corneal  epithelium;    I,  the   lens;      cJe    ^ut    also   into    the    pedicle 
op,  optic  nerve  formed  by  the  pedicle  of  the  A 

primary  optic  vesicle  ;  vp,  primary  medullary     0f    the     primary    Optic    Vesicle 
cavity-  or  optic  vesicle  ;  p,  the  pigment  layer  x 

of    the  retina;    r,   the  inner  wall  forming     invaginating    it    for    SOme    dis- 
the  retina  proper ;  vs,  secondary'  optic  vesicle  ° 

containing    the    rudiment    of    the   vitreous     tance    from  beneath,  and  thus 
humour.     X  ioo.     (Kulliker.)  . 

carrying  up  the  arteria  cen- 
tralis retime  into  its  permanent 
position  in  the  centre  of  the  optic 
nerve. 

This  invagination  of  the  optic 
nerve  does  not  occur  in  birds,  and 
consequently  no  arteria  centralis 
retinas  exists  in  them.  But  they 
possess  an  important  permanent 
relic  of  the  original  protrusion  of 
the  mesoblast  through  the  choroidal 
fissure,  forming  the  pecten,  while  a 
remnant  of  the  same  fissure  some- 
times occurs  in  man  under  the  name 
coloboma  iridis.  The  cavity  of  the 
primary  optic  vesicle  becomes  com- 

mencmg  vitreous  humour  withm  V  e         n    ,    -,  lti«-»*»J       n-nA      +1-.^     t-r\r\a 

secondary  optic  vesicle;. '.the  ocular     pletely    obliterated,    and    tne    10QS 

clef t  through  which  the  loop  of  the  i         ^^  „-»«,«  ;,-.+^  o-r>v\r\oi+inr>  m'+V» 

central  blood-vessel, «,  projects  from      and  COlieS  COUie  mtO  appOSltlOll  WltU 


Fig.  452. —  Transverse  vertical  section  of 
the  eyeball  of  a  human  embryo  of  four 
weeks.  The  anterior  half  of  the  sec- 
tion is  represented  :  pr,  the  remains 
of  the  cavity  of  the  primary  optic 
vesicle  ;  .?>,  the  inner  part  of  the 
outer  layer  forming  the  retinal  pig- 
ment ;  /•,  the  thickened  inner  part 
giving  rise  to  the  columnar  and  other 
structures  of  the  retina  ;  v,  the  com- 
mencing vitreous  humour  within  t:  e 


below ;    1,  the  len 

cavity,     x  100.     (Kulliker.) 


the   pigment   layer  of   the    retina. 


<  BAP.   XX.  | 


DEVELOPMENT    OF    THE    EAR. 


805 


The  cavity  of  Its  pedicle  disappears  and  the  solid  optic  nerve  is 
formed  Meanwhile  the  cavity  which  existed  in  the  centre  of  the 
primitive  lens  becomes  filled  up  by  the  growth  of  fibres  from  its 
posterior  wall.     The  epithelium   of  the  cornea  is  developed  from 

the  epiblast,  while  the  corneal   tissue  proper  is  derived  from  the 
•blast  which  intervenes  between  the  epiblasl  and  the  primitive 
lens  which  was  originally  continuous  with  it.     The  sclerotic  coat 
is    developed    round    the 
eye-ball  from  the  general 
mesoblast  in  which    it   is 
imbedded. 

The  iris  is  formed  rather 
late,  as  a  circular  septum 
projecting  inwards,  from 
the  fore  part  of  the  cho- 
roid, between  the  lens  and 
the  cornea.  In  the  eye  of 
the  foetus  of  Mammalia, 
the  pupil  is  closed  by  a 
delicate  membrane,  the 
an  mbrana  pupillariSfYrhich 
forms  the  front  portion  of 
a  highly  vascular  mem- 
brane that,  in  the  foetus, 
surrounds  the  lens,  and  is 
named  the  membrana  capsulo-pupUlarig  (fig.  453).  It  is  supplied 
with  blood  by  a  branch  of  the  arteria  centralis  retina-,  which, 
passing  forwards  to  the  back  of  the  lens,  there  subdivides.  The 
membrana  capsulo-pupillaris  withers  and  disappears  in  the  human 
subject  a  short  time  before  birth. 

The  eyelids  of  the  human  subject  and  mammiferous  animals 
like  those  of  birds,  arc  first  developed  in  the  form  of  a  ring. 
They  then  extend  over  the  globe  of  the  eye  until  they  meet  and 
become  firmly  agglutinated  to  each  other.  But  before  birth,  or 
in  the  Carnivore  after  birth,  they  again  separate. 

Ear. — Very  early  in  the  development  of  the  embryo  a  depres- 
sion or  ingrowth  of  the  epiblast  occurs  on  each  side  of  the  head 
which  deepens  and  soon  becomes  a  closed  follicle.  This  primary 
otic  vesicle  which  closely  corresponds  in  its  formation  to  the  lens 


Fig.  453. — Blood-vessels  of  the  capsvio~pujnllary  mem- 
brane  of  a  new-bori\  kitten,  magnified.  The 
drawing  is  taken  from  a  preparation  injected 
by  Tierseh,  and  shows  in  the  central  part  the 
convergence  of  the  net-work  of  vessels  in  the 
pupillary  membrane.     (Kolliker.) 


8o6  .      GENERATION    AND    DEVELOPMENT.  [chap.  xx. 

follicle  in  the  eye,  sinks  down  to  some  distance  froni  the  free 
surface ;  from  it  are  developed  the  epithelial  lining  of  the  mem- 
branous labyrinth  of  the  internal  ear,  consisting  of  the  vestibule 
and  its  semicircular  canals  and  the  scala  media  of  the  cochlea. 
The  surrounding  mesoblast  gives  rise  to  the  various  fibrous  bony 
and  cartilaginous  parts  which  complete  and  enclose  this  mem- 
branous labyrinth,  the  bony  semicircular  canals,  the  walls  of  the 
cochlea  with  its  scala  vestibuli  and  scala  tympani.  In  the 
mesoblast,  between  the  primary  otic  vesicle  and  the  brain,  the 
auditory  nerve  is  gradually  differentiated  and  forms  its  central 
and  peripheral  attachments  to  the  brain  and  internal  ear  respec- 
tively. According  to  some  authorities,  however,  it  is  said  to  take 
its  origin  from  and  grow  out  of  the  hind  brain. 

The  Eustachian  tube,  the  cavity  of  the  tympanum,  and  the 
external  auditory  passage,  are  remains  of  the  first  branchial  cleft. 
The  membrana  tympani  divides  the  cavity  of  this  cleft  into  an 
internal  space,  the  tympanum,  and  the  external  meatus.  The 
mucous  membrane  of  the  mouth,  which  is  prolonged  in  the  form 
of  a  diverticulum  through  the  Eustachian  tube  into  the  tympanum, 
and  the  external  cutaneous  system,  come  into  relation  with  each 
other  at  this  point ;  the  two  membranes  being  separated  only  by 
the  proper  membrane  of  the  tympanum. 

The  pinna  or  external  ear  is  developed  from  a  process  of 
integument  in  the  neighbourhood  of  the  first  and  second  visceral 
arches,  and  probably  corresponds  to  the  gill-cover  (operculum)  in 
fishes. 

Nose- — The  nose  originates  like  the  eye  and  ear  in  a  depres- 
sion of  the  superficial  epiblast  at  each  side  of  the  fronto-nasal 
process  (primary  olfactory  groove),  which  is  at  first  completely 
separated  from  the  cavity  of  the  mouth,  and  gradually  extends 
backwards  and  downwards  till  it  opens  into  the  mouth. 

The  outer  angles  of  the  fronto-nasal  process,  uniting  with  the 
maxillary  process  on  each  side,  convert  what  was  at  first  a  groove 
into  a  closed  canal. 

Development  of  the  Alimentary  Canal. 

The  alimentary  canal  in  the  earliest  stages  of  its  development 
consists  of  three  distinct  parts — the  fore  and  hind  gut  ending 
blindly  at  each  end  of  the  body,  and  a  middle  segment  which 


nitr.  xx.]     DEVELOPMENT    OF    All  M  KNT.MiV    OANAL. 


807 


oommunicatea  freely  on  its  ventral  surface'  with  the  cavity  of  the 
yelk-sac  through  the  vitelline  or  omphalo  mesenteric  duet  (p.  767) 
From  the  fore-gut  are  formed  the  pharynx,  oesophagus,  and 
stomach  ;  from  the  hind-gut*  the  lower  end  of  the  oolon  and  the 
rectum.  The  mouth  is  developed  l>y  an  involution  of  the  epiblast 
1  iet ween  the  maxillary  and  mandibular  processes,  which  becomes 

ABC  D 


Fig.  454. —  Outline*  of  the  form  and  position  of  the  alimentary  canal  m  successive  stages  of  its 
develop mnit.  A,  alimentary  canal,  kc,  in  an  embryo  of  four  weeks  ;  B,  at  six  weeks  ; 
C,  at  eight  weeks  ;  D,  at  ten  weeks  ;  1,  the  primitive  lungs  connected  with  the  pharynx  ; 
s,  the  stomach  ;  d,  the  duodenum ;  i,  the  small  intestine  ;  f ,  the  large  ;  c,  the  ceecum 
and  vermiform  appendage ;  r,  the  rectum ;  d,  in  A,  the  cloaca  ;  a,  in  B,  the  anus 
distinct  from  s  i,  the  sinus  uro-genitalis ;  v,  the  yelk-sac ;  v  i,  the  vitello-intestinal 
duct;  u,  the  urinary  bladder  and  urachus  leading  to  the  allantois;  g,  genital  ducts. 
(Allen  Thomson.) 

deeper  and  deeper  till  it  reaches  the  blind  end  of  the  fore-gut,  and 
at  length  communicates  freely  with  the  pharynx  by  the  absorption 
of  the  partition  between  the  two. 

At  the  other  end  of  the  alimentary  canal  the  anus  is  formed 
in  a  precisely  similar  way  by  an  involution  from  the  free  surface, 
which  at  length  opens  into  the  hind-gut.  When  the  depression 
from  the  free  surface  does  not  reach  the  intestine,  the  condition 
known  as  imperforate  anus  results.  A  similar  condition  may  exist 
at  the  other  end  of  the  alimentary  canal  from  the  failure  of  the 
involution  which  forms  the  mouth,  to  meet  the  fore-gut.  The 
middle  portion  of  the  digestive  canal  becomes  more  and  more 
closed  in  till  its  originally  wide  communication  with  the  yelk-sac 


So8 


GENERATION    AND    DEVELOPMENT.  [chap.  xx. 


Fig.  455. — First  appearance  of  the  parotid 
gland  in  the  embryo  of  a  sJit 


becomes  narrowed  down  to  a  small  duct  (vitelline).     This  duct 
usually    completely   disappears    in    the    adult,    but    occasionally 

the  proximal  portion  remains  as  a 
diverticulum  from  the  intestine. 
Sometimes  a  fibrous  cord  attaching 
some  part  of  the  intestine  to  the 
umbilicus,  remains  to  represent  the 
vitelline  duct.  Such  a  cord  has  been 
known  to  cause  in  after-life  strangu- 
lation of  the  bowel  and  death. 

The  alimentary  canal  lies  in  the 
form  of  a  straight  tube  close  beneath 
the  vertebral  column,  but  it  gradu- 
ally becomes  divided  into  its  special 
parts,  stomach,  small  intestine,  and 
large  intestine  (fig.  454),  and  at  the 
same  time  comes  to  be  suspended  in  the  abdominal  cavity  by 
means  of  a  lengthening  mesentery  formed  from  the  splanchno- 

pleure  which  attaches  it 
to  the  vertebral  column. 
The  stomach  originally 
has  the  same  direction  as 
the  rest  of  the  canal ;  its 
cardiac  extremity  being 
superior,  its  pyloms  infe- 
rior. The  changes  of  posi- 
tion which  the  alimentary 
canal  undergoes  may  be 
readily  gathered  from  the 
accompanying  figures  (fig. 

454;. 

Pancreas  and  Sali- 
vary Glands. — The  prin- 
cipal glands  in  connection 
with  the  intestinal  canal 
are  the  salivary,  pancreas, 
and  the  liver.  In  Mam- 
malia, each  salivary  gland  first  appeal's  as  a  simple  canal  with 
bud-like  processes  (fig.  455),  lying  in  a  gelatinous  nidus  or  blas- 


K 


■.  456.—  Lobules  of  the  parotid,  with  the  salivary 
ducts,  in  the  embryo  of  the  sheep,  at  a  more 
advanced  stage. 


<  HAP.  XX.] 


PKYKI.oi'MEXT    OF    THE    LIVER. 


809 

tenia,  and  eommunicating  with  the  cavity  of  the  mouth.  As  the 
development  of  the  gland  advances,  the  canal  becomes  more  and 
more  ramified,  increasing  at  the 
expense  of  the  blastema  in  which 
it  is  still  enclosed.  The  branches 
or  salivary  ducts  constitute  an  in- 
dependent system  of  closed  tubes 
(fig.  456).  The  pancreas  is  deve- 
loped exactly  as  the  salivary 
-lands,  but  is  developed  from  the 
hypoblast  lining  the  intestine, 
while  the  salivary  glands  are 
formed  from  the  epiblast  lining 
the  month. 

Liver. — The  liver  is  developed 
by  the  protrusion,  as  it  were,  of  a 
part  of  the  walls  of  the  intestinal 
canal,  in  the  form  of  two  conical 
hollow  branches  which  embrace  the 
common  venous  stem  (figs.  457, 
458).  The  outer  part  of  these 
cones  involves  the  omphalomesenteric  vein,  which  breaks  up  in  its 
interior  into  a  plexus  of  capillaries,  ending  in  venous  trunks  for 


Pig.  457. — Diagram  of  part  of  d 
tract  of  a  chick  (4th  day).  'The  black 
line  represents  hypoblast,  the  outer 
shading  mesoblast  :  >  g,  lung  diverti- 
cuhim,  with  expanded  end  forming 
primary  lung-vesicle;  S  t,  stomach  ; 
7,  two  hepatic  diverticula,  with  their 
terminations  united  by  sobd  rows  of 
hypoblast  cells;  p,  diverticulum  of 
the  pancreas  with  the  vesicular  diver- 
ticula coming  from  it.     (Gotte.) 


Fig.  458. — Btidimenta  of  the  liver  on  tl-  of  a  chick  at  the  fifth  day  of  incubation.     1. 

heart ;  2,  intestine  ;  3,  diverticulum  of  the  intestine  in  which  the  liver  (4)  is  developed  ; 
5,  part  of  the  mucous  layer  of  the  gernnnal  membrane.     (Midler.) 


the  conveyance  of  the  blood  to  the  heart.  The  inner  portion  of 
the  cones  consists  of  a  number  of  solid  cylindrical  masses  of  cells, 
derived  probably   from    the    hypoblast,    which    become  gradually 


Sio 


Ol^sEKATlUN  AND  DEVELOPMENT. 


[CHAP.   XX. 


hollowed  by  the  formation  of  the  hepatic  ducts,  and  among  which 
blood-vessels  are  rapidly  developed.  The  gland-cells  of  the  organs 
are  derived  from  the  hypoblast,  the  connective  tissue  and  vessels 
without  doubt  from  the  mesoblast.  The  gall-bladder  is  developed 
as  a  diverticuluni  from  the  hepatic  duct.  The  spleen,  lymphatic, 
and  thymus  glands  are  developed  from  the  mesoblast :  the  thyroid 
partly  also  from  the  hypoblast  which  grows  into  it  as  a  diverti- 
culum from  the  fore-gut. 


Development  of  the  Respiratory  Apparatus. 

The  lungs,  at  their  first  development,  appear  as  small  tubercles, 
or  diverticular  from  the  abdominal  surface  of  the  oesophagus. 

The   two  diverticula  at    first 
ji.  n  c  open  directly  into  the  oesopha- 

gus, but  as  they  grow,  a  separate 
tube  (the  future  trachea)  is 
formed  at  their  point  of  fusion, 
opening  into  the  oesophagus  on 
its  anterior  surface.  These  pri- 
mary diverticula  of  the  hypo- 
blast of  the  alimentary  canal 
send  off  secondary  branches  into 
the  surrounding  mesoblast,  and 
these  again  give  off  tertiary 
branches,  forming  the  air-cells. 
Thus  we  have  the  lungs  formed  : 
the  epithelium  lining  their  air 
cells,  bronchi,  and  trachea  being 
derived  from  the  hypoblast,  and 


Fig.  459   illustrates   Ou  of  the 

respiratory  orgeats.  A,  is  the  oesophagus 
of  a  chick  on  the  fourth  day  of  incuba- 
tion, with  the  rudiments  of  the  trachea 
on  the  lung  of  the  left  side,  viewed  late- 
rally ;  i ,  the  inferior  wall  of  the  oesopha- 
gus ;  2,  the  upper  wall  of  the  same  tube  ; 
3,  the  rudimentary  lung ;  4,  the  stomach. 
b,  is  the  same  object  seen  from  below, 
so  that  both  lungs  are  visible.  c,  shows 
the  tongue  and  respiratory  organs  of  the 
embiyo  of  a  horse  :  1,  the  tongue  ;  2,  the 
larynx ;  3,  the  trachea  ;  4,  the  lungs, 
viewed  from  the  upper  side.  [After 
Bathke.) 


all  the  rest  of  the  lung-tissue, 
nerves,  lymphatics,  and  blood-vessels,  cartilaginous  rings,  and 
muscular  fibres  of  the  bronchi  from  the  mesoblast  The  dia- 
phragm is  early  developed. 


The  Wolffian  Bodies,  Urinary  Apparatus,  and  Sexual 

Organs. 

The  Wolffian  bodies  are  organs  peculiar  to  the  embryonic  state, 


ohap.  xx.|  DEVELOPMENT  OF  OENITO-UBINART  APPARATUS.  8ll 

and  may  be  regarded  as  temporary,  rather  than  rudimentol,  kid- 
aeyH  :  for  although  they  seem  to  discharge  the  functions  of  these 
latter  organs,  they  are  not  developed  into  them. 

Appearance  of  first  rudiments.  The  Wolffian  duct  makes 
its  appearance  at  an  early  stage  in  the  history  of  the  embryo,  as  a 
oord  ruiining  longitudinally  on  each  side  in  the  mass  of  meso- 
blast,  which  lies  just  external  to  the  protovertebrsa  (ung,  fig. 
460).  This  eor»l,  at  first  solid,  becomes  gradually  hollowed  out 
to    form    a    tube  (Wolffian    duct)   which   sinks  down    till    it   pro- 


d'd 


Fig.  460. — Transverse  of  emhryo  chick  (third  clay),  m  r,  rudimentary  spinal  cord;  the 
primitive  central  canal  has  become  constricted  in]  the  middle  ;  c  h,  notochord ; 
uw  h,  primordial  vertebral  mass  ;  m,  muscle-plate  ;  rfr,  df,  hypoblast  and  visceral 
layer  of  mesoblast  lining  groove,  which  is  not  yet  closed  in  to  form  the  intestines ;  a  o, 
one  of  the  primitive  aortse  ;  »  «,  Wolffian  body ;  "  n  >/,  Wolffian  duct;  v  c,  vena  cardi- 
nalis ;  h,  epiblast ;  h  pf  somatopleui'e  and  its  reflection  to  form  af,  amniotic  fold ;  p, 
pleuroperitoneal  cavity.     (Kolliker.) 


jects    beneath    the    lining    membrane  into  the  pleuro-peritoneal 
cavity. 

The  primitive  tube  thus  formed  sends  off  secondary  diverticula 
at  frequent  intervals  which  grow  into  the  surrounding  mesoblast : 
tufts  of  vessels  grow  into  the  blind  ends  of  these  tubes,  invaginat- 
ing  them  and  producing  "  Malpighian  bodies "  very  similar  in 
appearance  to  those  of  the  permanent  kidney,  which  constitute 
the  substance  of  the  Wolffian  body.  Meanwhile  another  portion 
of  mesoblast  between  the  Wolffian  body  and  the  mesentery 
projects  in  the  form  of  a  ridge,  covered  on  its  free  surface  with 
epithelium  termed  "germ  epithelium."     From  this  projection  is 


8l2 


GENERATION    AXD    DEVELOPMENT.  [chap.  xx. 


developed  the  reproductive  gland  (ovary  or   testis   as  the    case 
may  be). 

Simultaneously,    on    the    outer    wall    of    the    Wolffian    body, 

between    it    and    the    body-wall    on    each    side,   an    involution  is 
f<  trmed  from  the  pleuro-peritoneal  cavity  in  the  form  of  a  longi- 

9 


Fig.  4fi. — fi  ...         thef<  irthday.     m,  mesentery;  Z,  somato- 

pleure  :  a '.  germinal  epithelium,  from  -which  z,  the  duct  of  M  tiller,  becomes  involuted  ; 
".thickened  part  of  germinal  epithelium  in  which  the  primitive  ova  C  and  o,  are 
lying  :  E,  modified  mesoblast,  which  will  form  the  stroma  of  the  ovary ;  W  A",  "Wolffian 
body;  #>  "Wolffian  duct ;   x  160.     ;Waldeyer.) 

tudinal  furrow,  whose  edges  soon  close  over  to  form  a  duct 
(Midlers  duct). 

All  the  above  points  are  shown  in  the  accompanying  figures, 
460,  461,  462,  463. 

The  "Wolffian  bodies,  or  temporary  kidneys,  as  they  may  be 
termed,  give  place  at  an  early  period  in  the  human  foetus  to  their 
successors,  the  perm" neat  kidneys,  which  are  developed  behind 
them.  They  diminish  rapidly  in  size,  and  by  the  end  of  the  third 
month  have  almost  entirely  disappeared.  In  connection,  however, 
with  their  upper  part,  in  the  male,  there  are  developed  from  a  new 
mass  of  blastema,  the  vasa  efferentia^  cord  vasculosis  and  globus  major 


«h\i\  xx.  I         DEVELOPMENT    OF    THE   EPIDIDYMIS. 


81 


of  the  epididymis  \  and  thus  is  brought  about  a  direct  connection 
between  the  secreting  pari  of  the  testicle  and  its  duct  (Cleland, 
Banks).  The  Wolffian  ducts  persist  in  the  male,  and  are  developed 
to  form  the  body  and  globus  minor  of  the  epididymis,  the  vas 


WW 


w.d     M 


Wrf      M 


'      t'.v 


Fig.  462. — Diagram  showing  the  relations  of  the  female  [the  left-hand  figure  9)  and  of  the  mule 
{the  right  hand  figure  &  )  reproductive  organs  to  the  general  plan  figure)  oj 

organs  in  tin  higher  vertebrata  (including  man).     C  I,  cloaca;    /.'.rectum;  B  J,  urinary 
bladder  ;   U,  ureter  ;  K,  kidney  ;   U  h,  urethra  ;   G,  genital  gland,  ovary  or  testis  ;    n\ 
"Wolffian  body  ;    Wd,  "Wolffian  duct ;  Mt  Miillerian  duct ;  P  s  t,  prostate  gland  ; 
Cowper's  gland  ;   C  sp,  carpus  spongiosum  ;   0  c,  corpus  cavemosum. 

In  the  female. — V,  vagina;   U  t,  uterus;  /•>,  Fallopian  tube  ;   G  t,  Gaertner's  duct;  Pv, 

parovarium  ;  A,  anus  ;   Oc,  Gap,  clitoris. 
Tntht   male.—C-sp,  Oc,  penis;   6"/,  uterus  masculinus  ;  V  s,  vesieula  seminalis  ;   V  d,  vas 

deferens .     ( Huxley . ) 


deferens,  and  ejaculatory  duct  on  each  side,  the  vesiculae  seminaleq 
forming  diverticula  from  their  lower  part.  In  the  female  a  small 
relic  of  the  Wolffian  body  persists  as  the  "parovarium;"  in  the 
male  a  similar  relic  is  termed  the  "organ  of  Giraldes."  The  lower 
end  of  the  Wolffian  duet  remains  in  the  female  as  the  "duct  of 
Gaertner"  which  descends  towards,  and  is  lost  upon,  the  anterior 
wall  of  the  vagina. 

From  the  lower  end  of  the  Wolffian  duct  a  diverticulum  grows 


814 


GENERATION  AND  DEVELOPMENT. 


[CHAP.  XX. 


back  along  the  body  of  the  embryo  towards  its  anterior  extremity, 
and  ultimately  forms  the  ureter.  Secondary  diverticula  are  given 
off  from  it  and  grow  into  the  surrounding  blastema  of  blood-vessels 
and  cells. 

Malpighian  bodies  are  formed  just  as  in  the  Wolffian  body,  by 
the  invagination  of  the  blind  knobbed  end  of  these  diverticula  by 
a  tuft  of  vessels  (fig.  463).  This  process  is  precisely  similar  to  the 
invagination  of  the  primary  optic  vesicle  by  the  rudimentary  lens. 

Thus  the  kidney  is  developed, 
consisting  at  first  of  a  number 
of  separate  lobules;  this  con- 
dition remaining  throughout 
life  in  many  of  the  lower  ani- 
mals, e.g.,  seals  and  whales, 
and  traces  of  this  lobulation 
being  visible  in  the  human 
foetus  .at  birth.  In  the  adult 
all  the  lobules  are  fused  into 
a  compact  solid  organ. 

The  supra-renal  capsules 
originate  in  a  mass  of  meso- 
blast  just  above  the  kidneys  ; 
soon  after  their  first  appear- 
ance they  are  very  much  larger 
than  the  kidneys  (see  fig. 
464),  but  by  the  more  rapid  growth  of  the  latter  this  relation  is 
soon  reversed. 

Later  Development. 

The  first  appearance  of  the  generative  gland  has  been  already 
described :  for  some  time  it  is  impossible  to  determine  whether  an 
ovary  or  testis  will  be  developed  from  it ;  gradually  however  the 
special  characters  belonging  to  one  of  them  appear,  and  in  either 
case  the  organ  soon  begins  to  assume  a  relatively  lower  position 
in  the  body ;  the  ovaries  being  ultimately  placed  in  the  pelvis ; 
while  towards  the  end  of  foetal  existence  the  testicles  descend  into 
the  scrotum,  the  testicle  entering  the  internal  inguinal  ring  in  the 
seventh  month  of  foetal  life,  and  completing  its  descent  through 
the  inguinal  canal  and  external  ring  into  the  scrotum  by  the  end 


Fig.  463. — Transverse  section  of  a  developing 
Malpighian  capsule  and  tuft  (human). 
From  a  fetus  at  about  the  fourth  month ; 
a,  flattened  cells  growing  to  form  the 
capsule  ;  b,  more  rounded  cells,  continu- 
ous with  the  above,  reflected  round  c,  and 
finally  enveloping  it ;  c,  mass  of  embry- 
onic cells  -which  will  later  become  deve- 
loped into  blood-vessels,      x  300.     ("W. 

Pye.) 


chap.  xx.]  DESCENT    OP    THE    TESTICLES.  S15 

of  the  eighth  month.  A  pouch  of  peritoneum,  theproA  1  rtnalis, 

preoedee  it  in  it-  descent,  and  ultimately  forms  the  tunica  vaginalis 
or  serous  covering  of  the  organ;  tlic  communication  between  the 
tunica  vaginalis  and  the  cavity  of  the  peritoneum  being  closed  only 

short  time  before  birth.  In  its  descent,  the  testicle  or  ovary  of 
course  retains  the  blood  .  nerv<  b,  and  lymphatics,  which 

were  supplied  to  it  while  in  the  lumbar  region,  and  which  are  com- 
pelled to  follow  it,  bo  to  Bpeak,  as  it  assumes  a  lower  position  in 
the  body.  Bence  the  explanation  of  the  otherwise  Btrange  fact  of 
the  origin  <>f  these  parts  at  so  considerable  a  distance  from  the 
in  t«-  which  they  arc  distributed. 

Descent  of  the  Testicles  into  Scrotum. — The  means  by  which 
the  descent  of  the  testicles  into  the  scrotum  is  effected  are  not 
fully  and  exactly  known.  It  was  formerly  believed  that  a  mem- 
branous and  partly  muscular  curd,  called  the  gubernaculum  testis, 
which  extends  while  the  testicle  is  yet  high  in  the  abdomen,  from 
its  lower  part,  through  the  abdominal  wall  (in  the  situation  of  the 
inguinal  canal)  to  the  front  of  the  pubes  and  lower  part  of  the 
scrotum,  was  the  agent  by  the  contraction  of  which  the  descent 
was  effected.  It  is  now  generally  believed,  however,  that  such  is 
not  the  case;  and  that  the  descent  of  the  testicle  and  ovary  is 
rather  the  result  of  a  general  process  of  development  in  these  and 
neighbouring  parts,  the  tendency  of  which  is  to  produce  this 
change  in  the  relative  position  of  tie  -  _->ns.  In  other  words, 
the  descent  is  not  the  result  of  a  mere  mechanical  action,  by 
which  the  organ  is  dragged  down  to  a  lower  position,  but  rather 
one  change  out  of  many  which  attend  the  gradual  development 
and  re-arrangement  of  these  organs.  It  maybe  repeated,  however, 
that  the  details  of  the  process  by  which  the  descent  of  the  testicle 
into  the  scrotum  is  effected  are  not  accurately  known. 

The  homologue,  in  the  female,  of  the  gubernaculum  testis,  is  a 
structure  called  the  round  ligament  of  the  utt  rus,  which  extends 
through  the   inguinal   canal,   from  the  outer  ami  upper  part  of 
the  uterus  to  the  .subcutaneous  tissue  in  front  of  the  symphys 
pubis. 

At  a  very  early  _  <.f  fcetal  life,  the  Wolffian  ducts,  ureters, 
and  Mi'illerian  ducts,  open  into  a  receptacle  formed  by  the  lower 
end  of  the  allantois,  or  rudimentary  bladder;  and  as  this  com- 
municates with  the  lower  extremity  of  the  intestine,  there  is  for 


8i6 


GENERATION  AND  DEVELOPMENT. 


[CHAP.   XX. 


the  time,  a'common  receptacle  or  cloaca  for  all  these  parts,  which 
opens  to  the  exterior  of  the  body  through  a  part  corresponding 
with    the    future    anus,  an  arrangement   which  is  permanent   in 

Reptiles,  Birds,  and  some 
of  the  lower  Mammalia. 
In  the  human  foetus, 
however,  the  intestinal 
portion  of  the  cloaca  is 
cut  off  from  that  which 
belongs  to  the  urinary 
and  generative  organs  ; 
a  separate  passage  or 
canal  to  the  exterior  of 
the  body,  belonging  to 
these  parts,  being  called 
the  sinus  urogenital!*. 
Subsequently,  this  canal 
is  divided,  by  a  process 
of  division  extending 
from  before  backwards 
or  from  above  down- 
wards, into  a  '  pars 
urinaria '  and  a  '  pars 
genitalis.'  The  former, 
continuous  with  the 
urachus,  is  converted 
into  the  urinary  blad- 
der. 

The  Fallopian  tubes,  the  uterus,  and  the  vagina  are  developed 
from  the  Mullerian  ducts  (fig.  464,  m  and  fig.  465)  whose  first 
appearance  has  been  already  described.  The  two  Mullerian  ducts 
are  united  below  into  a  single  cord,  called  the  genital  cord,  and, 
from  this  are  developed  the  vagina,  as  well  as  the  cervix  and  the 
lower  portion  of  the  body  of  the  uterus ;  while  the  ununited  por- 
tion of  the  duct  on  each  side  forms  the  upper  part  of  the  uterus, 
and  the  Fallopian  tube.  In  certain  cases  of  arrested  or  abnormal 
development,  these  portions  of  the  Mullerian  ducts  may  not 
become  fused  together  at  their  lower  extremities,  and  there  is  left 
a  cleft  or  horned  condition  of  the  upper  part  of  the  litems  re- 


i'i 


.  464.  —  Diagram  of  the  Wolffian  hoilit-s,  Mullerian 
ducts  ami  adjacent  parts  previous  to  sexual  distinc- 
tion, as  seen  from  before,  sr,  the  supra-renal 
bodies  ;  r,  the  kidneys  ;  ot,  common  blastema  of 
ovaries  or  testicles  ;  W,  Wolffian  bodies  ;  w,  Wolf- 
fian ducts ;  m,  m,  Mullerian  ducts ;  <j  c,_  genital 
cord ;  ug,  sinus  urogenitalis ;  i,  intestine ;  cl, 
cloaca.     (Allen  Thompson.) 


chap,  xx.]      URINARY   AND  GENERATIVE  ORGANS; 


817 


sembling  a  condition  which  is  permanent  in  certain  of  the  lower 

animals. 

In  the  male,  the  Rfullerian  ducts  have  do  special  function,  and 
are  but  slightly  developed.  The  hydatid  of  Morgagni  is  the 
remnant  of  the  upper  part   of  the  Mullerian  duct.     The  small 


Fig.  465. 


Fig.  466. 


Urinary  and  generative  organs  of  a  human  female  embryo,  measuring  3K  inches  in  length . 

pig  46^. —General  view  of  these  parts  ;  i,  supra-renal  capsules;  2,  kidneys  ;  3,  ovary;  4, 

Fallopian  tube  ;  5,  uterus;  6,  intestine  ;  7,  the  bladder. 
Fi"  466  —Bladder  and  Generative  organs  of  the  same  embryo  viewed  from  the  side  ;  a, 
3  the  urinarv  bladder  (at  the  upper  part  is  a  portion  of  the  urachus)  ;  2,  urethra  ;  3, 

uterus   (with  two  cornua)  ;  4.  vagina;  5.  part  as   yet  common  to  the  vagina  ana 

urethra;  6,  common  orifice  of  the  urinary  and  generative  organs  ;  7,  the  clitoris. 
Yirr    ,67  —Internal  generative  organs  of  the  same  embryo;  1,  the  uterus;  2,  the  round 
"'ligaments  ;  3,  the  Fallopian  tubes  (formed  by  the  Mullerian  ducts)  ;  4,  the  ovaries ;  5, 

the  remains  of  the  "Wolffian  bodies. 
Fig.  468.— External   generative   organs  of  the  same  embryo;  1,  the  labia  majora;    2, 

the  nymphse  ;  3,  clitoris  ;  4,  anus.     (Midler). 

prostatic  pouch,  uterus  masculinus,  or  sinus  poadaris,  forms  the 
atrophied  remnant  of  the  distal  cud  of  the  genital  cord,  and  is,  of 
course,  therefore,  the  homologue,  in  the  male,  of  the  vagina  and 
uterus  in  the  female. 

3    G 


8i8  GENERATION    AND    DEVELOPMENT.  [chap.  xxi. 

The  external  parts  of  generation  are  at  first  the  same  in  both 
sexes.  The  opening  of  the  genito-urinary  apparatus  is,  in  both 
sexes,  bounded  by  two  folds  of  skin,  whilst  in  front  of  it  there  is 
formed  a  penis-like  body  surmounted  by  a  glans,  and  cleft  or 
furrowed  along  its  under  surface.  The  borders  of  the  furrows 
diverge  posteriorly,  running  at  the  sides  of  the  genito-urinary 
orifice  internally  to  the  cutaneous  folds  just  mentioned  (see 
figs.  465,  466,  467).  In  the  female,  this  body  becoming  retracted, 
forms  the  clitoris,  and  the  margins  of  the  furrow  on  its  under 
surface  are  converted  into  the  nymphse,  or  labia  minora,  the  labia 
majora  pudenda  being  constituted  by  the  great  cutaneous  folds. 
In  the  male  foetus,  the  margins  of  the  furrow  at  the  under  surface 
of  the  penis  unite  at  about  the  fourteenth  week,  and  form  that 
part  of  the  urethra  which  is  included  in  the  penis.  The  large 
cutaneous  folds  form  the  scrotum,  and  later  (in  the  eighth  month 
of  development),  receive  the  testicles,  which  descend  into  them 
from  the  abdominal  cavity.  Sometimes  the  urethra  is  not  closed, 
and  the  deformity  called  hypospadias  then  results.  The  appearance 
of  hermaphroditism  may,  in  these  cases,  be  increased  by  the 
retention  of  the  testes  within  the  abdomen. 


CHAPTER   XXL" 

ON  THE  RELATION  OF  LIFE  TO  OTHER  FORCES. 

An  enumeration  of  theories  concerning  the  nature  of  life  would 
be  beside  the  purpose  of  the  present  chapter.  They  are  interest- 
ing as  marks  of  the  way  in  which  various  minds  have  been 
influenced  by  the  nrystery  which  has  alwa}'s  hung  about  vitality ; 
their  destruction  is  but  another  warning  that  any  theory  we  can 
frame  must  be  considered  only  a  tie  for  connecting  present  facts, 
and  one  that  must  yield  or  break  on  any  addition  to  the  number 
which  it  is  to  bind  together. 

*  This  chapter  is  a  reprint,  with  some  verbal  alterations,  of  an  essay- 
contributed  to  St.  Bartholomew's  Hospital  Reports,  1867,  by  W.  Morrant 
Baker. 


chap.  xxi. J    THE   RELATION   OE  LIFE  TO   OTHER    FORCES,    819 

Before  attention  had  been  drawn  to  the  mutual  convertibility 
<>f  the  various  so-called  physical   forces-^heat,  light,  electricity, 

and  ethers — and  until  it  had  been  shown  that  these,  like  the 
matter  through  which  they  act,  are  limited  in  amount,  and 
strictly  measurable  ;  that  a  given  quantity  of  one  force  can 
produce  a  certain  quantity  of  another  and  no  more  ;  that  a 
given  quantity  of  combustible  material  can  produce  only  a  given 
quantity  of  steam,  and  this  again  only  so  much  motive  power; 
it  was  natural  that  men's  minds  should  be  satisfied  m with  the 
thought  that  vital  force  was  some  peculiar  innate  power,  un- 
limited by  matter,  and  altogether  independent  of  structure  and 
organisation.  The  comparison  of  life  to  a  flame  is  probably  as 
early  as  any  thought  about  life  at  all.  And  so  long  as  light  and 
heat  were  thought  to  be  inherent  qualities  of  certain  material 
which  perished  utterly  in  their  production,  it  is  not  strange  that 
life  also  should  have  been  reckoned  some  strange  spirit,  pent  up 
in  the  germ,  expending  itself  in  growth  and  development,  and 
finally  declining  and  perishing  with  the  body  which  it  had  in- 
habited. 

With  the  recognition,  however,  of  a  distinct  correlation  between 
the  physical  forces,  came  as  a  natural  consequence  a  revolution  of 
the  commonly  accepted  theories  concerning  life  also.  The  dictum, 
so  long  accepted,  that  life  was  essentially  independent  of  physical 
force  began  to  be  questioned. 

As  it  is  well-nigh  impossible  to  give  a  definition  of  life  that 
shall  be  short,  comprehensive,  and  intelligible,  it  will  be  best, 
perhaps,  to  take  its  chief  manifestations,  and  see  how  far  these 
seem  to  be  dependent  on  other  forces  in  nature,  and  how  connected 
with  them. 

Life  manifests  itself  by  Birth,  Growth,  Development,  Decline 
and  Death;  and  an  idea  of  life  will  most  naturally  arise  by 
taking  these  events  in  succession,  and  studying  them  individually, 
and  in  relation  to  each  other. 

When  the  embryo  in  a  seed  awakes  from  that  state,  neither 
life  nor  death,  which  is  called  dormant  vitality,  and,  bursting  its 
envelopes,  begins  to  grow  up  and  develope,  it  maybe  said  that 
there  is  a  birth.  And  so,  when  the  chick  escapes  from  the  e^, 
and  when  any  living  form  is,  as  the  phrase  goes,  brought  into  the 
world.     In  each  case,  however,  birth  is  not  the  beginning  of  life, 

3  g  2 


820    THE   RELATION   OF   LIFE   TO   OTHER   FORCES.   [.  hap.  xxi. 

but  only  the  continuation  of  it  under  different  conditions.  To 
understand  the  beginning  of  life  in  any  individual,  -whether  plant 
or  animal,  existence  must  be  traced  somewhat  further  back,  and 
in  this  way  an  idea  gained  concerning  the  nature  of  the  germ,  the 
development  of  which  is  to  issue  in  birth. 

The  genu  may  be  denned  as  that  portion  of  the  parent  which 
is  set  apart  with  power  to  grow  up  into  the  likeness  of  the  being 
from  which  it  has  been  derived. 

The  manner  in  which  the  germ  is  separated  from  the  parent 
does  not   here  concern  us.     It  belongs  to  the  special  subject  of 
generation.     Neither  need   we  consider  apart  from  others  those 
modes  of  propagation,    as   fission    and    gemmation,   which    differ 
more  apparently  than  really  from  the  ordinary  process  typified  in 
the  formation  of  the  seed  or  ovum.     In  every  case  alike,  a  new 
individual  plant  or  animal  is  a  portion  of  its  parent  :  it  may  be 
a   mere   outgrowth   or   bud,  which,  if  separated,  can  maintain  an 
independent  existence  :   it  may  be  not  an  outgrowth  but  simply 
a  portion  of  the  parent's  structure,  which  has  been  naturally  or 
artificially  cut  off,  as  in  the  spontaneous  or  artificial  cleaving  of 
a  polype  ;  it  may  be  the  embryo  of  a  seed  or  ovum,  as  in  th 
cases   in  which  the  process   of  multiplication  of  different  organs 
has  reached  the  point  of  separation  of  the  individual  more  or  less 
completely  into  two  sexes,  the  mutual  conjugation   of  a  portion 
of  each  of  which,  the  sperni-cell  and  the  gemi-cell,  is  necessary 
for  the  production  of  a  new  being.     "We   are   so  accustomed  to 
regard  the  conjugation  of  the  two   sexes   as  necessary  for  what 
is   called  generation,  that   we  are  apt  to  forget   that  it   is  only 
gradually  in  the  upward  progress  of  development  of  the  vege- 
table   and    animal    kingdoms,    that    those    portions    of   organised 
matter  which   are  to  produce  new    beings    are    allotted   to   two 
separate  individuals.     In  the  least  developed  forms  of  life,  alm<  st 
any  part  of  the  body  is  capable  of  assuming  the  characters   of  a 
separate  individual  ;  and  propagation,  therefore,  occurs  by  fission 
or  gemmation  in   some  form  or   other.      Then,  in  beings  a  little 
higher   in   rank,   only  a  special   part   of  the  body  can  become  a 
separate  being,  and  only  by  conjugation  with  another  special  part. 
Still,  there   is  but   one   parent  ;  and  this  hennaphrodite-forni   of 
generation  is  the  rule  in  the  vegetable  and  least  developed  portion 
«.f  the  animal  kingdom.     At  last,  in   all  animals  bat  the  low-;--. 


chap,  xxi.]    THE   RELATION   OF   LIFE  TO   OTHEB    FOBCES,    S21 

and  in  .some  plants,  the  portions  of  organised  structure  specialised 
for  development  after  their  mutual  union  into  a  new  individual, 
are  found  on  two  distinct  beings,  which  we  call  respectively  male 
and  female. 

Tin.' eld  idea  concerning  the  power  of  growth  resident  in  thi 
in  of  the  new  being,  thus  formed  in  various  ways,  was  ex- 
pressed by  Baying  that  a  store  of  dormant  vitality  was  laid  up 
in  it,  and  that  so  long  as  no  decomposition  ensued,  this  \ 
capable  of  manifesting  itself  and  becoming  active  under  the 
influence  of  certain  external  conditions.  Thus,  the  dormant  force 
supposed  to  be  present  in  the  seed  or  the  egg  was  assumed  to  be 
the  primary  agent  in  effecting  development  and  growth,  and  to 
continue  in  action  during  the  whole  term  of  life  of  the  living 
being,  animal  or  vegetable,  in  which  it  was  said  to  reside.  The 
influence  of  external  forces — heat,  light,  and  others — was  noticed 
and  appreciated  ;  hut  these  were  thought  to  have  no  other  connec- 
tion with  vital  force  than  that  in  some  way  or  other  they  called  it 
into  action,  and  that  to  some  extent  it  was  dependent  on  them 
for  its  continuance.  They  were  not  supposed  to  be  correlated  with 
it  in  any  other  sense  than  this. 

Now,  however,  we  are  obliged  to  modify  considerably  our 
notions  and  with  them  our  terms  of  expression,  when  describing 
the  origin  and  birth  of  a  new  being. 

To  take,  as  before,  the  simplest  case — a  seed  or  egg.  We 
must  suppose  that  the  heat,  which  in  conjunction  with  moisture 
is  necessary  for  the  development  of  those  changes  which  issue 
in  the  growth  of  a  new  plant  or  animal,  is  not  simply  an  agent 
which  so  stimulates  the  dormant  vitality  in  the  seed  or  egg  as 
to  make  it  cause  growth,  but  it  is  a  force,  which  is  itself 
transformed  into  chemical  and  vital  power.  The  embryo  in 
the  seed  or  egg  is  a  part  which  can  transform  heat  into  vital 
force,  this  term  being  a  convenient  one  wherewith  to  expre>> 
the  power  which  particular  structures  possess  of  growing, 
developing,   and  performing   other   actions  which   we  call   vital.* 


*  The  term  •' vital  force"  is  here  employed  for  the  sake  of  brevity. 
"Whether  it  is  strictly  admissible  will  be  discussed  hereafter. 

The  general  term  force  is  used  as  synonymous  with  what  is  now  often 
termed  energy. 


S22    THE   RELATION   OF   LIFE   TO    OTHER   FORCES,   [chap.  xxi. 

Of  course  the  embryo  can  grow  only  by  taking  up  fresh  material 
and  incorporating  it  with  its  own  structure,  and  therefore  it  is 
surrounded  in  the  seed  or  ovum  with  matter  sufficient  for  nutri- 
tion until  it  can  obtain  fresh  supplies  from  without.  The 
absorption  of  this  nutrient  matter  involves  an  expenditure  of 
force  of  some  kind  or  other,  inasmuch  as  it  implies  the  raising 
of  simple  to  more  complicated  forms.  Hence  the  necessity  for 
heat  or  some  other  power  before  the  embryo  can  exhibit  any 
sign  of  life.  It  would  be  quite  as  impossible  for  the  genu  to 
begin  life  without  external  force  as  without  a  supply  of  nutrient 
matter.  Without  the  force  wherewith  to  take  it,  the  matter 
would  be  useless.  The  heat,  therefore,  which  in  conjunction  with 
moisture  is  necessary  for  the  beginning  of  life,  is  partly  expended 
as  chemical  power,  which  causes  certain  modifications  in  the 
nutrient  material  surrounding  the  embryo,  e.g.,  the  transforma- 
tion of  starch  into  sugar  in  the  act  of  germination  :  partly,  it  is 
transformed  by  the  germ  itself  into  vital  force,  whereby  the 
germ  is  enabled  to  take  up  the  nutrient  material  presented  to  it, 
and  arrange  it  in  forms  characteristic  of  life.  Thus  the  force  is 
expended,  and  thus  life  begins — when  a  particle  of  organised 
matter,  which  has  itself  been  produced  by  the  agency  of  life, 
begins  to  transform  external  force  into  vital  force,  or  in  other 
words  into  a  power  by  which  it  is  enabled  to  grow  and  develop. 
This  is  the  true  beginning  of  life.  The  time  of  birth  is  but  a 
particular  period  in  the  process  of  development  at  which  the 
o-emi.  haying  arrived  at  a  fit  state  for  a  more  independent 
existence,  steps  forth  into  the  outer  world. 

The  term  "  dormant  vitality."  must  be  taken  to  mean  simply 
the  existence  of  organised  matter  with  the  capacity  of  transform- 
ing heat  or  other  force  into  vital  or  growing  power,  when  this 
force  is  applied  to  it  under  proper  conditions. 

The  state  of  dormant  vitality  is  like  that  of  an  empty  voltaic 
battery,  or  a  steam-engine  in  which  the  fuel  is  not  yet  lighted. 
In  the  former  case  no  electric  current  pa>>cs.  because  no  chemical 
action  is  going  on.  There  is  no  transformation  into  electric  force, 
because  there  is  no  chemical  force  to  be  transformed.  Yet,  we  do 
not  say,  in  this  instance,  that  there  is  a  store  of  electricity  laid  up 
in  a  dormant  state  in  the  battery  ;  neither  do  we  say  that  a  store 
of  motion  is  laid  up  in  the  steam-engine.     And  there  is  as  little 


rim-,  wi.]    THE   RELATION   OF   LIFE  TO   OTHEfc    FORCES.    823 

ii  for  Baying  there  is  a  store  of  vitality  in  a  dormant  seed  or 
ovum. 

Next  to  the  beginning  of  life,  we  have  to  consider  how  far  its 
continuance  by  growth  and  development  is  dependent  on  external 
force  and  to  what  extent  correlated  with  it. 

M.  re  growth  is  not  a  special  peculiarity  of  living  beings.  A 
crystal,  if  placed  in  a  proper  solution,  will  increase  in  size  and 
preserve  its  own  characteristic  outline;  and  even  if  it  be  injured, 
the  flaw  can  be  in  part  or  wholly  repaired.  The  manner  of  its 
growth,  however,  is  very  different  from  that  of  a  living  being, 
and  the  process  as  it  occurs  in  the  latter  will  be  made  more 
evident  by  a  comparison  of  the  two  cases.  The  increase  of  a 
crystal  takes  place  simply  by  the  laying  of  material  on  the  sur- 
face only,  and  is  unaccompanied  by  any  interstitial  change.  This 
is,  however,  but  an  accidental  difference.  A  much  greater  one  is 
to  be  found  in  the  fact  that  with  the  growth  of  a  crystal  there  is 
no  decay  at  the  same  time,  and  proceeding  with  it  side  by  side. 
Since  there  is  no  life  there  is  no  need  of  death — the  one  being  a 
condition  consequent  on  the  other.  During  the  whole  life  of  a 
living  being,  on  the  other  hand,  there  is  unceasing  change.  At 
different  periods  of  existence  the  relation  between  waste  and 
repair  is  of  course  different.  In  early  life  the  addition  is  greater 
than  the  loss,  and  so  there  is  growth  ;  the  reconstructed  part  is 
better  than  it  was  before,  and  so  there  is  development.  In  the 
decline  of  life,  on  the  contrary,  the  renewal  is  less  than  the 
destruction,  and  instead  of  development  there  is  degeneration. 
But  at  no  time  is  there  perfect  rest  or  stability. 

It  must  not  be  supposed,  therefore,  that  life  consists  in  the 
capability  of  resisting  decay.  Formerly,  when  but  little  or 
nothing  was  known  about  the  laws  which  regulate  the  existence 
of  living  beings,  it  was  reasonable  enough  to  entertain  such  an 
idea  ;  and,  indeed,  life  was  thought  to  be,  essentially,  a  myste- 
rious power  counteracting  that  tendency  to  decay  which  is  so 
evident  when  life  has  departed.  Now,  we  know  that  so  far  from 
life  preventing  decomposition,  it  is  absolutely  dependent  upon  it 
for  all  its  manifestations. 

The  reason  of  this  is  very  evident.  Apart  from  the  doctrine 
of  correlation  of  force,  it  is  of  course  plain  that  tissues  which  do 
work  must  sooner  or  later  wear  out  if   not  constantly  supplied 


324    THE  DELATION   OF  LIFE   TO   OTHER   FOPX'ES.   [chap.  xxi. 

with  nourishment  ;  and  the  need  of  a  continual  supply  of  food,  on 
the  one  hand,  and,  on  the  other,  the  constant  excretion  of  matter 
which,  having  evidently  discharged  what  was  required  of  it,  was 
fit  only  to  be  cast  out,  taught  this  fact  very  plainly.  But  although, 
to  a  certain  extent,  the  dependence  of  vital  power  on  supplies  of 
matter  from  without  was  recognised  and  appreciated,  the  true 
relation  between  the  demand  and  supply  was  not  until  recently 
thoroughly  grasped.  The  doctrine  of  the  correlation  of  vital 
with  other  forces  was  not  understood. 

To  make  this  more  plain,  it  will  be  well  to  take  an  instance  of 
transformation  of  force  more  commonly  km  rwn  and  appreciated. 
In  the  steam-engine  a  certain  amount  of  force  is  exhibited  as 
motion,  and  the  immediate  agent  in  the  production  of  this  is 
steam,  which  again  is  the  result  of  a  certain  expenditure  of  heat. 
Thus,  heat  is  in  this  instance  said  to  be  transformed  into  motion, 
or,  in  other  language,  one — molecular — mode  of  motion,  heat, 
is  made  to  express  itself  by  another — mechanical — mode,  ordinary 
movement.  But  the  heat  which  produced  the  vapour  is  itself  the 
product  of  the  combustion  of  fuel,  or,  in  other  words,  it  is  the 
correlated  expression  of  another  force — chemical,  namely,  that 
afnnitv  of  carbon  and  hydrogen  for  oxygen  which  is  satisfied  in 
the  act  of  combustion.  Again,  the  production  of  light  and  heat 
by  the  burning  of  coal  and  wood  is  only  the  giving  out  again 
of  that  heat  and  light  of  the  sun  which  were  used  in  their  pro- 
duction. For,  as  it  need  scarcely  be  said,  it  is  only  by  means  of 
these  solar  forces  that  the  leaves  of  plants  can  decompose  carbonic 
acid,  <fcc,  and  thereby  provide  material  for  the  construction  of 
woody  tissue.  Thus,  coal  and  wood  being  products  of  the  ex- 
penditure of  force,  must  be  taken  to  represent  a  certain  amount  of 
power  j  and,  according  to  the  law  of  the  correlation  of  forces, 
must  be  capable  of  yielding,  in  some  shape  or  other,  just  so 
much  as  was  exercised  in  their  formation.  The  amount  of  force 
requisite  for  rending  asunder  the  elements  of  carbonic  acid  is 
exactly  that  amount  which  will  again  be  manifested  when  they 
clash  together  again. 

The  sun,  then,  really,  is  the  prime  agent  in  the  movement  of 
the  steam-engine,  as  it  is  indeed  in  the  production  of  nearly  all 
the  power  manifested  on  this  globe.  In  this  particular  instance, 
speaking  roughly,  its  light  and  heat  are   manifested  successively 


chap,  xxi.]    THE   RELATION   OF   LIFE  To   OTHEB    FORCES.    825 

as  vital  and  chemical  force  in  the  growth  of  plants,  as  heat  and 
light  again  in  the  burning  fuel,  and  Lastly  by  the  piston  and 
wheels  of  the  engine  as  motive  power.  We  may  use  the  term 
transformation  of  force  if  we  will,  or  say  that  throughout  the 
cycle  <»f  changes   there  is  hut   one    force   variously   manifesting 

itself.  It  matters  not,  So  that  we  keep  clearly  ill  view  the  notion 
that  all  force,  so  far  at  least  as  our  present  knowledge  extends, 
is  hut  a  representative,  it  may  he  in  the  same  form  or  another, 
of  some  previous  force,  and  incapable  like  matter,  of  being 
created  afresh,  except  by  the  Creator.  Much  of  our  knowledge 
on  this  subject  is  of  course  confined  to  ideas,  and  governed  by 
the  words  with  which  we  are  compelled  to  express  them,  rather 
than  to  actual  things  or  facts  ;  and  probably  the  term  force  will 
soon  lose  the  signification  which  we  now  attach  to  it.  What  is 
now  known,  however,  about  the  relation  of  one  force  to  another, 
is  not  sufficient  for  the  complete  destruction  of  old  ideas  ;  and, 
therefore,  in  applying  the  examples  of  transformation  of  physical 
force  to  the  explanation  of  vital  phenomena,  we  are  compelled  still 
to  use  a  vocabulary  which  was  framed  for  expressing  many  notions 
now  obsolete. 

The  dependence  of  the  lowest  kind  of  vital  existence  on  external 
force,  and  the  manner  in  which  this  is  used  as  a  means  whereby 
life  is  manifested,  have  been  incidentally  referred  to  more  than 
once  when  describing  the  origin  of  vegetable  tissues.  The  main 
functions  of  the  vegetable  kingdom  are  construction,  and  the 
perpetuation  of  the  race  ;  and  the  use  which  is  made  of  external 
physical  force  is  more  simple  than  in  animals.  The  transformation 
indeed  which  is  effected,  while  much  less  mysterious  than  in  the 
latter  instance,  forms  an  interesting  link  between  animal  and 
crystalline  growth. 

The  decomposition  of  carbonic  acid  or  ammonia  by  the  leaves 
of  plants  may  be  compared  to  that  of  water  by  a  galvanic  current. 
In  both  cases  a  force  is  applied  through  a  special  material  medium, 
and  the  result  is  a  separation  of  the  elements  of  which  each 
compound  is  formed.  On  the  return  of  the  elements  to  their 
original  state  of  union,  there  will  be  the  return  also  in  some  form 
or  other  of  the  force  which  was  used  to  separate  them.  Vegetable 
growth,  moreover,  with  which  we  are  now  specially  concerned, 
resembles  somewhat  the  increase  of  unorganised   matter.      The 


826    THE  RELATION   OF  LIFE  TO   OTHER  FORCES,   [chap.  xxi. 

accidental  difference  of  its  being  in  one  case  superficial,  and  in  the 
other  interstitial,  is  but  little  marked  in  the  process  as  it  occurs 
in  the  more  permanent  parts  of  vegetable  tissues.  The  layers  of 
lignine  are  in  their  arrangement  nearly  as  simple  as  those  of  a 
crystal,  and  almost  or  quite  as  lifeless.  After  their  deposition, 
moreover,  they  undergo  no  further  change  than  that  caused  by  the 
addition  of  fresh  matter,  and  hence  the}*  are  not  instances  of  that 
ceaseless  waste  and  repair  which  have  been  referred  to  as  so 
characteristic  of  the  higher  forms  of  living  tissue.  There  is,  how- 
ever, no  contradiction  here  of  the  axiom,  that  where  there  is  life 
there  is  constant  change.  Those  parts  of  a  vegetable  organism  in 
which  active  life  is  going  on  are  subject,  like  the  tissues  of  animals, 
to  constant  destruction  and  renewal.  But,  in  the  more  permanent 
parts,  life  ceases  with  deposition  and  construction.  Addition  of 
fresh  matter  may  occur,  and  so  may  decay  also  of  that  which  is 
already  laid  down,  but  the  two  processes  are  not  related  to  each 
other,  and  not,  as  in  living  parts,  inter-dependent.  Hence  the 
change  is  not  a  vital  one. 

The  acquirement  in  growth,  moreover,  of  a  definite  shape  in  the 
case  of  a  tree,  is  no  more  admirable  or  mysterious  than  the  pro- 
duction of  a  crystal.  That  chloride  of  sodium  should  naturally 
assume  the  form  of  a  cube  is  as  inexplicable  as  that  an  acorn 
should  grow  into  an  oak,  or  an  ovum  into  a  man.  When  we 
learn  the  cause  in  the  one  case  we  shall  probably  in  the  other 
also. 

There  is  nothing,  therefore,  in  the  products  of  life's  more 
simple  forms  that  need  make  us  start  at  the  notion  of  their 
being  the  products  of  only  a  special  transformation  of  ordinary 
physical  force,  and  we  cannot  doubt  that  the  growth  and  de- 
velopment of  animals  obey  the  same  general  laws  that  govern  the 
formation  of  plants.  The  connecting  links  between  them  are  too 
numerous  for  the  acceptance  of  any  other  supposition.  Both 
kingdoms  alike  are  expressions  of  vital  force,  which  is  itself  but  a 

OX  ' 

term  for  a  special  transformation  of  ordinary  physical  force.  The 
mode  of  the  transformation  is,  indeed,  mysterious,  but  so  is  that 
of  heat  into  light,  or  of  either  into  mechanical  motion  or  chemical 
affinity.  All  forms  of  life  are  as  absolutely  dependent  on  external 
physical  force  as  a  fire  is  dependent  for  its  continuance  on  a  supply 
of  fuel ;  and  thei-e  is  as  much  reason  to  be  certain  that  vital  force 


dHAP.  kxl]  THK   RELATION   OF   LIFE  TO   (iTHl'.l:    FOBCES.    827 
is  an  expression  or  representation  of  the  physical  forces,  especially 

heat  and  Light,  as  that  these   are  the   correlates  of  some  force  or 

Other  which  has  acted  or  is  acting  on  the  substances  which,  as  WQ 
say,  produce  them. 

In  the  tissues  of  plants,  as  just  said,  there  is  hut  little  change, 
except  such  as  is  produced  by  additions  of  fresh  matter.  That 
which  is  once  deposited  alters  but  little;  or,  if  the  part  be  tran- 
sient and  easily  perishable,  the  alteration  is  only  or  chiefly  one 
produced  by  the  ordinary  process  of  decay.  Little  or  no  force  is 
manifested  ;  or,  if  it  be,  it  is  only  the  heat  of  the  slow  oxidation 
whereby  the  structure  again  returns  to  inorganic  shape.  There  is 
no  special  transformation  of  force  to  which  the  term  vital  can  be 
applied.  With  construction  the  chief  end  of  vegetable  existence 
has  been  attained,  and  the  tissue  formed  represents  a  store  of 
force  to  be  used,  but  not  by  the  being  which  laid  it  up.  The 
labours  of  the  vegetable  world  are  not  for  itself  but  for  animals. 
The  power  laid  up  by  the  one  is  spent  by  the  other.  Hence  the 
reason  that  the  constant  change,  which  is  so  great  a  character  of 
life,  is  comparatively  but  little  marked  in  plants.  It  is  present, 
but  only  in  living  portions  of  the  organism,  and  in  these  it  is  but 
limited.  In  a  tree  the  greater  part  of  the  tissues  may  be  con- 
sidered dead  ;  the  only  change  they  suffer  is  that  fresh  matter  is 
piled  on  to  them.  They  are  not  the  seat  of  any  transformation 
of  force,  and  therefore,  although  their  existence  is  the  result  of 
living  action,  they  do  not  themselves  live.  Force  is,  so,  to  speak, 
laid  up  in  them,  bnt  they  do  not  themselves  spend  it.  Those 
portions  of  a  vegetable  organism  which  are  doing  active  vital 
work — which  are  using  the  sun's  light  and  heat,  as  a  means 
whereby  to  prepare  building  material,  are,  however,  the  seat  of 
unceasing  change.  Their  existence  as  living  tissue  depends  upon 
this  fact — upon  their  capability  of  perishing  and  being  renewed. 

And  this  leads  to  the  answer  to  the  question,  What  is  the 
cause  of  the  constant  change  which  occurs  in  the  living  parts 
of  animals  and  vegetables,  which  is  so  invariable  an  accompani- 
ment of  life,  that  we  refuse  the  title  of  "living"  to  parts  not 
attended  by  it]  It  is  because  all  manifestations  of  life  are  exhibi- 
tions of  power,  and  as  no  power  can  be  originated  by  us  :  as, 
according  to  the  doctrine  of  con-elation  of  force,  all  power  is  but 
the  representative  of  some  previous  force  in  the  same  or  another 


828    THE   RELATION   OF   LIFE   TO   OTHER   FORCES,   [chap.  xxi. 

form,  so,  for  its  production,  there  must  be  expenditure  and  change 
somewhere  or  other.  For  the  vital  actions  of  plants  the  light  and 
heat  of  the  sun  are  nearly  or  quite  sufficient,  and  there  is  no  need 
of  expenditure  of  that  store  of  force  which  is  laid  up  in  them- 
selves ;  but  with  animals  the  case  is  different  They  cannot 
directly  transform  the  solar  forces  into  vital  power ;  they  must 
seek  it  elsewhere.  The  great  use  of  the  vegetable  kingdom  is 
therefore  to  store  up  power  in  such  a  form  that  it  can  be  used  by 
animals ;  that  so,  when  in  the  bodies  of  the  latter,  vegetable 
organised  material  returns  to  an  inorganic  condition,  it  may  give 
out  force  in  such  a  manner  that  it  can  be  transformed  by  animal 
tissues,  and  manifested  variously  by  them  as  vital  power. 

Hence,  then,  we  must  consider  the  waste  and  repair  attendant 
on  living  growth,  and  development  as  something  more  than  these 
words,  taken  by  themselves,  imply.  The  waste  is  the  return  to  a 
lower  from  a  higher  form  of  matter ;  and,  in  the  fall,  force  is 
manifested.  This  force,  when  specially  transformed  by  organised 
tissues,  we  call  vital.  In  the  repair,  force  is  laid  up.  The  analogy 
with  ordinary  transmutations  of  physical  force  is  perfect.  By  the 
expenditure  of  heat  in  a  particular  manner  a  weight  can  be  raised. 
By  its  fall  heat  is  returned.  The  molecular  motion  is  but  the 
expression  in  another  form  of  the  mechanical.  So  with  life.  There 
is  constant  renewal  and  decay,  because  it  is  only  so  that  vital 
activity  can  take  place.  The  renewal  must  be  something  more 
than  replacement,  however,  as  the  decay  must  be  more  than 
simple  mechanical  loss.  The  idea  of  life  must  include  both  storing 
up  of  force,  and  its  transformation  in  the  expenditure. 

Hence  we  must  be  careful  not  to  confound  the  mere  preservation 
of  individual  form  under  the  circumstances  of  concurrent  waste 
and  repair,  with  the  essential  nature  of  vitality. 

Life,  in  its  simplest  form,  has  been  happily  expressed  by 
Savory  as  a  state  of  dynamical  equilibrium,  since  one  of  its  most 
characteristic  features  is  continual  decay,  yet  with  maintenance  for 
the  individual  by  equally  constant  repair.  Since,  then,  in  the 
preservation  of  the  equilibrium  there  is  ceaseless  change,  it  is  not 
static  equilibrium  but  dynamical. 

Care  must  be  taken,  however,  not  to  accept  the  term  in  too 
strict  a  sense,  and  not  to  confound  that  which  is  but  a  necessary 
attendant  on  life  with  life  itself.     For,  indeed,  strictly,  there  is  no 


chap,  xxi.]   THE   RELATION   OF    LIFE  TO  OTHER   FOBCES,    829 

preservation  of  equilibrium  during  life.  Bach  vital  act  is  an 
advance  towards  death.  We  are  accustomed  to  make  use  of  the 
terms  growth  and  development  in  the  sense  of  progress  in  one 
direction,  and  the  words  decline  and  decay  with  an  opposite  signi- 
fication, as  if,  like  the  ebb  of  the  tide,  there  were  after  maturity 
a  reversal  of  life's  current.  But,  to  use  an  equally  old  comparison, 
life  is  really  a  journey  always  in  one  direction.  It  is  an  ascent, 
more  and  more  gradual  as  the  summit  is  approached,  so  gradual 
that  it  is  impossible  to  say  when  development  ends  and  decline 
begins.  But  the  descent  ison  the  other  side.  There  is  no  perfect 
equilibrium,  no  halting,  no  turning  back. 

The  term,  therefore,  must  be  used  with  only  a  limited  significa- 
tion. There  is  preservation  of  the  individual,  yet,  although  it  may 
seem  a  paradox,  not  of  the  same  individual.  A  man  at  one  period 
of  his  life  may  retain  not  a  particle  of  the  matter  of  which  formerly 
he  was  composed.  The  preservation  of  a  living  being  during 
growth  and  development  is  more  comparable,  indeed,  to  that  of  a 
nation,  than  of  an  individual  as  the  term  is  popularly  understood. 
The  elements  of  which  it  is  made  up  fulfil  a  certain  work  the 
traditions  of  which  were  handed  down  from  their  predecessors,  and 
then  pass  away,  leaving  the  same  legacy  to  those  that  follow  them. 
The  individuality  is  preserved,  but,  like  all  things  handed  down 
by  tradition,  its  fashion  changes,  until  at  last,  perhaps,  scarce  any 
likeness  to  the  original  can  be  discovered.  Or,  as  it  sometimes 
happens,  the  alterations  by  time  are  so  small  that  we  wonder,  not 
at  the  change,  but  the  want  of  it.  Yet,  in  both  cases  alike,  the 
individuality  is  preserved,  not  by  the  same  individual  elements 
throughout,  but  by  a  succession  of  them. 

Again,  concurrent  waste  and  repair  do  not  imply  of  necessity 
the  existence  of  life.  It  is  true  that  living  beings  are  the  chief 
instances  of  the  simultaneous  occurrence  of  these  things.  But 
this  happens  only  because  the  conditions  under  which  the  functions 
of  life  are  discharged  are  the  principal  examples  of  the  necessity 
for  this  unceasing  and  mingled  destruction  and  renewal.  They 
are  the  chief,  but  not  the  only  instances  of  this  curious  con- 
junction. 

A  theoretical  case  will  make  this  plain.  Suppose  an  instance 
of  some  permanent  structure,  say  a  marble  statue.  If  we  imagine 
it  to  be  placed  under  some   external  conditions  by  which  each 


330    THE   RELATION   OF   LIFE   TO    OTHER    FORCES,    [chap.  xxi. 

particle  of  its  substance  should  waste  and  be  replaced,  yet  with 
maintenance  of  its  original  size  and  shape,  we  obtain  no  idea  of  life. 
There  is  waste  and  renewal,  with  preservation  of  the  individual 
form,  but  no  vitality.  And  the  reason  is  plain.  With  the  waste 
<>f  a  substance  like  carbonate  of  calcium  whose  attractions  are 
satisfied,  there  would  be  no  evolution  of  force ;  and  even  if  there 
were,  no  structure  is  present  with  the  power  to  transform  or 
manifest  anew  any  power  which  might  be  evolved.  With  the 
repair,  likewise,  there  would  be  no  storing  of  force.  The  part  used 
to  make  good  the  loss  is  not  different  from  that  which  disappeared. 
There  is  therefore  neither  storing  of  force,  nor  its  transformation, 
nor  its  expenditure ;  and  therefore  there  is  no  life. 

But  real  examples  of  the  preservation  of  an  individual  substance 
under  the  circumstances  of  constant  loss  and  renewal,  may  be 
found,  yet  without  any  semblance  in  them  of  life. 

Chemistry,  perhaps,  affords  some  of  the  neatest  and  best 
examples  of  this.  One,  suggested  by  Shepard,  seems  particularly 
apposite.  It  is  the  case  of  trioxide  of  nitrogen  (X203)  in  the 
preparation  of  sulphuric  acid.  The  gas  from  which  this  acid  is 
obtained  is  sulphur  dioxide,  and  the  addition  of  an  equivalent  of 
oxygen  and  the  combination  of  the  resulting  sulphur  trioxide 
(S03)  with  water  (H20)  is  all  that  is  required.     Thus  : 

SO,         +       0         +     H,0    =       H„SO+ 
Sulph.  dioxide  :  Oxygen  :  Water  =  Sulphuric  Acid. 

Sulphur  dioxide,  however,  cannot  take  the  necessary  oxygen 
directly  from  the  atmosphere,  but  it  can  abstract  it  from  trioxide 
of  nitrogen  (XX),),  when  the  two  gases  are  mingled.  The 
trioxide,  accordingly,  by  continually  giving  up  an  equivalent  of 
oxygen  to  an  equivalent  of  sulphur  dioxide,  causes  the  formation 
of  sulphuric  acid,  at  the  same  time  that  it  retains  its  composition 
by  continually  absorbing  a  fresh  quantity  of  oxygen  from  the 
atmosphere. 

In  this  instance,  then,  there  is  constant  waste  and  repair,  yet 
without  life.  And  here  an  objection  cannot  be  raised,  as  it  might 
be  to  the  preceding  example,  that  both  the  destruction  and  repair 
come  from  without,  and  are  not  dependent  on  any  inherent 
qualities  of  the  substance  with  which  they  have  to  do.  The  waste 
and  renewal  in  the  last-named  example  are  strictly  dependent  on 


chap,  xxi.]   THE   ELELATI03   OF    LIFE  TO   OTHEB    FORCES.    831 

the  qualities  of  the  chemical  compound  which  is  Bubject  to  them. 
It  haa  but  to  be  placed  in  appropriate  conditions,  and  destruction 
and  repair  will  continue  indefinitely.  Force,  too,  is  manifested, 
but  there  is  nothing  present  which  can  transform  it  into  vital 
shape,  and  bo  there  is  no  life. 

Hence,  our  notion  of  the  constant  decay  which,  together  with 
repair,  takes  place  throughout  life,  must  be  not  confined  to  any 
-imply  mechanical  act.  It  must  include  the  idea,  as  before  said, 
of  laying  up  of  force,  and  its  expenditure — its  transformation  too, 
in  the  act  of  being  expended. 

The  gn.wth,  then,  of  an  animal  or  vegetable,  implies  the  ex- 
penditure of  physical  force  by  organized  tissue,  as  a  means 
whereby  fresh  matter  is  added  to  and  incorporated  with  that 
already  existing.  In  the  case  of  the  plant  the  force  used,  trans- 
formed, and  stored  up,  is  almost  entirely  derived  from  external 
sources  ;  the  material  used  is  inorganic.  The  result  is  a  tissue 
which  is  not  intended  for  expenditure  by  the  individual  which  has 
accumulated  it.  The  force  expended  ingrowth  by  animals,  on  the 
other  hand,  cannot  be  obtained  directly  from  without.  For  them 
a  supply  of  force  is  necessary  in  the  shape  of  food  derived  directly 
or  indirectly  from  the  vegetable  kingdom.  Part  of  this  force- 
containing  food  is  expended  as  fuel  for  the  production  of  power  ; 
and  the  latter  is  used  as  a  means  wherewith  to  elaborate  another 
portion  of  the  food,  and  incorporate  it  as  animal  structure.  Un- 
like vegetable  structure,  however,  animal  tissues  are  the  seat  of 
constant  change,  because  their  object  is  not  the  storing  up  of 
power,  but  its  expenditure ;  so  there  must  be  constant  waste  ;  and 
if  this  happen,  then  for  the  continuance  of  life  there  must  be- 
equally  constant  repair.  But,  as  before  said,  in  early  life  the 
repair  surpasses  the  loss,  and  so  there  is  growth.  The  part 
repaired  is  better  than  before  the  loss,  and  thus  there  is  develop- 
ment. 

The  definite  limit  which  has  been  imposed  on  the  duration  of 
life  has  been  already  incidentally  referred  to.  Like  birth,  growth, 
and  development,  it  belongs  essentially  to  living  beings  only. 
Dead  structures  and  those  which  have  never  lived  are  subject  to 
change  and  destruction,  but  decay  in  them  is  uncertain  in  its 
beginning  ami  continuance.  It  depends  almost  entirely  on  ex- 
ternal conditions,  and  differs  altogether  from  the  decline  of  life. 


832    THE  RELATION   OF  LIFE   TO   OTHER   FORCES,    [chap.  xxr. 

The  decline  and  death  of  living  beings  are  as  definite  in  their 
occurrence  as  growth  and  development.  Like  these  they  may  be 
hastened  or  stayed,  especially  in  the  lower  forms  of  life,  by  various 
influences  from  without ;  but  the  putting  off  of  decline  must  be 
the  putting  off  also  of  so  much  life ;  and,  apart  from  disease,  the 
reverse  is  true  also.  A  living  being  starts  on  its  career  with  a 
certain  amount  of  work  to  do — various  infinitely  in  different 
individuals,  but  for  each  well-defined.  In  the  lowest  members  of 
both  the  animal  and  vegetable  creation  the  progress  of  life  in  any 
given  time  seems  to  depend  almost  entirely  on  external  circum- 
stances ;  and  at  first  sight  it  seems  almost  as  if  these  lowly-formed 
organisms  were  but  the  sport  of  the  surrounding  elements.  But 
it  is  only  so  in  appearance,  not  in  reality.  Each  act  of  their  life 
is  so  much  expended  of  the  time  and  work  allotted  to  them ;  and 
if,  from  absence  of  those  surrounding  conditions  under  which 
alone  life  is  possible,  their  vitality  is  stayed  for  a  time,  it  again 
proceeds  on  the  renewal  of  the  necessary  conditions,  from  that 
point  which  it  had  already  attained.  The  amount  of  life  to  be 
manifested  by  any  given  individual  is  the  same,  whether  it  takes 
a  day  or  a  year  for  its  expenditure.  Life  may  be  of  course  at  any 
moment  interrupted  altogether  by  disease  and  death.  But  sup- 
posing it,  in  any  individual  organism,  to  run  its  natural  course, 
it  will  attain  but  the  same  goal,  whatever  be  its  rate  of  move- 
ment. Decline  and  death,  therefore,  are  but  the  natural  termina- 
tions of  life  ;  they  form  part  of  the  conditions  on  which  vital  action 
begins ;  they  are  the  end  towards  which  it  naturally  tends. 
Death,  not  by  disease  or  injury,  is  not  so  much  a  violent  interrup- 
tion of  the  course  of  life,  as  the  attainment  of  a  distant  object 
which  was  in  view  from  the  commencement. 

In  the  period  of  decline,  as  during  growth,  life  consists  in 
continued  manifestations  of  transformed  physical  force  ;  and  there 
is  of  necessity  the  same  series  of  changes  by  which  the  individual, 
though  bit  by  bit  perishing,  yet  by  constant  renewal  retains  its 
entity.  The  difference,  as  has  been  more  than  once  said,  is  in  the 
comparative  extent  of  the  loss  and  reproduction.  In  decline  there 
is  not  perfect  replacement  of  that  which  is  lost.  Repair  becomes 
less  and  less  perfect,  It  does  not  of  necessity  happen  that  there 
is  any  decrease  of  the  quantity  of  material  added  in  the  place  of 
that  which  disappears.     But  although  the  quantity  mnj  not  be 


chap,  wi.l   THE   ELELATION  OF   LIFE  TO   OTHEB   FORCES.    833 

aed,  and  may  indeed  absolutely  increase,  it  is  not  perfe< 
material  for  repair,  and  although  there  may  be  no  wasting,  there 
ia  degeneration, 

N<>  definite  period  can  be  assigned  as  existing  between  the  end 
of  development  and  the  beginning  <>f  decline,  and  chiefly  because 
the  two  pro©  0  "li  side  by  side  in  different  parts  of  the  same 

organism.  The  transition  as  a  whole  is  therefore  too  gradual  for 
appreciation.  But,  after  some  time,  all  parts  alike  share  in  the 
tendency  to  degeneration  ;  until  at  length,  being  no  longer  able  to 
Bubdue  externa]  force  to  vital  shape,  they  die;  and  the  elements 
of  which  they  are  composed  simply  employ  what  remnant  of 
power,  in  the  shape  of  chemical  affinity,  is  still  left  in  them, 
as  a  means  whereby  they  may  go  back  to  the  inorganic  world. 
Of  course  the  same  process  happens  constantly  during  life ;  but 
in  death  the  place  of  the  departing  elements  is  uot  taken  by 
others. 

Here,  then,  a  sharp  boundary  line  is  drawn  where  one  kind  of 
action  stops  and  the  other  begins;  where  physical  force  ceases  to 
be  manifested  except  as  physical  force,  and  where  no  further 
vital  transformation  takes  place,  or  can  in  the  body  ever  do  so. 
For  the  notion  of  death  must  include  the  idea  of  impossibility  of 
revival,  as  a  distinction  from  that  state  of  what  is  called  "dor- 
mant vitality,"  in  which,  although  there  is  no  life,  there  is  capabi- 
lity of  living.  Hence  the  explanation  of  the  difference  between 
the  effect  of  appliance  of  external  force  in  the  two  cases.  Take, 
for  examples,  the  fertile  but  not  yet  living  egg,  and  the  barren  or 
dead  one.  Every  application  of  force  to  the  one  must  excite 
movement  in  the  direction  of  development;  the  force,  if  used  at 
all,  is  transformed  by  the  germ  into  vital  energy,  or  the  power  by 
which  it  can  gather  up  and  elaborate  the  materials  for  nutrition 
by  which  it  is  surrounded.  Hence  its  freedom  throughout  the 
brooding  time  from  putrefaction.  In  the  other  instance,  the  appli- 
ance of  force  excites  only  degeneration;  if  transformed  at  all,  it 
is  only  into  chemical  force,  whereby  the  progress  of  destruction  is 
hastened  ;  hence  it  soon  rots.  To  the  one,  heat  is  the  signal  for 
development,  to  the  other  for  decay.  By  one  it  is  taken  up  and 
manifested  anew,  and  in  a  higher  form  ;  to  the  other  it  gives 
the  impetus  for  a  still  quicker  fall. 

Life,  then,  does  not  stand  alone.      It  is  but  a  special  manifesta- 

3  H 


834    THE   RELATION   OF  LIFE   TO    OTHER   FORCES,    [chap,  xxi 

tion  of  transformed  force.  "  But  if  this  be  so,"  it  may  be  said — 
"  if  the  resemblance  of  life  to  other  forces  be  great,  are  not  the 
differences  still  greater  1 " 

At  the  first  glance,  the  distinctions  between  living  organised 
tissue  and  inorganic  matter  seem  so  great  that  the  difficulty  is  in 
finding  a  likeness.  And  there  is  no  doubt  that  these  wide  differ- 
ences in  both  outward  configuration  and  intimate  composition  have 
been  mainly  the  causes  of  the  delay  in  the  recognition  of  the  claims 
of  life  to  a  place  among  other  forces.  And  reasonably  enough. 
For  the  notion  that  a  plant  or  an  animal  can  have  any  kind  of 
relationship  in  the  discharge  of  its  functions  to  a  galvanic  battery 
or  a  steam  engine  is  sufficiently  startling  to  the  most  credulous. 
But  so  it  has  been  proved  to  be. 

Among  the  distinctions  between  living  and  unorganised  matter, 
that  which  includes  differences  in  structure  and  proximate  chemi- 
cal composition  has  been  always  reckoned  a  great  one.  The  very 
terms  organic  and  inorganic  were,  until  quite  recently,  almost 
sj'noirymous  with  those  which  implied  the  influence  of  life  and  the 
want  of  it.  The  science  of  chemistry,  however,  is  a  great  leveller 
of  artificial  distinctions,  and  many  complex  substances  which,  it 
was  supposed,  could  not  be  formed  without  the  agency  of  life  can 
be  now  made  directly  from  their  elements  or  from  very  simple 
combinations  of  these.  The  number  of  complex  substances  so 
formed  artificially  is  constantly  increasing ;  and  there  seems  to  be 
no  reason  for  doubting  that  even  such  as  albumin,  gelatin,  and  the 
like,  will  be  ultimately  produced  without  the  intermediation  of 
living  structure. 

The  formation  of  the  latter,  such  an  organised  structure  for 
instance  as  a  cell  or  a  muscular  fibre,  is  a  different  thing  alto- 
gether. There  is  at  present  no  reason  for  believing  that  such 
will  ever  be  formed  by  artificial  means ;  and,  therefore,  among  the 
peculiarities  of  living  force-transforming  agents,  must  be  reckoned 
as  a  great  and  essential  one,  a  special  intimate  structure,  apart 
from  mere  ultimate  or  proximate  chemical  composition,  to  which 
there  is  no  close  likeness  in  any  artificial  apparatus,  even  the 
most  complicated.  This  is  the  real  distinction,  as  regards  com- 
position, between  a  living  tissue  and  an  inorganic  machine  ; 
namely,  the  difference  between  the  structural  arrangement  by 
which  force  is  transformed  and  manifested  anew.     The  fact  that 


cdhap.xxi.]   THE  RELATION   OF   LIFE  TO  OTHEB  FOECB8.    835 

one  agent  for  transforming  force  is  made  of  albumen  or  tin-  Like, 
and  another  of  sine  or  iron,  is  a  great  distinction,  but  not  so 
essential  or  fundamental  an  one  as  the  difference  in  mechanical 
structure  and  arrangement. 

In  proceeding  to  consider  the  difference  between  what  may  be 
called  the  transformation-products  of  living  tissue,  and  of*  an  arti- 
ficial machine,  it  will  be  well  to  take  one  of  the  simple  cases  first 
— the  production  of  mechanical  motion;  and  especially  because  it 
is  so  common  in  both. 

In  one  we  can  trace  the  transformation.  We  know,  as  a  fact, 
that  heat  produces  expansion  (steam),  and  by  constructing  an 
apparatus  which  provides  for  the  application  of  the  expansive 
power  in  opposite  directions  alternately,  or  by  alternating  con- 
traction with  expansion,  we  arc  able  to  produce  motion  so  as  to 
subserve  an  infinite  variety  of  purposes.  For  the  continuance  of 
the  motion  there  must  be  a  constant  supply  of  heat,  and  therefore 
of  fuel. 

In  the  production  of  mechanical  motion  by  the  alternate  con- 
tractions of  muscular  fibres  we  cannot  trace  the  transformation  of 
force  at  all.  We  know  that  the  constant  supply  of  force  is  as 
necessary  in  this  instance  as  in  the  other  ;  and  that  the  food 
which  an  animal  absorbs  is  as  necessary  as  the  fuel  in  the  former 
case,  and  is  analogous  with  it  in  function.  In  what  exact  rela- 
tion, however,  the  latent  force  in  the  food  stands  to  the  movement 
in  the  fibre,  we  are  at  present  quite  ignorant.  That  in  some  way 
or  other,  however,  the  transformation  occurs,  we  may  feel  quite 
certain. 

There  is  another  distinction  between  the  two  exhibitions  of 
force  which  must  be  noticed.  It  has  been  universally  believed, 
almost  up  to  the  present  time,  that  in  the  production  of  living- 
force  the  result  is  obtained  by  an  exactly  corresponding  waste 
of  the  tissue  which  produces  it ;  that,  for  instance,  the  power  of 
each  contraction  of  a  muscle  is  the  exact  equivalent  of  the  force 
produced  by  the  more  or  less  complete  descent  of  so  much  mus- 
cular substance  to  inorganic,  or  less  complex  organic  shape ;  in 
other  words, — that  the  immediate  fuel  which  an  animal  requires 
for  the  production  of  force  is  derived  from  its  own  substance  ; 
and  that  the  food  taken  must  first  be  appropriated  by,  and  enter 
into  the  very  formation  of  living  tissue  before  its  latent  force  can 

3  11  2 


836    THE  RELATION   OF  LIFE  TO   OTHER  FORCES,    [chap.  xxi. 

be  transformed  and  manifested  as  vital  power.  And  here,  it  might 
be  said,  is  a  great  distinction  between  a  living  structure  and  a 
simply  mechanical  arrangement  such  as  that  which  has  been  used 
for  comparison  ;  the  fuel  which  is  analogous  to  the  food  of  a  plant 
or  animal  does  not,  as  in  the  case  of  the  latter,  first  form  part  of 
the  machine  which  transforms  its  latent  energy  into  another  variety 
of  power. 

"We  are  not,  at  present,  in  a  position  to  deny  that  this  is  a 
real  and  great  distinction  between  the  two  cases;  but  modern 
investigations  in  more  than  one  direction  lead  to  the  belief  that 
we  must  hesitate  before  allowing  such  a  difference  to  be  an 
universal  or  essential  one.  The  experiments  referred  to  seem 
conclusive  in  regard  to  the  production  of  muscular  power  in 
greater  amount  than  can  be  accounted  for  by  the  products  of 
muscular  waste  excreted ;  and  it  may  be  said  with  justice,  that 
there  is  no  intrinsic  improbability  in  the  supposed  occurrence  of 
transformation  of  force,  apart  from  equivalent  nutrition  and  sub- 
sequent destruction  of  the  transforming  agent.  Argument  from 
analogy,  indeed,  would  be  in  favour  of  the  more  recent  theory  as 
the  likelier  of  the  two. 

Whatever  may  be  the  result  of  investigations  concerning  the 
relation  of  waste  of  living  tissue  to  the  production  of  power, 
there  can  be  no  doubt,  of  course,  that  the  changes  in  any  part 
which  is  the  seat  of  vital  action  must  be  considerable,  not  only 
from  what  may  be  called  "  wear  and  tear,"  but,  also,  on  account 
of  the  great  instability  of  all  organised  structures.  Between 
such  waste  as  this,  however,  and  that  of  an  inorganic  machine 
there  is  only  the  difference  in  degree,  arising  necessarily  from 
diversity  of  structure,  of  elemental  arrangement,  and  so  forth. 
But  the  repair  in  the  two  cases  is  different.  The  capability  of 
reconstruction  in  a  living  body  is  an  inherent  quality  like  that 
which  causes  growth  in  a  special  shape  or  to  a  certain  degree* 
At  present  we  know  nothing  really  of  its  nature,  and  we  are 
therefore  compelled  to  express  the  fact  of  its  existence  by  such 
terms  as  "  inherent  power,"  "  individual  endowment,"  and  the 
like,  and  wait  for  more  facts  which  may  ultimately  explain  it. 
This  special  quality  is  not  indeed  one  of  living  things  alone. 
The  repair  of  a  crystal  in  definite  shape  is  equally  an  "  indi- 
vidual endowment,"  or  "inherent  peculiarity,"  of  the  nature  of 


ohap.  xxi.]    THE  RELATION   OF   LIKE  TO   OTHEB    FORCES.    837 

which  we  are  equally  ignorant.  In  the  case,  however,  of  an 
inorganic  machine  there  is  nothing  of  the  sort,  not  own  as  in  a 
crystal,  Faults  of  structure  must  be  repaired  by  some  means 
entirely  from  without*  And  as  our  notion  of  a  living  being, 
Bay  a  horse,  would  be  entirely  altered  if  flaws  in  his  composition 
were  repaired  by  external  means  only  ;  BO,  in  like  manner, 
Would  our  idea  of  the  nature  of  a  steam-engine  be  completely 
changed  had  it  the  power  of  absorbing  and  using  part  of  its  fuel 
a>  matter  wherewith  t<>  repair  any  ordinary  injury  it  might  sustain. 

It  is  this  ignorance  of  the  nature  of  such  an  act  as  reconstruc- 
tion which  causes  it  to  be  said,  with  apparent  reason,  that  so  long 
as  the  term  "vital  force  "  is  used,  so  long  do  we  beg  the  question 
at  issue — What  is  the  nature  of  life  ?  A  little  consideration,  how- 
ever, will  show  that  the  justice  of  this  criticism  depends  on  the 
manner  in  which  the  word  "vital"  is  used.  If  by  it  we  intend 
to  express  an  idea  of  something  which  arises  in  a  totally  different 
manner  from  other  forces — something  which,  we  know  not  how, 
depends  on  a  special  innate  quality  of  living  beings,  and  owns  no 
dependence  on  ordinary  physical  force,  but  is  simply  stimulated 
by  it,  and  has  no  correlation  with  it — then,  indeed,  it  would  be 
just  to  say  that  the  whole  matter  is  merely  shelved  if  we  retain 
the  term  "  vital  force. " 

But  if  a  distinct  correlation  be  recognised  between  ordinary 
physical  force  and  that  which  in  various  shapes  is  manifested  by 
living  beings  ;  if  it  be  granted  that  every  act — say,  for  example, 
of  a  brain  or  muscle — is  the  exactly  correlated  expression  of  a 
certain  quantity  of  force  latent  in  the  food  with  which  an  animal 
is  nourished  ;  and  that  the  force  produced  either  in  the  shape  <  >f 
thought  or  movement  is  but  the  transformed  expression  of  external 
force,  and  can  n<>  more  originate  in  a  living  organ  without  sup- 
plies of  force  from  without,  than  can  that  organ  itself  be  formed 
or  nourished  without  supplies  of  matter  ; — if  these  facts  be  recog- 
nised, then  the  term  used  in  speaking  of  the  powers  exercised  by 
a  living  being  is  not  of  very  much  consequence.  We  have  as 
much  right  to  use  the  term  "vital''  as  the  words  galvanic  and 
chemical.  All  alike  are  but  the  expressions  of  our  ignorance 
concerning  the  nature  of  that  power  of  which  all  that  we  call 
"  forces "  are  various  manifestations.  The  difference  is  in  the 
apparatus  by  which  the  force  is  transformed. 


838    THE  RELATION   OF  LIFE   TO   OTHER   FORCES,    [chap.  xxr. 

It  is  with  this  meaning  that,  for  the  present,  the  term  "vital 
force  "  may  still  be  retained  when  we  wish  shortly  to  name  that 
combination  of  energies  which  we  call  life.  For,  exult  as  we  may 
at  the  discovery  of  the  transformation  of  physical  force  into  vital 
action,  we  must  acknowledge  not  only  that,  with  the  exception  of 
some  slight  details,  we  are  utterly  ignorant  of  the  process  by 
which  the  transformation  is  effected  ;  but,  as  well,  that  the  result 
is  in  many  ways  altogether  different  from  that  of  any  other  force 
with  which  we  are  acquainted. 

It  is  impossible  to  define  in  what  respects,  exactly,  vital  force 
differs  from  any  other.  For  while  some  of  its  manifestations  are 
identical  with  ordinary  physical  force,  others  have  no  parallel 
whatsoever.  And  it  is  this  mixed  nature  which  has  hitherto 
baffled  all  attempts  to  define  life,  and,  like  a  Will-o'-the-wisp,  has 
led  us  floundering  on  through  one  definition  after  another  only  to 
escape  our  grasp  and  show  onr  impotence  to  seize  it. 

In  examining,  therefore,  the  distinctions  between  the  products 
of  transformations  by  a  living  and  by  an  inorganic  machine,  we 
have  first  to  recognise  the  fact,  that  while  in  some  cases  the  dif- 
ference is  so  faint  as  to  be  nearly  or  quite  imperceptible,  in  others 
there  seems  not  a  trace  of  resemblance  to  be  discovered. 

In  discussing  the  nature  of  life's  manifestations — birth,  growth, 
development,  and  decline — the  differences  which  exist  between 
them  and  other  processes  more  or  less  resembling  them,  but  not 
dependent  011  life,  have  been  already  briefly  considered  and  need 
not  be  here  repeated.  It  may  be  well,  however,  to  sum  up  very 
shortly  the  particulars  in  which  life  as  a  manifestation  of  force 
differs  from  all  others. 

The  mere  acquirement  of  a  certain  shape  by  growth  is  not  a 
peculiarity  of  life.  But  the  power  of  developing  into  so  composite 
a  mass  even  as  a  vegetable  cell  is  a  property  possessed  by  an 
organised  being  only.  In  the  increase  of  inorganic  matter  there 
is  no  development,  The  minutest  crystal  of  any  given  salt  has 
exactly  the  same  shape  and  intimate  structure  as  the  largest. 
"With  the  growth  there  is  no  development.  There  is  increase  of 
size  with  retention  of  the  original  shape,  but  nothing  more.  And 
if  we  consider  the  matter  a  little  we  shall  see  a  reason  for  this. 
In  all  force-transformers,  whether  living  or  inorganic,  with  but 
few  exceptions — and  these  are,  probably,  apparent  only — some- 


chap,  zxi.]    Till:  RELATION   OF   LIFE  TO  OTHEB   FORCES.    839 

thing  more  is  required   than  homogeneity  of  structure.     There 

ems  to  l"'  a  Deed   for  Borne  mutual  dependence  of  one  pari  on 

another,  some  distinction  of  qualities,  which  cannot  happen  when 

all  portions  ore  exactly  alike.     And  here  lies  the  resemblance 

between  a  living  being  and  an  artificial  machine.  Both  are 
developments,  and  depend  for  their  power  of  transforming  force 
on  that  mutual   relation  of  the  several   parts  of  their  structure 

which  we  call  organisation.  But  here,  also,  lies  a  great  difference. 
The  development  of  a  living  being  is  due  to  an  inherent  tendency 
to  assume  a  certain  form  j  about  which  tendency  we  know  abso- 
lutely nothing.  We  recognise  the  fact,  and  that  is  all.  The 
development  of  an  inorganic  machine — say  an  electrical  apparatus 
— is  not  due  to  any  inherent  or  individual  property.  It  is  the 
result  of  a  power  entirely  from  without  ;  and  we  know  exactly 
how  to  construct  it. 

Here,  Then,  again,  we  recognise  the  compound  nature  of  a  living 
being.  In  structure  it  is  altgether  different  from  a  crystal — iu 
inherent  capacity  of  growth  into  definite  shape  it  resembles  it. 
Again,  in  the  fact  of  its  organisation  it  resembles  a  machine  made 
by  man  :  in  capacity  of  growth  it  entirely  differs  from  it.  In 
regard,  therefore,  to  structure,  growth,  and  development,  it  has 
combined  in  itself  qualities  which  in  all  other  things  are  more  or 
less  completely  separated. 

That  modification  of  ordinary  growth  and  development  called 
generation,  which  consists  in  the  natural  production  and  separa- 
tion of  a  portion  of  organised  structure,  with  power  itself  to  trans- 
form force  so  as  therewith  to  build  up  an  organism  like  the  being 
from  which  it  was  thrown  off,  is  another  distinctive  peculiarity  of 
a  living  being.  We  know  of  nothing  like  it  in  the  inorganic 
world.  And  the  distinction  is  the  greater  because  it  is  the  ful- 
filment of  a  purpose,  towards  which  life  is  evidently,  from  its 
very  beginning,  constantly  tending.  It  is  as  natural  a  destiny  to 
separate  parts  which  shall  form  independent  beings  as  it  is  to 
develop  a  limb.  Hence  it  is  another  instance  of  that  carrying  out 
of  certain  projects,  from  the  very  beginning  in  view,  which  is  so 
characteristic  of  things  living  and  of  no  other. 

It  is  especially  in  the  discharge  of  what  are  called  the  animal 
functions  that  we  see  vital  force  most  strangely  manifested.  It  is 
true  that  one  of  the  actions  included  in  this  term — namely  mecha- 


S40    THE   RELATION   OF   LIFE   TO   OTHER   FORCES,    [chap.  xxi. 

nical  movement — although  one  of  the  most  striking,  is  by  no  means 
a  distinctive  one.  For  it  must  be  remembered  that  one  of  the 
commonest  transformations  of  physical  force  with  which  we  are 
acquainted  is  that  of  heat  into  mechanical  motion,  and  that  this 
may  be  effected  by  an  apparatus  having  itself  nothing  whatever  to 
do  with  life.  The  peculiarity  of  the  manifestation  in  an  animal  or 
vegetable  is  that  of  the  organ  by  which  it  is  effected,  and  the 
manner  in  which  the  transformation  takes  place,  not  in  the  ulti- 
mate result.  The  mere  fact  of  an  animal's  possessing  capability 
of  movement  is  not  more  wonderful  than  the  possession  of  a 
similar  property  by  a  steam  engine.  In  both  cases  alike,  the 
motion  is  the  correlative  expression  of  force  latent  in  the  food  and 
fuel  respectively  ;  but  in  one  case  we  can  trace  the  transforma- 
tion in  the  arrangement  of  parts,  in  the  other  we  cannot. 

The  consideration  of  the  products  of  the  transformation  of  force 
effected  by  the  nervous  system  would  lead  far  beyond  the  limits 
of  the  present  chapter.  But  although  the  relation  of  mind  to 
matter  is  so  little  known  that  it  is  impossible  to  speak  with  any 
freedom  concerning  such  correlative  expressions  of  physical  force 
as  thought  and  nerve-products,  still  it  cannot  be  doubted  that 
they  are  as  much  the  results  of  transformation  of  force  as  the 
mechanical  motion  caused  by  the  contraction  of  a  muscle.  But 
here  the  mystery  reaches  its  climax.  We  neither  know  how  the* 
change  is  effected,  nor  the  nature  of  the  product,  nor  its  analogies 
with  other  forces.  It  is  therefore  better,  for  the  present,  to  con- 
fess our  ignorance,  than,  with  the  knowledge  which  we  have  lately 
gained,  to  build  up  rash  theories,  serving  only  to  cause  that  con- 
fusion which  is  worse  than  error. 

It  may  be  said,  with  perfect  justice,  that  even  if  the  foregoing 
conclusions  be  accepted,  namely,  that  all  manifestations  of  force 
by  living  beings  are  correlative  expressions  of  ordinary  plrysical 
force,  still  the  argument  is  based  on  the  assumption  of  the  existence 
of  the  apparatus  which  we  call  living  organised  matter,  with 
power  not  only  to  use  external  force  for  its  own  use  in  growth, 
development,  and  other  vital  manifestations,  but  for  that  modi- 
fication of  these  powers  which  consists  in  the  separation  of  a  part 
that  shall  grow  up  into  the  likeness  of  its  parent,  and  thus  con- 
tinue the  race.  We  are  therefore,  it  may  be  added,  as  far  as  ever 
from  any  explanation  of  the  origin  of  life.     This  is  of  course  quite 


chap.  xxi. |  THE   RELATION   OF   LIFE  TO  OTHEE   FOECES.    841 

true.  The  object  of  the  present  chapter,  however,  is  only  to  deal 
with  the  relations  of  Life,  as  it  now  exists,  to  other  forces.  The 
manner  of  creation  of  the  various  kinds  "I"  organised  matter,  and 
the  Bouroe  of  those  qualities,  belonging  to  it,  winch  from  our 
ignorance  we  call  inherent,  are  different  questions  altogether. 

To  say  that  of  necessity  the  power  to  form  living  organised 
matter  will  never  be  vouchsafed  to  us,  that  it  is  only  a  mere 
materialist  who  would  believe  in  such  a  possibility,  seems  almost 
as  absurd  as  the  statement  that  such  inquiries  lead  of  necessity 
to  the  denial  of  any  higher  power  than  that  which  in  various 
forms  is  manifested  as  "  force,"  on  this  small  portion  of  the  universe. 
It  is  almost  as  absurd,  but  not  quite.  For,  surely,  he  who  recog- 
-  the  doctrine  of  the  mutual  convertibility  of  all  forces,  vital 
and  physical,  who  believes  in  their  unity  and  imperishableness, 
should  be  the  last  to  doubt  the  existence  of  an  all-powerful  Being, 
of  whose  will  they  are  but  the  various  correlative  expressions  ; 
from  whom  they  all  come  ;  to  whom  they  return. 


APPENDIX. 


The  Chemical  Basis  of  the  Human  Body. 

Of  the  sixty-four  known  chemical  elements  no  less  than  seventeen 
have  been  found,  in  larger  or  smaller  quantities,  to  form  the  chemical 

basis  of  the  animal  body. 

Tin-  substances  occurring  in  largest  quantities  are  the  non-metallic 
elements,  Oxygen,  Carbon,  Hydrogen,  and  Nitrogen — oxygen  and 
carbon  making  up  altogether  about  85  per  cent,  of  the  whole.  The 
most  abundant  of  the  metallic  elements  are  Calcium,  Sodium,  and 
Potassium. 

Tin:  following  table  represents  the  relative  proportion  of  the  various 
elements. — (Marshall). 

Oxygen 

Carbon  .... 

Hydrogen   . 

Nitrogen 

Calcium 

Phosphorus     . 

Sulphur 

Sodium 

Chlorine 

Compounds. — The  elementary  substances  above-mentioned  seldom 
occur  free  or  uncombined  in  the  animal  body ;  but  are  nearly 
always  united  among  themselves  in  various  numbers,  and  in  variable 
proportions  to  form  "  coin  pun  mis."  Several  elements  have,  however, 
been  detected  in  small  amount  free  ;  traces  of  uncombined  Oxygen  and 
Nitrogen  have  been  found  in  the  blood,  and  of  Hydrogen  as  well  as  of 
Oxygen  and  Nitrogen  in  the  intestinal  canal. 

Organic  and  Inorganic  Compounds. — It  was  formerly  thought 
that  the  more  complex  compounds  built  up  by  the  animal  or  vegetable 
organism  were  peculiar,  and  could  not  be  made  artificially  by  chemists 
from  their  elements  and  under  this  idea  they  were  formed  into  a 
distinct  class,  termed  organic.  This  idea  has  been  given  up,  but  the 
name  is  still  in  use,  with  a  different  signification  The  term  organic 
is  now  applied  simply  to  the  compounds  of  the  element  Carbon, 
irrespective    of   their    complexity  ;    chemists    having    found    that   these 


72 'O 

Fluorine 

.         •     . 

•08   ' 

135 

Potassium  . 

•026 

9-1 

Iron 

. 

•01 

2  "5 

Magnesium 

•0012 

1 '3 

Silicon  . 

•0002 

ii5 

(Traces  of  copper, 

lead,  and 

•1476 

•1 

•0S5 

aluminium)     . 

lOO 

S44  APPENDIX. 

compounds  are  so  numerous  and  important,  and  that  they  include 
all  those  to  which  the  term  organic  was  in  former  times  exclusively 
given. 

Characteristics  of  Organic  Compounds. — The  animal  organic 
compounds  are  characterized  as  a  rule  by  their  complexity,  for,  in  the 
first  place  many  elements  enter  into  their  composition,  thereby  dis- 
tinguishing them  from  bodies  such  as  water  (H2  O),  hydrochloric  acid 
(HC1),  and  ammonia  (X  PL),  which  may  he  taken  as  type.-  of  inorganic 
compounds.  And  again,  1  >ecause  many  atoms  of  the  same  element  occur 
in  each  molecule.  This  latter  feet  no  doubt  explains  also  the  reason  of 
the  instability  of  organic  compounds. 

Another  great  cause  of  the  instability  arises  from  the  fact  that  many  such 
compounds  contain  the  element  Nitrogen,  which  may  be  called  negative 
or  undecided  in  its  affinities,  and  may  be  easily  separated  from  com- 
bination with  other  elements. 

Animal  tissues,  containing  as  they  do  these  organic  nitrogenous  com- 
pounds, are  extremely  prone  to  undergo  chemical  decomposition,  and 
this  is  especially  the  case  since  they  also  contain  a  large  quantity  of 
water,  a  condition  most  favourable  for  the  breaking  up  of  such 
substances.  It  is  from  this  fact  that  in  the  consideration  of  the 
chemical  basis  of  the  body  we  meet  with  an  extremely  large  number  of 
decomposition  products. 

In  treating  of  the  various  substances  found  in  the  animal  organism 
it  is  convenient  to  adopt  the  division  into — 

~         .    (  a.   Nitrogenous, 
I.  (Jrqanic  <  ,     ,T      <U. 

J  b.  Non-Nitrogenous. 


2.  Inorganic. 


i.  Organic. 


(a)  Nitrogenous  bodies  take  the  chief  part  in  forming  the  solid 
tissues  of  the  body,  and  are  found  to  a  considerable  extent  in  the 
circulating  fluids  (blood,  lymph,  chyle),  the  secretions  and  excretions. 
They  contain  often  in  addition  to  Carbon,  Hydrogen,  Nitrogen,  and 
Oxygen,  the  elements  Sulphur  and  Phosphorus  ;  but  although  the 
composition  of  most  of  them  is  approximately  known,  no  general 
rational  formula  can  at  present  be  given. 

Several  classes  of  animal  nitrogenous  bodies  may  be  distinguished, 
and  it  is  convenient  to  consider  them  under  the  following  heads  : — 

(i.)  Albuminoids  or  proteids. 
(2.)   Gelatinous  substances. 
(3.)  Decomposition  nitrogenous  bodies. 

(4.)  Certain  supposed  nitrogenous  bodies,  the  exact  composition  of 
which  has  not  been  made  out. 

(1.)  Albuminoids  or  Proteids  are  the  most  important  of  the  nitro- 
genous animal  compounds,  one  or  more  of  them  entering  as  essential 


APPENDIX,  845 

parts  into  the  formation  of  all  living  tissue.      In  the  Lymph,  chyle,  and 

bl 1,  they  also  exist  abundantly.     Their  atomic  formula  is  uncertain. 

Their  composition  maybe  taken  as — 

Carbon  .         .         .     from  51*5  to  54*5 

Hydrogen       .        .     .      ,,      6o  ,,    73 

Nitrogen  ,,      15-2  ,,   17- 

Oxygen  .        .     .      „     20-9  ,,  23-5 

Sulphur  .        .  ,,        "3  ,,    2-     (Hoppe-Seyler), 

Physical  Properties. — Proteids  are  all  amorphous  and  non-crvstallisable,  so 
that  they  possess  as  a  rule  no  power  (or  scarcely  any)  of  passing  through  animal 
membranes.  They  are  soluble,  but  undergo  alteration  in  composition  in  strong 
adds  and  alkalies  ;  BOme  arc  soluble  in  water,  others  in  neutral  saline  solutions, 
some  in  dilute  acids  and  alkalies,  few  in  alcohol  or  ether.  Their  solutions  have  a 
left-handed  action  on  polarised  light. 

Chemical  Properties. — Certain  general  reactions  are  given  for  proteids.  They 
are  a  little  varied  in  each  particular  case  : — 

i. — A  solution  boiled  with  strong  nitric  acid,  becomes  yellow,  and  this 
yellowness  gets  darker  on  addition  of  ammonia  (xantho-proteic  re- 
action). 

ii. — With  potassium  ferrocyanide  and  acetic  acid,  they  give  a  white  preci- 
pitate. 

iii. — With  a  trace  of  copper  sulphate  and  an  excess  of  potassium  or  sodium 
hydrate  they  give  a  purple  coloration. 

iv. — With  Millon's  reagent  (mixed  nitrate  and  nitrite  of  mercury?),  they 
give  a  white  or  pinkish  precipitate,  becoming  more  pink  on  boiling. 

v. — When  boiled  with  sodium  sulphate  and  acetic  acid,  a  white  precipi- 
tate is  thrown  down. 

It  is  usual  to  place  Proteids  into  the  following  sub-classes,  thus  : — 
I.  II.  III. 

Native  Albumins  Derived  Albumins.     Globulin. 

Egg- Albumin.  Acid- Albumin.  (a.)  Globulin. 

Serum- Albumin.  Alkali- Albumin.  (b.)  Myosin. 

Casein.  (c.)  Fibrinoplastic  Globulin, 

(d.)  Fibrinogen, 
(e.)  Vitellin,  &c. 

IV. — Fibrin.  V. — Peptones.  VI. — Coagulated  Proteids. 

VII. — Lardacein. 


Classes  of  Proteids. 

I.  The  Native  Albumins  are  soluble  in  water  and  in  saline 
solutions  coagulable  by  heating,  not  precipitated  by  acetic  or  normal 
phosphoric  acid.  Serum-albumin  (p.  106)  is  distinguished  from  egg- 
albumin  in  being  soluble  in  ether  and  in  not  so  easily  giving  a  precipi- 
tate with  strong  hydrochloric  acid  ;  the  precipitate  being  easily  redis- 
solved  in  excess  of  the  acid.  Serum-albumin  is  found  in  the  blood, 
lymph  and  serous  and  synovial  fluids,  and  the  tissues  generally ;  it 
appears  in  the  urine  in  the  condition  known  as  albuminuria.  Two 
varieties,  metalbumin  and  'paralbumin  have  been  described  as  existing 
in  dropsical  fluids  and  ovarian  cysts  respectively. 


846  APPENDIX. 

II.  Derived  Albumins  are  made  by  adding  dilute  acids  or 
alkalies  to  solutions  of  native-albumin.     They  are  insoluble  in  water 

or  in  neutral  saline  solutions,  and  are  not  coagulated  by  heat.  Both 
the  native-albumins  and  the  next  two  classes  (iii.  and  iv.)  of  pro- 
teids  generally  undergo  change  into  either  acid-  or  alkali-albumin 
on  the  addition  of  acids  or  alkalies,  and  foods  containing  either 
albiunins  or  globulins  change  first  of  all  into  one  or  other  of  these 
compounds,  according  as  they  are  acted  upon  by  the  gastric  or  pancreatic 
juices  respectively.  Acid-albumin  is  called  also  syntmin,  and  is  either 
identical  with  or  akin  to  it.  Casein  is  very  probably  natural  alkali- 
all  iiimin,  and  exists  in  milk,  being  kept  in  solution  by  the  alkaline 
phosphates  \  it  exists  also  in  the  serum  and  serous  fluids  in  small 
quantity,  and  in  muscle.  It  is  not  coagulable  by  heat,  and  so  cor- 
responds with  the  other  derived  albumins  ;  it  is  obtainable  as  a  pre- 
cipitate by  neutralising  milk  with  acid  (acetic).  Naturally  it  is  pre- 
cipitated in  sour  milk,  on  the  formation  of  lactic  acid. 

III.  Globulins  which  comprise  the  fibrin-forming  substances  of  the 
blood  and  the  coagulable  material  in  muscle,  and  also  the  principal 
part  of  the  crystalline  lens,  yelk  of  egg,  &c.,  are  soluble  in  very  dilute 
saline  solutions,  but  not  in  distilled  water  like  the  native-albumins  ; 
on  addition  of  an  acid  or  alkali,  they  are  converted  into  the  correspond- 
ing derived-albumin.  They  are  precipitated  on  heating.  The  fol- 
lowing are  the  chief  varieties  of  globulins. 

(a.)  Globulin  or  Crystallin  is  prepared  by  nibbing  up  the  crystalline  lens  with 
sand,  adding  water  and  filtering.  On  passing  a  current  of  carbonic  acid  gas 
through  the  filtrate,  globulin  is  precipitated.  In  properties,  it  resembles  fibrino- 
plastin  and  fibrinogen,  but  cannot  apparently  produce  fibrin  in  fluids  containing 
either.     It  coagulates  at  700 — 750  C. 

(b.)  Myosin  can  be  prepared  (1)  from  dead  muscle  by  removing  all  fat,  tendon, 
&c. ,  and  washing  repeatedly  in  water,  until  the  washing  contains  no  trace  of 
proteids,  and  then  treating  with  10  per  cent,  solution  of  sodium  chloride,  which 
will  dissolve  a  large  proportion  into  a  viscid  fluid,  which  filters  with  difficulty.  If 
the  viscid  filtrate  be  dropped  little  by  little  into  a  large  quantity  of  distilled  water, 
a  white  flocculent  precipitate  of  myosin  will  occur.  (2)  Or  from  living  muscle 
by  freezing  and  rubbing  up  in  a  mortar  with  snow  and  sodium  chloride  solution 
I  per  cent.,  a  fluid  is  obtained  which  on  filtering  is  at  first  liquid,  but  will  finally 
clot,  the  clot  is  myosin. 

Myosin,  on  addition  of  dilute  acids,  dissolves  and  forms  syntonin  or  acid- 
albumin.  It  is  less  soluble  in  dilute  saline  solutions  than  (c)  and  (d).  It  coagu- 
lates at  55c — 60"  C. 

(c.)  Fibrirwplastin  or  fihrinoplastic  globidi h  or  parafffobnlin  is  prepared  from 
blood-serum  diluted  with  10  vols,  of  water,  by  pa>sing  a  current  of  carbonic  acid 
gas,  and  collecting  the  fine  precipitate  which  is  formed,  and  washing  with  water 
containing  carbonic  acid  gas.  The  current  should  be  strong  and  not  long  con- 
tinued. It  may  be  better  prepared  as  a  sticky  white  substance,  by  saturating 
serum  with  crvstallized  sodium  chloride  or  magnesium  sulphate.  (See  also  p. 
85.)     It  coagulates  at  68°— 8o°  C. 

(d.)  Fibrinogen  is  prepared  from  hydrocele  and  other  like  fluids  by  diluting  and 
passing  a  brisk  current  of  carbonic  acid  gas  (C0o)  through  the  solution  ;  or  by 
saturation  of  the  nerve  fluids  with  sodium  chloride  or  magnesium  sulphate.  (See 
also  p.  85.)     It  coagulates  at  55° — 57^  C. 

(e.)  Vitellin  can  be  prepared  from  yelk  of  egg,  in  which  it  is  probably  asso- 
ciated with  lecithin. 


APPENDIX.  847 

[V.  Fibrin  is  a  white  filamentous  body  fanned  in  the  spontaneous 

ilation  of  certain  animal   fluids.      It  is  insoluble  in  water,  except 

al  v.rv  high  temperatures,  soluble  in  dilute  acids  and  alkalies  to  a 

slight  degree,  and  in  Btrong  neutral  saline  solutions.     Soluble  also  in 

strong  acids  and  alkalies. 

It  is  prepared  by  washing  blood-clot  or  by  whipping  blood  with  a 

bundle  of  twigs.     Its   formation   in  the  hi I  has  been  already  fully 

considered. 

V.  Peptones  (or  albuminose)  are  nitrogenous  bodies  of  uncertain 
composition  made  in  the  process  of  the  digestion  of  other  proteids.  It 
is  almost  certain  that  there  arc  several  distinct  forms. 

The  great  distinction  which  exists  between  peptone  and  other  proteids 
is  their  divisibility  and  they  giving  no  precipitates  with  either  acids 
or  alkalies,  with  copper  sulphate,  ferric  chloride,  potassium  ferrocyanide 
and  acetic  acid,  oron  boiling,  and  only  with  picric  acid,  tannin,  mercuric- 
chloride,  .silver  nitrate,  and  lead  acetate.  In  addition  to  this  the 
colour  which  a  peptone  gives  with  potassium  hydrate  and  cupric 
sulphate  is  reddish  instead  of  violet. 

Kuhne  believes  that  ordinary  albumin  splits  up  under  the  action  of  the  gastric 
juice  or  pancreatic  juice  into  two  parts,  one  called  antialbumose,  and  the  other 
hcmialbnmose,  and  further  that  antialbumose  becomes  antipeptonc  and  hemial- 
bumose,  hcmipc2)tonc .  The  difference  between  hemipeptone  and  antipeptone  is 
that  the  former  can  be  further  split  up  by  the  action  of  the  pancreatic  juice.  He 
believes  that  antialbumose  is  closely  allied  to  syntonin,  and  that  the  hemialbumose 
is  more  like  myosin,  and  if  the  pepsin  be  feebly  acting,  a  body  which  he  calls 
iint ialbu mate  appears,  which  cannot  be  converted  into  peptone  by  gastric  juice, 
but  can  by  pancreatic  juice.  Solutions  of  hydrochloric  acid  or  of  sulphuric  acid, 
can  under  favourable  circumstances  partially  change  albumin  into  peptone. 

VI. — Coagulated  Proteids. — When  a    native    albumin,  or   a 

globulin  is  raised  to  a  certain  temperature  (varying  a  little  with  each 
substance)  about  70C,  it  undergoes  coagulation  and  loses  most  of  its 
original  characters.  It  becomes  insoluble  both  in  water  and  in  saline 
solutions,  and  although  soluble  in  strong  acids  and  alkalies  in  boiling, 
partially  decomposes  during  the  process.  They  are  not  soluble  in 
dilute  acids  or  alkalies,  but  dissolve  freely  under  the  action  of  the 
gastric  or  of  the  pancreatic  secretion,  being  converted  into  peptones. 

VII.  Lardacein. — Lardacein  or  amyloid  substance  is  found  in 
certain  organs  of  the  body,  chiefly  in  the  liver  as  a  morbid  deposit. 
It  is  insoluble  in  water,  and  in  saline  solutions.  It  is  unacted  upon  by 
the  digestive  juices.  It  is  coloured  red  by  iodine.  It  is  soluble  in 
acids  or  in  alkalies,  thus  forming  acid-  or  alkali-alluunin. 

(2.)  Gelatinous  principles  include  : — (1.)  Gelatin  ;  (2.)  Mucin  ; 
(3.)  Elastin  ;  (4.)  Chondrin  ;  and  (5.)  Keratin.  They  are  very  like 
the  Proteid  group,  but  exhibit  considerable  differences  among  them- 
selves. 

(i.)  Gelatin  is  produced  by  boiling  fibrous  tissue,  or  by  treating  bones  with 
acids,  whereby  their  salts  are  dissolved,  leaving  the  framework  of  gelatin,  which  is 
soluble  in  hot  water. 


348  APPENDIX. 

It  is  a  yellow,  amorphous,  transparent  body,  which  does  not  give  any  of  the 
proteid  reactions  if  pure,  insoluble  in  cold,  but  soluble  in  hot  water,  forming  a 
jelly  on  cooling.  Its  solutions  are  precipitated  by  tannin,  by  alcohol  and  by 
mercuric  chloride. 

(2.)  Mucin,  contained  in  mucus.     It  is  a  substance  of  ropy  consistency. 

Prepared  from  ox-gall  by  precipitation  with  alcohol,  and  afterwards  redissolving 
in  water,  and  reprecipitating  with  acetic  acid.  It  may  be  also  prepared  from 
diluting  mucus  with  water,  filtering,  treating  the  insoluble  portion  with  weak 
caustic  alkali,  and  precipitating  with  acetic  acid.  It  is  precipitated  by  alcohol 
and  mineral  acids,  but  dissolved  by  excess  of  the  latter — dissolved  by  alkalies.  It 
gives  the  proteid  reaction  with  Millon's  reagent,  but  not  with  cupric  sulphate 
and  potassium  hydrate.  It  is  not  precipitated  by  mercuric  chloride  or  by  tannic 
acid.     It  is  a  colloid  substance. 

(3.)  Elastin  is  the  basis  of  elastic  tissue,  it  is  soluble  only  in  strong  alkalies  on 
boiling,  strong  sulphuric  or  nitric  acid  dissolves  it  in  the  cold. 

(4.)  Chondrin  is  contained  in  the  matrix  of  hyaline  cartilage,  and  may  be  ex- 
tracted by  boiling  with  water  and  precipitating  with  acetic  acid. 

(5.)  Keratin  is  obtained  from  hair,  nails,  and  dried  skin.  It  contains  sulphur 
evidently  only  loosely  combined. 

(3.)  Decomposition  Nitrogenous  'products. — These  are  formed  by 
the  chemical  actions  which  go  011  in  digestion,  secretion,  and  nutrition. 

Most  of  the  compounds  are  amides,  which  are  acids  in  which  amidogen,  NIL, 

is  substituted  for  hydroxyl,  OH.  Amides  may  also  be  represented  as  obtained 
from  the  ammonium  salts  by  abstraction  of  water,  or  as  derived  from  one  or  more 
molecules  of  ammonia,  NH3,  by  substituting  acid  radicals  for  hydrogen.  Thus 
acetamide  may  be  written  in  any  of  the  following  ways  : — 

C  H3  C  H3  )        „   0 

CO  NH2  CO  0NH4  ]        n-  J 

or 

(C2  H3  0)'  ] 

H'       In 

H'  J 

(C„  H3  0)  being  the  radical  of  acetic  acid. 

Varieties.  —  Several  of  the  varieties  of  amides  are  represented  in  the  products 
with  which  we  have  to  do. 

(a.)  Monamide*  which  are  derived  from  a  monatomic  acid — that  is  to  say,  an 
acid  which  contains  the  carboxyl  group  COOH,  once,  by  the  substitution  of  NH„ 
for  OH  in  this  group.  In  these  compounds  if  only  one  of  the  H  in  NH3  is  replaced 
by  an  acid  radical,  a  primary  monamide  is  formed  ;  if  two,  by  acid  or  alcohol 
radicals,  a  secondary  monamide  ;  if  three,  by  acid  or  alcohol  radicals,  a  tertiary 
monamide. 

Two  monamides  are  also  formed  from  each  diatomic  acid  (i.e.,  those  which 
contain  OH  twice,  once  in  the  carboxyl  group  COOH,  and  once  in  the  alcohol 
group  Cn  H„n  OH),  both  by  the  substitution  of  XH2  for  OH,  and  therefore  having 
the  same  composition.  They  are  isomeric  and  not  identical  however,  the  one  formed 
by  the  substitution  of  NH„  for  the  alcoholic  OH  being  acid,  while  the  other  formed 
by  the  replacement  of  the  basic  hydroxyl  is  neutral.  The  acid  amides  are  called 
arnic  acids,  or  may  form  a  class  by  themselves,  called  alanines. 

Three  amides  are  obtained  from  each  diatomic  and  bibasic  acid  : — (1.)  An  acid 
amide  or  amic  acid,  derived  from  the  acid  ammonium  salt  by  abstraction  of  one. 
molecule  of  water.  (2.)  A  neutral  monamide  (or  imidc),  derived  by  abstraction 
of  two  molecules  of  water  from  the  ammonium  salts.  (3.)  A  neutral  amide  or 
(b)  Diamide,  derived  from  the  ammonium  salt  by  abstraction  of  two  molecules  of 
water.     Thus  succini-j  acid  gives  : — 


APPENDIX. 


849 


Succinamic  Acid  .        .         .        .     Ct  H4     -I  ^  QH ' 

Snccinimide <\.  n  I      XII 

-     cinamide         ....     Cfl  IIt    (CO  .\II 

(a)  Primary   Monamtdes. 
Glycin,  glycocol  or  glycocin,  or  amido-acetic  acid— 

0,  n:i(g')  c  11  o) 

H'  ]     N  or  -     :Vt    [  0   occurs  in  the  body  in  combination, 

H'  S  "■' 

as  in  the  biliary  acids,  never  free,  'jrlycocholic  acid,  when  treated  with  weak 
a  ads,  with  alkalies  or  with  baryta  water,  splits  up  into  cholic  acid  and  glycin,  or 
amido-acetic  acid.  Thus  :  'c.,„  H43  NOa  +  H,0  =  C.,,.,  H(,,0.  +  C2  Es  MOg. 
Glycocholic  acid  +  water  =  cholic  acid  +  glycin,  and  under  similar  circum- 
stances Taurocholic  acid  splits  up  into  cholic  acid  and  taurin  : — C.1t.  H4.  03 
NSO,  +  HsO  =  CM  HM)0.  +  C2  H7  NSO3,  or  amido-isethionic.  Taurocholic 
acid  +  water  =  cholic  acid  and  taurin.  Grlycin  occurs  also  in  hippnric  acid. 
It  can  be  prepared  from  gelatin  by  the  action  of  acids  or  alkalies,  it  can  also  be 
obtained  from  hippnric  acid. 

^6   tirl    ^2   J  f  <  Ti     A    j 

Leucin. — or  amido-caproic  acid,    H  -OX,  or   £T"      -  O 

H  j  ^  H^ 

occurs  normally  in  many  of  the  organs  of  the  body  and  is  a  product 
<d  the  pancreatic  digestion  of  proteids.  It  is  present  in  the  urine 
in   certain  diseases   of  the  liver  in  which  there  is  loss  of  substance, 

especially  in  acute  yellow  atrophy.      It  occurs  in  circular  oily  dis 
crystallises    in    plates,    and  can    be   prepared  either   by   boiling  horn 
shavings,   or  any  of  the   gelatins,  with   sulphuric  acid,  or  out   of  the 
products  of  pancreatic  digestion. 

CgHs02} 
Sarcosin  may  be  considered  as  meth)d  glycin,  CH3        >  N.       It    is   a 

H  S 

constituent  of  kreatin,  but  has  never  been  found  free  in  the  human  body, 

Neurin  (C5  H13  NO),  is  an  unstable  body,  which  has  been  found  in  ox  and 
gall. 

C,  H.  -) 
Taurin,  C,  H.  NS03orSOg  HO  \  N  ;  or  amido-isethionic  acid,  is  a  consti- 

tuent  of  the  bile  acid,  taurocholic  acid,  and  is  found  also  in  traces  in  the  muscles 
and  lungs.  —  See  above. 

Cystin.  C,  H.  NSO,  occurs  in  a  rare  form  of  urinary  calculus,  which  is  only 
formed  in  a  urine  of  neutral  reaction.  It  can  be  crystallised  in  hexagonal  laniinie 
of  pale  yellow  colour,  becoming  greenish  on  exposure  to  light. 

C9  H9  X03,  or  C2  H3  02  ) 
Hippuric  Acid.  C7H.  0      X,  or  benzolglycin,  a 

H  J 

normal  constituent  of  human  urine,  the  quantity  excreted  being  in- 
creased  by  a  vegetable    diet,   and   therefore  it  is   present   in  greater 

3  1 


850  APPENDIX. 

amount  in  the  urine  of  herbivora.  It  may  lie  decomposed  by  acids 
into  glycin  and  benzoic  acid.  It  crystallises  in  semi-transparent  rhombic 
prisms,  almost  insoluble  in  cold  water,  soluble  in  boiling  water.  (See 
also  p.  446). 

Tyrosin,  C9  Hu  N03,  is  found,  generally  together  with  leucin,  in  certain 
glands,  e.g.  pancreas  and  spleen;  and  chiefly  in  the  products  of  pancreatic  digestion 
or  of  the  putrefaction  of  proteids.  It  is  found  in  the  urine  in  some  diseases  of  the 
liver,  especially  acute  yellow  atrophy.  It  crystallises  in  fine  needles,  k  which 
collect  into  feathery  masses.  It  gives  the  proteid  test  with  Millon's  reagent,  and 
heated  with  strong  sulphuric  acid,  on  the  addition  of  ferric  chloride  gives  a  violet 
colour. 

Lecithin,  C42  H<,+  P  N09,  is  a  phosphoretted  fatty  body,  which  has  been 
found  mixed  with  cerebrin,  and  oleophosphoric  acid  in  the  brain.  It  is  also  found 
in  blood,  bile  and  serous  fluids,  and  in  larger  quantities  in  nerves,  pus,  yelk  of 
egg,  semen,  and  white  blood-corpuscles.  On  boiling  with  acids  it  yields  cholin, 
glyeero-phosphoric  acid,  palmic  and  oleic  acids. 

Cerebrin,  C1:  H33  N03,  is  found  in  nerves,  pus-corpuscles,  and  in  the  brain. 
Its  chemical  constitution  is  not  known.  It  is  a  light  amorphous  powder,  taste- 
less and  odourless.  Swells  up  like  starch  when  boiled  with  water,  and  is  con- 
verted by  acids  into  a  saccharine  substance  and  other  bodies.  The  so-called  Pro- 
tagon  is  a  mixture  of  lecithin  and  cerebrin. 

{h.)  Primary  Di amides  or   Ureas. 

Urea,  (XH2)2  CO,  is  the  last  product  of  the  oxidation  of  the 
albuminous  tissues  of  the  body  and  of  the  albuminous  foods.  It 
occurs  as  the  chief  nitrogenous  constituent  of  the  urine  of  man,  and  of 
some  other  animals.  It  has  been  found  in  the  blood  and  serous  fluids, 
lymph,  and  in  the  liver. 

Properties.  Crystallises  in  thin  glittering  needles,  or  in  prisms  with 
pyramidal  ends.  Easily  soluble  in  water  and  alcohol,  insoluble  in 
ether,  easily  decomposed  by  strong  acids,  readily  forms  compounds  with 
acids  and  bases,  of  which  the  chief  are  (XH2)2  COHXO,,  urea  nitrate, 
and  ((X  H2)2  C0)2  H2  C2  02  +  H2  0,  urea  oxalate. 

Constitution.- — It  is  usually  considered  to  be  a  diamide  of  carbonic 

CO  NH2   \ 

acid   which  mar   be   written     H2   X.,  or  CO  X  H,     -    which    is    CO 

H2  ) 

(H0)2,  with  (0H)'2,  replaced  by  (XH2)'2.  Some  think  it  a  monamide 
of  carbamic  acid,  CO,  OH,  XH2,  thus  CO,  XH2  XH2,  with  one  atom 
of  XH2,  or  amidogen  in  place  of  one  of  hydroxyl  OH. 

Urea  is  isomeric  with  ammonium  cyanate  C    >   q>-tt     from    which 

it  was  first  artificially  prepared. ' 

Kreatin,  C+  H9  N3  (X,  is  one  of  the  primary  products  of  muscular  disintegra- 
tion. It  is  always  found  in  the  juice  of  muscle.  It  is  generally  decomposed  in 
the  blood  into  urea  and  kreatinin,  and  seldom,  unless  under  abnormal  circum- 
stances, appears  as  such  in  the  urine.  Treated  with  either  sulphuric  or  hydro- 
chloric acid,  it  is  converted  into  kreatinin  ;  thus — 

(L  HQ  N,  0.,  =  CA  EL  N,  O  +  Ht  0. 


APPENDIX  851 

Kreatinin,  C4  H,  X   0,  u  present  in  human  urine,  derived  from  oxidation 
of  kreatin.     It  does  not  appear  to  !"■  present  in  muscle. 

(c.)   (Jbbides. 

Ureides  are  a  third  variety  of  amides,  and  maybe  considered  as  ureas 
in  which  part  of  the  hydrogen  is  replaced  by  diatomic  acid  radicals. 
Hfonoureides  contain  one  acid  radical  and  one  urea  residue;  and  divr 
reideSy  one  acid  radical  and  two  urea  residues. 

Uric  Acid,  C  H4  N4  O^,  occurs  in  the  urine,  sparingly  in  human 
urine,  abundantly  in  that  of  birds  and  reptiles,  where  it  represents  the 
chief  nitrogenous  decomposition  product.  It  occurs  also  in  the  blood, 
spleen,  liver,  and  sometimes  is  the  only  constituent  of  urinary  calculi. 
It  is  probably  converted  in  the  blood  into  urea  and  some  carbon  acid. 
It  generally  occurs  in  urine  in  combination  with  bases,  forming  urates, 
and  never  free  unless  under  abnormal  conditions.  A  deposit  of  urates 
may  occur  when  the  urine  is  concentrated  or  extremely  acid,  or  when, 
as  during  febrile  disorders,  the  conversion  of  uric  acid  into  urea  is  in- 
completely performed. 

Properties. — Crystallises  in  many  forms,  of  which  the  most  common 
are  smooth,  transparent,  rhomboid  plates,  diamond-shaped  plates, 
hexagonal  tables,  &e.  Very  insoluble  in  water,  and  absolutely  so  in 
alcohol  and  ether.  Dried  with  strong  nitric  acid  in  a  water  bath, 
a  compound  is  formed  called  alloxan,  which  gives  a  beautiful  violet  red 
with  ammonium  hydrate  (murexide),  and  a  blue  colour  with  potassium 
hydrate.  It  is  easily  precipitated  from  its  solutions  by  the  addition  of 
a  free  acid.  It  forms  both  acid  and  neutral  salts  with  bases.  The 
most  soluble  urate  is  lithium  urate. 

Composition. — Very  uncertain  ;  has  been  however  recently  produced 
artificially,  but  it  is  not  easily  decoai posed  ;  it  may  be  regarded  as 
diureide  of  tartronic  acid.  The  chief  product  of  its  decomposition  is 
urea. 

Guanin,  C5  H5  N5  0,  has  been  found  in  the  human  liver,  spleen,  and  faeces, 
but  does  not  occur  as  a  constant  product. 

Xatithin,  C,  H+  N+  02,  has  been  obtained  from  the  liver,  spleen,  thymus, 
muscle,  and  the  blood.  It  is  found  in  normal  urine,  and  is  a  constituent  of  certain 
rare  urinary  calculi. 

ffypoxantkin,  C5  H4  N4  0,  or  sarkin,  is  found  in  juice  of  flesh,  in  the  spleen, 
thymus,  and  thyroid. 

Allantoin,  C+  H0  N4  0V  found  in  the  allantoic  fluid  of  the  foetus,  and  in  the 
urine  of  animals  for  a  short  period  after  their  birth.  It  is  one  of  the  oxidation 
products  of  uric  acid,  which  on  oxidation  gives  urea. 

In  addition  to  the  amides  and  probably  related  to  them,  are  certain 
colouring  and  excrementitious  matters,  which  are  also  most  likely 
distinct  decomposition  compounds. 

Pigments,  &c. 

Bilirubin,  C„  H9  NO,,  is  the  best  known  of  the  bile  pigments.  It  id  best  made 
by  extracting  inspissated  bile  or  gall  stonea  with  water  ^  which  dissolves  the  salts, 

3  1  2 


852  APPENDIX. 

&c. ),  then  with  alcohol,  which  takes  out  cholesterin,  fatty,  and  biliary  acids. 

Hydrochloric  acid  is  then  .added,  which  decomposes  the  lime  salt  of  bilirubin  and 
removes  the  lime.  After  extracting  with  alcohol  and  ether,  the  residue  is  dried 
and  finally  extracted  with  chloroform.  It  crystallizes  of  a  bluish-red  colour.  It 
is  allied  in  composition  to  hsematin. 

Biliverdin,  Cs  H9  NO.,,  is  made  by  passing  a  current  of  air  through  an  alkaline 
solution  of  bilirubin,  and  by  precipitation  with  hydrochloric  acid.  It  is  a  green 
pigment. 

Bilifuscin,  C9  Hjj  N03,  is  made  by  treating  gall  stones  with  ether,  then  with 
dilute  acid,  and  extracting  with  absolute  alcohol.  It  is  a  non-crystallizable  brown 
pigment. 

Biliprasin  is  a  pigment  of  a  green  colour,  which  can  be  obtained  from  gall 
stones. 

Bilihumin  (Staedeler)  is  a  dark  brown  earthy-looking  substance,  of  which  the 
formula  is  unknown. 

Urobilin  occurs  in  bile  and  in  urine,  and  is  probably  identical  with  stcrcobilin, 
which  is  found  in  the  faeces. 

Uroerythrin  is  one  of  the  colouring  matters  of  the  urine.  It  is  orange  red,  and 
contains  iron. 

Melanin  is  a  dark  brown  or  black  material  containing  iron,  occurring  in  the 
lungs,  bronchial  glands,  the  skin,  hair,  and  choroid. 

Hcematin  has  been  fully  treated  of  in  Chapter  IV. 

Indican  is  supposed  to  exist  in  the  sweat  and  urine.  It  has  not  however  been 
satisfactorily  isolated. 

Indigo,  Cs  H_  N9  0,  is  formed  from  indican,  and  gives  rise  to  the  bluish  colour 
which  is  occasionally  met  with  in  the  sweat  and  urine. 

Indol,  C8  H2  N,  is  found  in  the  faeces,  and  is  formed  either  by  decomposition  of 
indigo,  or  of  the  proteid  food  materials.  It  gives  the  characteristic  disagreeable 
smell  to  faeces. 


(4.)  Nitrogenous  Bodies  of  Uncertain  Nature. 

Ferments  are  bodies  which  possess  the  property  of  exciting  chemical 
changes  in  matter  with  which  they  come  in  contact.  They  are  at 
present  divided  into  two  classes,  called  (1)  organised,  and  (2)  unorganised 
or  soluble.  (1,)  Of  the  organ ised,  yeast  may  be  taken  as  an  example. 
Its  activity  depends  upon  the  vitality  of  the  yeast  cell,  and  disappears 
as  soon  as  the  cell  dies,  neither  can  any  substance  be  obtained  from  the 
yeast  by  means  of  precipitation  with  alcohol  or  in  any  other  way  which 
has  the  power  of  exciting  the  ordinary  change  produced  by  yeast. 

(2.)  Unorganised  or  soluble  ferments  are  those  which  are  found  in 
secretions  of  glands,  or  are  produced  by  chemical  changes  in  animal  or 
vegetable  cells  in  general ;  when  isolated  they  are  colourless,  tasteless, 
amorphous  solids  soluble  in  water  and  glycerin,  and  precipitated  from 
the  aqueous  solutions  by  alcohol  and  acetate  of  lead.  Chemically 
many  of  these  are  said  to  contain  nitrogen. 

Mode  of  action. — Without  going  into  the  theories  of  how  these  un- 
organised ferments  act,  it  will  suffice  to  mention  that  : 

(1.)  Their  activity  does  not  depend  upon  the  actual  amount  of  the 
ferment  present.  (2.)  That  the  activity  is  destroyed  by  high  tempera- 
ture, and  various  concentrated  chemical  reagents,  but  increased  by 
moderate  heat,  about  40°  C,  and  by  weak  solutions  of  either  an  acid  or 


A.EPENDIX.  Q 


53 


an  alkal  ne  fluid.  (3.  The  ferments  themselves  appeal  to  undergo  n<» 
change  in  their  own  composition,  and  waste  verj  slightly  during  the 
process. 

Varieties.  —  The  chief  classes  of  unorganised  ferments  are: — 
(1.)  Amylolytic,  which  possess  the  property  of  converting  starch  into 

glucose.     They  add  a  molecule  ofwater^  and  may  be  called  hydrolytic. 

The  probable  reaction  is  as  follows  : 

II,,,  <>,  +  3  II,„  =  C„  II,,  o,  +  2C8H1006  =  3CaH120 
Starch  Water      Glucose  Dextrin  Glue 

This  shows  thai  there  is  an  intermediate  reaction,  the  starch  being 
tivst  turned  only  partly  into  glucose  and  principally  into  dextrin,  which 
is  afterwards  further  converted  into  glucose.  The  principal  amylolytic 
ferments  are  Ptyalin,  found  in  the  saliva,  and  a  ferment,  probably  dis- 
tinct in  the  pancreatic  juice  called  Amylopsin,  These  both  act  in  an 
alkaline  medium,  Amylolytic  ferments  have  been  found  in  the  Mood 
and  elsewhere. 

Conversion  of  stare!/  into  sugar. — With  reference  to  the  action  of  the  amylolytic 
ferments,  recent  observations  have  shown  that  the  starch  molecule  is  not  by  any 
means  so  simple  as  it  has  been  represented  above.  As  it  is  said  that  starchy 
materials,  in  the  form  of  wheat  and  other  cereals,  and  in  the  potato  or  its  sub- 
stitutes, form  two-thirds  of  the  total  food  of  man,  it  is  very  important  that  we 
should  note  (i)  the  changes  which  occur  in  starch  on  cooking,  and  (2)  the  series 
of  reactions  it  undergoes  daring  its  conversion  by  the  amylolytic  ferments  into 
sugar. 

(1.)  The  object  of  this  change  is  to  produce  gelatinous  or  soluble  starch.  A 
starch  granule  consists  of  two  parts  :  an  envelope  of  cellulose,  which  gives  a  blue 
colour  with  iodine  on  addition  of  sulphuric  acid,  and  of  yranulosc,  which  is  con- 
tained within  it,  giving  a  blue  with  iodine  alone.  Briicke  states  that  a  third  body 
is  contained  in  the  granule,  which  gives  a  red  with  iodine,  viz.,  eruthro-gramUose. 
On  boiling,  the  granulose  swells  up,  bursts  the  envelope,  and  the  whole  granule  is 
more  or  less  completely  converted  into  a  paste  or  into  mucilaginous  gruel. 

(2.)  Changes  which  occur  on  addition  of  an  amylolytic  ferment.  On  the 
addition  of  saliva  or  extract  of  pancreas  to  gelatinous  starch,  the  tirst  change 
noticed  is  that  the  paste  liquifies  very  quickly,  but  the  liquid  does  not  give  the 
reaction  for  dextrin  or  fur  sugar  ;  but  soon  this  latter  reaction  appears,  increasing 
very  considerably  and  quickly,  although  at  first,  in  addition,  a  reaction  of  erythro- 
dextrin,  a  red  on  addition  of  iodine,  is  found  ;  as  the  sugar  increases,  however, 
this  disappears.  At  first  the  erythrodextrin  is  mixed  with  starch,  as  the  reaction 
La  a  reddish  purple  with  iodine,  then  it  is  a  pure  red,  and  finally  a  yellowish 
brown.  As  the  sugar  continues  to  increase  the  reaction  with  iodine  disappears, 
but  it  is  said  that  dextrin  is  still  present  in  the  form  of  achroo-dextrines,  which 
give  no  reaction  with  iodine.  However  long  the  reaction  goes  on,  it  is  unlikely 
that  all  the  dextrin  becomes  BUgar. 

Next  with  regard  to  the  kind  of  sugar  formed,  it  is,  at  first  at  any  rate,  not 
>/lucose  but  maltose,  the  formula  for  winch  is  Cia  H.,2  Ou.  Maltose  is  allied  to 
saccharose  or  cane  sugar  more  nearly  than  to  glucose  ;  it  is  crystalline  ;  its  solution 
has  the  property  of  polarising  light  to  a  greater  degree  than  solutions  of  glucose  ; 
is  not  so  sweet,  and  reduces  copper  sulphate  less  easily.  It  can  be  converted  into 
glucose  by  boiling  with  dilute  acids. 

According  to  Brown  and  Heron  the  reactions  may  be  represented  thus  : — 


8  54 


APPENDIX. 


One  molecule  of   gelatinous  starch  is  converted  into  n  molecules  of  soluble 

starch. 
One  molecule  of  soluble  starch  =  10  (C1?  H,0  0lo)  +  8  (H,  0) 

=  I  Ervthro-dextrin  'giving  red  with  iodine)  .Maltose. 

9  (C1S  H20  010)     _  +  (Cja  H22  Ou) 

=  2.   Ervthro-dextrin  (giving  vellow  with  iodine)     Maltose. 

8  (C12  H20  010)  +  2  (C12  H22  0X1) 

—  3.  Achroo-dextrin  Maltose. 

7  (0M  H20  010)  +  3  (C12  H22  0  J 

And  so  on  ;  the  resultant  being  : — 

10  (C12  H20  OJ  +  8  <H2  0)  =  8  (C12  H22  OJ  +  2  (C12  H20  0 J 
Soluble  starch     W  ater  Maltose  Achroo-dextrin. 

Pancreatic  juice  and  intestinal  juice  are  able  to  turn  the  achroo-dextrin  which 
remains  into  maltose,  and  maltose  into  glucose  (dextrose).  It  is  doubtful  whether 
saliva  possesses  the  same  power. 

(2.)  Proteolytic  convert  proteids  into  peptones.  The  nature  of  their 
action  is  probably  hydrolytic.  The  proteolytic  ferments  of  the  body 
are  called  Pepsin,  acting  in  an  acid  medium  from  the  gastric  juice. 
Trypsin,  acting  in  an  alkaline  medium  from  the  pancreatic  juice.  The 
Succus  entericus  is  said  to  contain  a  third  such  ferment. 

(3.)  Inversive,  which  convert  cane  sugar  or  saceluirose  into  grape 
sugar  or  glucose.  Such  a  ferment  was  found  by  Claude  Bernard  in  the 
Succus  entericus  :  and  probably  exists  also  in  the  stomach  mucus. 

2  C12  H2,  On  +  2H.;0  =  C12  H24  012  -f  C12  H2+  012 
Saccharose     "Water  Dextrose       Laevulose 

(4.)   Ferments  which  act   upon  fats,  such  a  body  called  Steapsin,  has 

been  found  in  pancreatic  juice. 

The  ferments  Amylopsin,  Trypsin,  and  Steapsin,  are  said  to  exist  separately  in 
pancreatic  juice,  and  if  so,  make  up  what  was  formerly  called  Panrreatin,  and 
which  was  said  to  have  the  functions  of  the  three. 

(5.)  Milk-curdling  ferments.  It  has  been  long  known  that  rennet,  a 
decoction  of  the  fourth  stomach  of  a  calf,  in  brine,  possessed  the  power 
of  curdling  milk.  This  power  does  nut  depend  upon  the  acidity  of  the 
gastric  juice,  since  the  curdling  will  take  place  in  a  neutral  or  alkaline 
medium;  neither  does  it  depend  upon  the  pepsin,  as  pure  pepsin 
scarcelv  curdles  milk  at  all.  and  the  rennet  which  rapidly  curdles  milk 
has  a  very  feeble  proteolytic  action.  From  this  and  other  evidence  it 
is  believed  that  a  distinct  milk-curdling  ferment  exists  in  the  stomach. 
W.  Roberta  has  shown  that  a  similar  but  distinct  ferment  exist.-  in  pan- 
creatic extract,  which  acts  best  in  an  alkaline  medium,  next  best  in  an 
acid  medium,  and  woist  in  a  neutral  medium.  The  ferment  of  rennet 
acts  best  in  an  acid  medium,  and  worst  in  an  alkaline,  the  reaction 
ceasing  if  the  alkalinitv  be  more  than  slight. 

In  addition  to  the  above  ferments,  many  others  most  likely  exist  in 
the  body,  of  which  the  following  are  the  most  important  : 


AJPPENDIi 


855 


6.  Fibrin-forming  fermenl  (Schmidt),  (see  p.  ■'-  jr.),  found  in 
the  blood,  lymph  and  chyle. 

7.  A  ferment  which  converts  glycogen  into  glucose  in  the  liver;  being 
therefore  an  amylolytic  ferment. 

8.  Urinary  ferments. 

(li.)   Organic   non-nitrogenous  bodies   consist    of — (1.)  Oils    and   I 
(2.)  Amyloids.     (3.)  Acids. 

(1.)  Oils  and  Fats. 
Sapon  inablc.  Non  -saponijiui'fi . 

Palmitin         .         .  CS1 II,,,,  <>,.,       Cliolesterin    .         .         .     C\.„HI4  (» 

Stearin       .         .         .     .     C87  Hn()Oc       Stercoral  .         .     .  1 

Olein       ....     C-.H1()+ou       Excretin  .         .         .    CJgH16oS0a 

( Constitution. 

Tht  Saponifiablt  fats  are  funned  by  the  union  of  fatty  acid  radicals 
with  tlie  triatomic  alcohol,  Glycerin  C3  H.  (OH)3.  The-  radicals  are 
Cl8  H35  O,  Cl6  H,,  0,  and  Cl8  Hr  0,  respectively.  Human  fat  consists 
of  a  mixture  of  palmitin,  stearin,  and  olein,  of  which  the  two  former  con- 
tribute three-quarters  of  the  whole.    Olein  is  the  only  liquid  constituent. 

General  characteristics. — Insoluble  in  water  and  in  cold  alcohol; 
soluble  in  hot  alcohol,  ether,  and  chloroform.  Colourless  and  tasteless; 
easily  decomposed  or  saponified  by  alkalies  or  super-heated  steam  into 
glycerin  and  the  fatty  acids. 

Non-Saponifiable. — Gholesterin,  ( '_,  H44  0,  is  the  only  alcohol  which 
lias  been  found  in  the  "body  in  a  free  state.  It  occurs  in  small  quanti- 
ties in  the  blood  and  various  tissues,  and  forms  the  principal  consti- 
tuent of  gall-stones.  It  is  found  in  dropsical  fluids,  especially  in  the 
contents  of  cysts,  in  disorganised  eyes,  and  in  plants  (especially  peas 
and  beans).  It  is  soluble  in  ether,  chloroform,  or  benzol.  It  crystal- 
lises in  white  feathery  needles.  See  also  under  the  head  of  the  consti- 
tuents of  the  Idle. 

Excretin  (Marcet),  and  Stercorin  (Flint),  are  crystalline  fatty  bodies 
which  have  been  isolated  from  the  faeces. 

(2.)  Amyloids. 

A  in  tjl dill*. — Under  this  head  are  included  both  starch  and  sugar. 
Tlu-  substances,  like  the  fats,  contain  carbon,  hydrogen,  and  oxygen  ; 
but  the  last-named  element  is  present  in  much  larger  relative  amount, 
the  hydrogen  and  oxygen  being  in  the  proportion  to  form  water. 

The  following  varieties  of  these  substances  are  found  in  health  in 
the  body. 

(,/)  Glycogen  (C6  HI0  0.).— This  substance,  which  is  identical  in 
composition  with  starch,  and  like  it,  is  readily  converted  into  sugar  by 
ferments,  is  found  in  many  embryonic  tissues  and  in  all  new  forma- 
tions where  active  cell-growth  is  proceeding.      It  is  present  also  hi  the 


S$6  APPENDIX. 

placenta.     After  birth  it  is  found  almost  exclusively  in  the  liver  and 
muscles. 

Glycogen  is  formed  chiefly  from  the  saccharine  matters  of  the  food  ; 
but  although  its  amount  is  much  increased  when  the  diet  largely  con- 
sists  of  starch  and  sugar,  these  are  not  its  only  source.  It  is  still 
formed  when  the  diet  is  flesh  only,  by  the  decomposition,  probably,  of 
albumin  into  glycogen  and  urea. 

The  destination  of  glycogen  has  been  considered  in  a  former  chapter. 
(See  p.  350.) 

(h)  Glucose  or  grape-sugar  (Ca  HI2  06  +  H2  0)  is  found  in  minute 
quantities  in  the  blood  and  liver,  and  occasionally  in  other  parts  of 
the  body.  It  is  derived  directly  from  the  starches  and  sugars  in  the 
food,  or  from  the  glycogen  which  has  been  formed  in  the  body  from 
these  or  other  matters.  However  formed,  it  is  in  health  quickly  burnt 
off  in  the  blood  by  union  with  oxygen,  and  thus  helps  in  the  mainte- 
nance of  the  body's  temperature.  Like  other  amyloids  it  is  one  source 
whence  fat  is  derived. 

(r)  Lactose  or  sugar  of  milk  (CI2  H22  0„  -f  H2  0),  is  formed  in  large 
quantity  when  the  mammary  glands  are  in  a  condition  of  physiological 
activity, — human  milk  containing  5  or  6  per  cent,  of  it.  Like  other 
sugars  it  is  a  valuable  nutritive  material,  and  hence  is  only  dis- 
charged from  the  body  -when  required  for  the  maintenance  of  the 
offspring.  The  same  remark  is  applicable  to  the  other  organic  nutrient 
constituents  of  the  milk,  albumin  and  saponifiable  fats,  which,  if  we 
except  what  is  present  in  the  secretions  of  the  generative  organs,  are 
discharged  from  the  body  only  under  the  same  conditions  and  in  the 
same  secretion. 

(J)  Inosite  (C6  HI2  06  +  2  H2  0),  a  variety  of  sugar,  identical  in 
composition  with  glucose,  but  differing  in  some  of  its  properties,  is 
found  constantly  in  small  amount  in  muscle,  and  occasionally  in  other 
tissues.  Its  origin  and  uses,  in  the  economy  are,  presumably,  similar 
to  those  of  glycogen. 

(<?)  Maltose  (CI2  H22  0„),  is  formed  in  the  conversion  of  starch  into 
glucose  (see  p.  853). 

•(3)  Organic  Acids. 

Group  I. — Monatomic  Fatty  Acids. 

Formic  .         .         .     C   HO     OH       Caproic      .         .         .  C,.   Hu  0  OH 

Acetic      .         .         .     .     C2  H3  0  OH        Capric Cs   H15  0  OH 

.  C1(.  H31  0  OH 

•         •     •  C18H350  0H 

.  Cia  H„  0  OH 


Propionic 
Butyric  . 
Valerianic 


c 

HO     OH 

Caproic 

C, 

H30  OH 

Capric  . 

C3 

H",  0  OH 

Palmitic 

c, 

H.  OOH 

Stearic 

c5 

HgOOH 

Oleic 

Formic,  acetic,  and  propionic  acids  are  present  in  sweat,  but  normally 
in  no  other  human  secretion.  They  have  been  found  elsewhere  in 
diseased  conditions.      Butyric  acid  is  found  in  sweat.      Various  others 


APPENDIX. 


857 


<>l'  these  acids  Lave  been  obtained   from  blood,  muscular  juice,  I 
and  urine. 

Gnoup  1 1.     Diatomic  I'm  i  v  Acids. 


Monobasic. 

Ulycoli.  .  .  .  .  (',  IT,  <>, 
Lactic  .  .  ..<'..  11,.,  ( > 3 
Leucic      ....     Ca  II ,._.  0a 


Bibaric, 

Oxalic    .        .        .        .  <\    11 1  04 

Succinic     .        .        .     .  <\    II 

Sebacic  ....  (',,,  II,',  04 


Lactic  acid  exists  in  a  free  state  in  muscular  plasma,  and  is  in- 
creased in  quantity  by  muscular  contraction,  is  neveT  contained  in 
healthy  blood,  and  when  present  in  abnormal  amount  seems  to  produce 
rheumatism. 

Oxalates  are  presenl  in  the  urine  in  certain  diseases,  and  after  drink- 
ing certain  carbonated  beverages,  and  after  eating  rhubarb,  &c. 

Aromatic  Seeies. 

Benzoic  ......     CT  II,.  <  >„ 

Phenol CaH00~ 

Benzoic  arid  is  always  found  in  the  urine  of  herbivora,  and  can  be 
obtained  from  stale  human  urine.     It  does  not  exisl  free  elsewhere. 

Phenol.  —  Phenyl  alcohol  or  carbolic  acid  exists  in  minute  quantity  in 
human  urine.      ]t  is  an  alcohol  of  the  aromatic  series. 


2.  Inorganic  Principles. 

The  inorganic  proximate  principles  of  the  human  body  are  numerous. 
They  are  derived,  for  the  most  part,  directly  from  food  and  drink,  and 
pass  through  the  system  unaltered.  Some  are,  however,  decomposed 
on  their  way,  as  chloride  of  sodium,  of  which  only  four-fifths  of  the 
quantity  ingested  are  excreted  in  the  same  form  ;  and  some  are  newly 
formed  within  the  body, — as  for  example,  a  part  of  the  sulphates  and 
carbonates,  and  some  of  the  water. 

Much  of  the  inorganic  saline  matter  found  in  the  body  is  a  necessary 
constituent  of  its  structure, — as  necessary  in  its  way  as  albumin  or  any 
other  organic  principle  ;  another  part  is  important  in  regulating  or 
modifying  various  physical  processes,  as  absorption,  solution,  and  the 
like  ;  while  a  part  must  be  reckoned  only  as  matter,  which  i 
to  speak,  accidentally  present,  whether  derived  from  the  food  or  the 
tissues,  and  which  will,  at  the  first  opportunity,  be  excreted  from  the 
body. 

Gases. — The  gaseous  matters  found  in  the  body  are  Oxygen,  "Hy- 
drogen, Nitrogen,  Carburetted  and  Sulphuretted  hydrogen,  and  Carbonic 
acid.  The  first  three  have  been  referred  to  (p.  843).  Carburetted 
and  sulphuretted  hydrogen  are  found  in  the  intestinal  canal.      Carbonic 


858  APPENDIX. 

acid  is  present  in  the  blood  and  other  fluids,  and  is  excreted  in  large 
quantities  by  the  lungs,  and  in  very  minute  amount  by  the  skin.  It 
will  he  specially  considered  in  the  chapter  on  Respiration. 

Water,  the  most  abundant  of  the  proximate  principles,  forms  a 
large  proportion, — more  than  two-thirds  of  the  weight  of  the  whole 
body.  Its  relative  amount  in  some  of  the  principal  solids  and  fluids 
of  the  body  is  shown  in  the  following  table  (quoted  by  Dalton,  from 
Robin  and  Yerdeil's  table,  compiled  from  various  authors)  : — 


Quantity  of  "Water  in  iooo  Parts. 


100 

Bile           .... 

880 

130 

Milk 

.     887 

550 

Pancreatic  juice 

900 

750 

Urine  ..... 

936 

768 

Lymph      .... 

960 

789 

Gastric  juice 

975 

795 

Perspiration      . 

986 

805 

Saliva ..... 

995 

Teeth 
Bones  . 
Cartilage  , 
Muscles 

Ligament 
Brain  . 
Blood 

Synovia 


Uses  of  the  Water  of  the  Body. — The  importance  of  water  as 
a  constituent  of  the  animal  body  may  be  assumed  from  the  preceding 

table,  and  is  shown  in  a  still  more  striking  manner  by  its  withdrawal. 
If  any  tissue, — as  muscle,  cartilage,  or  tendon  be  subjected  to  heat 
sufficient  to  drive  off  the  greater  part  of  its  water,  all  its  characteristic 
physical  properties  are  destroyed  ;  and  what  was  previously  soft, 
elastic,  and  flexible,  becomes  hard  and  brittle,  and  horny,  so  as  to  be 
scarcely  recognisable. 

In  all  the  fluids  of  the  body — blood,  lymph,  &c,  water  acts  the 
part  of  a  general  solvent,  and  by  its  means  alone  circulation  of  nutrient 
matter  is  possible.  It  is  the  medium  also  in  which  all  fluid  and  solid 
aliments  are  dissolved  before  absorption,  as  well  as  the  means  by  which 
all,  except  gaseous,  excretory  products  are  removed.  All  the  various 
processes  of  secretion,  transudation,  and  nutrition,  depend  of  necessity 
on  its  presence  for  their  performance. 

Source. — The  greater  part,  by  far,  of  the  water  present  in  the  body 
is  taken  into  it  as  such  from  without,  in  the  food  and  drink.  A  small 
amount,  however,  is  the  result  of  the  chemical  union  of  hydrogen 
with  oxygen  in  the  blood  and  tis.sues.  The  total  amount  taken  into 
the  body  every  day  is  about  4^  lbs.  ;  while  an  uncertainty  quantity 
(perhaps  1  to  |  lb.)  is  formed  by  chemical  action  within  it. — 
(Dalton.) 

IiOSS. — The  loss  of  water  from  the  body  is  intimately  connected 
with  excretion  from  the  lungs,  skin,  and  kidneys,  and,  to  a  less 
extent,  from  the  alimentary  canal.  The  loss  from  these  various 
organs  may  be  thus  apportioned  (quoted  by  Dalton  from  various 
observers). 


APPENDIX.  859 


Proa  the  Aliim utary  Canal  (i 

,,        Lai 

Skin  (perspiration) 

Kidneys    mine)  . 


4P« 

it  cent. 

20 

>» 

30 

>  > 

46 

ri 

100 

Sodium  and  Potassium  Chlorides  are  present  in  marly  all 
parts  of  the  body.  Tin-  former  seems  to  1"-  especially  necessary, 
judging  from  the  instinctive  craving  foi  it  on  tin*  part  of  animal-  in 
whose  food  it  is  deficient,  and  from  the  diseased  condition  which  is 
consequent  on  its  withdrawal  In  the  blood,  the  quantity  of  chloride 
of  Bodium  is  greater  than  that  of  all  its  other  saline  ingredients  taken 
together.  In  the  muscles,  on  the  other  hand,  the  quantity  of  chloride 
of  sodium  is  less  than  that  of  the  chloride  of  potassium. 

Calcium  Fluoride,  in  minute  amount,  is  present  in  the  bones 
and  teeth,  and  traces  have  been  found  in  the  blood  and  Borne  other 
fluids. 

Calcium,  Potassium,  Sodium,  and  Magnesium  Phosphates 
are  found  in  nearly  every  tissue  and  fluid.  In  some  tissues — the  bones 
and  teeth.— the  phosphate  of  calcium  exists  in  very  large  amount,  and  is 
the  principal  source  of  that  hardness  of  texture,  on  which  the  proper 
performance  of  their  functions  so  much  depends.  The  phosphate  of 
calcium  is  intimately  incorporated  with  the  organic  basis  01  matrix, 
but  it  can  be  removed  by  acids  without  destroying  the  general  shape 
of  the  hone  ;  and,  after  the  removal  of  its  inorganic  salts,  a  hone  is 
left  soft,  tough,  and  flexible. 

Potassium  and  sodium  phosphates  with  the  carbonates,  maintain  the 
alkalinity  of  the  blood. 

Calcium  Carbonate  occurs   in    bones   and   teeth,   but   in   much 

smaller  quantity  than  the  phosphate.      It  is  found  also  in  some  other 

parts.      The  small   concretions  of  the  internal    ear  (otoliths)  are  com- 

1  of  crystalline  carbonate  of  calcium,  and   form  the  only  example 

of  inorganic  crystalline  matter  existing  as  such  in  the  body. 

Potassium  and  Sodium  Carbonates  are  found  in  the  blood, 
and  -nme  other  fluids  and  tissues, 

Potassium,  Sodium,  and  Calcium  Sulphates  are  met  with 
in  small  amount  in  most  of  the  solids  and  fluids. 

Silicon. — A  very  minute  quantity  of  siliea  exists  in  the  urine,  and 
in  the  blood.  Traces  of  it  have  been  found  also  in  bones,  hair,  and 
some  other  part-. 

Iron. — The  especial  place  of  iron  is  in  haemoglobin,  the  colouring- 
matter  of  the  blood,  of  which  a  further  account  has  been  given  with 
the  chemistry  of  the  blood.  Peroxide  of  iron  is  found,  in  very  small 
quantities,  in  the  ashes  of  bones,  muscles,  and  many  tissues,  and  in 
lymph    and    chyle,  albumin  of  serum,  fibrin,    bile,   and  other   fluids  ; 


86o  APPENDIX. 

and   a   salt   of  iron,   probably  a  phosphate,  exists  in   the   hair,  black 
pigment,  and  other  deeply  coloured  epithelial  or  horny  substances. 

Aluminium,  Manganese,  Copper,  and  Lead. — It  seem, 
most  likely  that  in  the  human  body,  copyer,  manganesium,  ahitniniwrn 
and  lead  are  merely  accidental  elements,  which,  being  taken  in  minute 
quantities  "with  the  food,  and  not  excreted  at  once  with  the  faxes,  are 
absorbed  and  deposited  in  some  tissue  or  organ,  of  which,  however, 
they  form  no  necessary  part.  In  the  same  manner,  arsenic,  being 
absorbed,  may  he  deposited  in  the  liver  and  other  parts. 


APPENDIX    B. 


MEASURES   OP   WEIGHT   {Avoirdupou). 
(J  cerages.) 


lbs. 

<'ZS. 

Ri   «iit  Skeleton 

21 

8 

M  ii- 

;  and  Tendons   .    . 

77 

8 

Skin    and     Subcutaneous 

tissue     .... 

16 

5 

Blood 

.      .    II  to 

14 

forum    . 

J  Cerebellum     .     . 

2 

12 

Brain 

- 

51 

J  Pons  and  Medulla 
*     oblongata    .     . 

Encepbalon    .     . 

- 

1 

3 

A 

- 

1 

Heart 

. 

- 

IO 

ines,  small 

1 

11$ 

j? 

large   .         .     . 

1 

I 

Kidney 

3  (both) 

- 

10J 

Larynx 

Trachea.and  larger 

Bronchi 

- 

lbs. 


Liver  . 

Lungs  (both)  . 
(Esophagus 

Ovaries  (both) 
Pancreas      .... 
Salivary  Glands  (both  sides), 
i\  to 
Stomach  .         .         .     . 

Spinal  Cord,  divested  of  its 
nerves  and  membiani  - 

Spleen 

Suprarenal  Capsules  (both), 

LtO 

Testicles  (both)     .      H  to 
Thyroid  body  and  remains 

of  Thymus  gland     . 
Tongue  ami  Hyoid  bone 
Uterus  (virgin)    .         .  h  to 


MEASURES    OF   LENGTH  {Average). 


.    2 
to    - 


10 


if 


2 

7 

7 


2 


ft. 

in. 

ft. 

in. 

Appendix  vermiformis  3  to 

6 

Ligament  of  ovary 

- 

1^ 

Bronchus,  right    . 

.     - 

\h 

Meatus  auditorius  externus  . 

- 

M 

'  left 

.     - 

2h 

Medulla  oblongata 

- 

ij 

Caecum 

.     - 

zi 

(Esophagus   . 

- 

10 

Duct,  common  bile  . 

.     - 

3 

Pancreas  .         .         .         .     . 

- 

7 

ejaculatory,f 

to- 

I 

Pharynx        . 

- 

4i 

of  Cowper's  gland 

- 

l\ 

Rectum     .                 .         .     . 

- 

8 

liepatic  . 

.    - 

2 

Spinal  cord   .         .         .         . 

1 

5 

nasal  . 

.    - 

a 

~4 

Tabulus  seminiferus         .     . 

2 

.,      parotid    . 

- 

2h 

Urethra,  male 

- 

8 

sub-maxillary 

- 

2] 

female         .         .     . 

- 

l| 

Epididymis 

- 

15 

Ureter  .         .         .         .         . 

1 

4 

,.          unravelled 

20 

- 

Vagina      .         .                 4  to 

- 

6 

Eustachian  tube 

- 

I* 

Vas  deferens 

2 

_ 

Fallopian  tube 

- 

3^ 

yesicula  Beminalis    .        .    . 

- 

2 

Intestine,  large         .         .  5 

to  6 

- 

„           .,  unravelled,  4  to 

- 

6 

„         small     . 

20 

- 

Vocal  cord    .... 

- 

_i_ 

Ligament,  round,  of  uterus  . 

- 

4i 

862 


APPENDIX. 


SIZES   OF   VARIOUS   HISTOLOGICAL   ELEMENTS  AND    TISSUES. 
Average  she  infractions  of  an  inch. 


Air-eells.  £  to  ±. 

Blood-cells  (red).  ^  (breadth). 
„     -ijjj  (thickness). 
„      (colourless),  ^33. 
Canaliculus  of  bone,  ^  (width). 
Capillary  blood-vessels,  ^  (lung)  to 

1^5  One). 
Cartilage-cells  (nuclei  of),  ^. 
Chyle-molecules,  35^. 
Cilia.  ^  to  zko  (length). 
Cones  of  retina  (at  yellow  spot).  y^ 

to  safes  (width). 
Connective-tissue  fibrils,  ^^  to  j£uo 

(width). 
Dentine-tubules,  ^  (width). 
Enamel-fibres.  ^  (width). 
End-bulbs,  g*g. 
Epithelium 

columnar  (intestine),  ^  (length). 

spheroidal  (hepatic),  ^  to  ^. 

squamous  (peritoneum)IDijj0(width). 
„  (mouth),     gjL         „ 

(skin),       Jjj 
Elastic  (yel.)  fibres,  ^to^  (wide). 
Fat-cells,  &.  to  ^ 
Germinal  vesicle,  Ti0. 

,,  Spot,  3^35. 

Glands 

gastric,  &  to  i  (length). 
„     5^3  to  ^  (width). 
Lieberkuhn's  (small  intestines),  ^ 

to  sis  (length). 
Lieberkuhn's  (small  intestine),  ^ 

(width). 
Peyer's  (follicles),  ^toi. 
Sweat,  i  (width). 

.,     in  axilla.  A  to  1  (width). 


Haversian  canals,  ^  to  ^  (width). 
Lacunae  (bone),  ^  (length). 
sax,  (width). 

Macula  lutea,  ^j. 

Malpighian  bodies  (kidney),  ^ 

corpuscles'(spleen).itoi. 
Muscle  (striated).  ^  to  ^  (width). 
, ,     -cell  (plain) .  ni-  to  ^  (length). 

»        THx3  tO  gig  (Width). 

Nerve -corpuscles  (brain),  3^  to  gL. 
„     -fibres  (medullated)  p^  to  ^J^ 
(width), 
(non-medullated)  g^  to 
S&Q  (width). 
Ovum,  jig. 

Pacinian  bodies,  ^to  i.  (length). 

.,  n      ^toi  (width). 

Papillae   of    skin   (palm),  ^  to  ^ 

(length). 

„         „     (face).  ^  to  ^     „ 

„        tongue  (circumvallate),  ^-, 

to  i  (width). 
„         .,  (fungiform),  £  to  g| 

(width). 
,,         „  (filiform),i(length). 

Pigment-cells  of  choroid  (hexagonal), 
i 

lOOO* 

„         granules,  g^. 
Spermatozoon,  ^tOgfe  (length). 
».  head.  ^ 

n  »     10DO0  (width). 

Touch-corpuscle,  ^  (length). 
Tubuli  seminiferi,  t^to^  (width). 

„      uriniferi.^. 
Villi,  i  to  ^(length). 
„    J  to  x  (width). 


APPENDIX. 


863 


SPECIFIC   GRAVITY   OP   VARIOUS    FLUIDS    AND   TISSUES. 


{Water 

=  rooo.) 

Adipose  1  issue 

.    0932 

Liver          .... 

'•055 

Bile 

1020 

Lymph   .... 

1  020 

Blood  .... 

1055 

Lungs 

corpuscles  (red )    . 

I-oSS 

when  fully  distended     . 

01 26 

Body  (entire) 

1065 

ordinary    condition,     posi 

Bone        .        .        .    1S70 

to  1 '970 

mortem    .        .     0-345 

to  0*746 

Brain   .... 

1-036 

when  deprived  of  air    . 

1  -056 

..    grey  matter    . 

1034 

Muscle  .... 

1  020 

..    white  . 

1040 

Milk           .... 

1  030 

Cartila 

1-150 

Pancreatic  juice     . 

IOI2 

'  lerebro-spinal  fluid 

1006 

Saliva         .... 

IOO6 

Chyle       .... 

1  024 

Serum    .... 

I026 

<  tastric  juice 

1  0023 

Spleen         .... 

IO60 

Intestinal  juice 

ion 

Sweat     .... 

I.OO4 

Kidney 

1-052 

Urine          .... 

I020 

Liquor  amnii  . 

i'oo8 

TABLE   SHOWING  THE  PERCENTAGE  COMPOSITION 

VARIOUS   ARTICLES    OF   FOOD.     (Letheby.) 


OF 


Water. 

Albumin. 

Starch. 

Sugar. 

Fat. 

.Salts. 

15  read 

•     37     •• 

.        81      ... 

47-4     ... 

3-6     • 

r6     . 

•■       2'3 

Oatmeal 

.   15   .. 

126     ... 

58-4     .- 

5'4     • 

•       5-6     • 

..     3" 

Indian  corn  meal 

.    14    .. 

ill      ... 

647     ». 

0-4     . 

.       8-i     . 

•  •     17 

Rice 

•    13   •• 

6-3     -. 

791      ... 

0-4     . 

0-7     . 

••     o'5 

Arrowroot  . 

.    18    .. 

— 

82'         ... 

— 

— 

— 

Potat 

•     75     •• 

21 

18-8     ... 

3-2     .. 

0-2 

•     0-7 

Carrots 

•     S3     .. 

13     ... 

8-4     ... 

6-i     .. 

0*2      . 

10 

Turnips 

.     91     .. 

1*2      ... 

51     ... 

2'I       .. 

— 

.     o-6 

Sugar 

5     .« 

— 

— 

95'°     • 

— ■ 

— 

Treacle  . 

23     ... 

— 

— 

770     .. 

— 

.      — 

Milk  . 

86     ... 

4-1     ... 

— 

5'2       •■ 

•       3"9     • 

.     08 

Cream    . 

66     ... 

27     ... 

— 

2-8     .. 

26-7 

.     r8 

Cheddar  cheese 

36     ... 

28-4     ... 

— 

— 

.     311     . 

•     4'5 

Lean  beef 

72     ... 

193     ... 

— 

— 

•       3-6     - 

•     5* 

Fat  beef    .        .     . 

51     .» 

14-8     ... 

— 

— 

.     29-8     .. 

•     4'4 

Lean  mutton 

72     ... 

I8'3     -. 

— 

— 

4'9     • 

.     4-8 

Fat  mutton    . 

53     ■•• 

12-4     ... 

— 

— 

.     311     •• 

•     3"5 

Veal                      .     . 

63     ... 

16-5     ... 

— 

— 

.     158     . 

•     47 

Fat  pork 

39     •  •• 

98     ... 

— 

— 

.     48-9     • 

•     23 

Poultry      .         .     . 

74     ••• 

210     ... 

— 

— 

.       38     .. 

.       1*2 

White  Fish     . 

78     ... 

181     ... 

— 

— 

.       2-9     .. 

.       I'O 

Eels  . 

75     ... 

9-9     ... 

— 

— 

.    iy8   :. 

•     1*3 

Salmon  . 

77     .- 

16-1     ... 

— 

— 

5-5   •• 

•     1 '4 

White  of  egg    .    . 

78     ... 

20*4     . . . 

—      ... 

— 

— 

.     r6 

Yelk  of  egg   . 

52     ... 

160     ... 

— 

— 

307   •• 

•     1*3 

Butter  and  Fat 

15     ... 

— 

— 

— 

.   83-0   .. 

.       2*0 

Beer  and  porter    . 

91     ... 

01     ... 

— 

87    .. 

— 

02 

S6+ 


APPENDIX. 


CLASSIFICATION    OF    THE    ANIMAL    KINGDOM. 


Mammalia 

Primates 

Chiroptera     . 
Insectivora 
Carnivora     . 
Proboscidea 
Hyracoidea  . 
Ungulata  : 
Perissodactyla 
Artwdactyla   . 

Sirenia    . 

Cetacea 
Eodentia 

Edentata 

Marsupiata 

Monotremata 

Birds 


VEETEBKATA. 

Typical  Examples. 

.  Man. 

,     .  Ape,  baboon. 

.  P>at.  flying  fox. 

.     .  Mole,  nedgeb  _. 

.  Lion,  dog,  bear.  seal. 

.     .  Elephant. 

.  Hyrax. 

,     .     Tapir,  rhinoceros,  horse. 

.     Hippopotamus.    pig,    camel,    chevrotain, 
deer,  ox,  sheep,  goat,  giraffe. 
,     .     Dugong.  manatee. 

.     Whale,  porpoise,  narwhal. 
.     .     Hare,  porcupine,  guinea  pig.  rat,  beaver, 
squirrel,  dormouse. 
.     Armadillo,  pangolin,  true  anteater.  Cape 
anteater,  sloth. 
.     .     Opossum,     bandicoot,     Thylacinus.    pha 
langer,  wombat,  kangaroo. 
.     Ornithorhynchus  or  duck-billed  platypus, 
Echidna  or  spiny  anteater. 


Cartnatje 

Eaptores  (Birds  of  prey")  < 
Scansores  (Climbing  Birds) 
Passeres  (Perching  Birds')  . 

Easores  (Scratching  Birds')  . 
Grallatores  {Wading  Birds) 
Xatatores  {Swimming  Birds) 

Eatit.e 

Cursores  (Running  Birds)  . 

Eeptiles 

Crocodilia  .         .         .     . 

Lacertilia       . 

Chelonia  .  .  .  .  . 
Ophidia  .... 

Amphibia 

Anura  .  .  ... 
Urodela  .... 

Fish  • 

Dipnoi       .         .'        . 

Teleostei 

Placoidei  .**."".    •  ■ . 

Canoidei 

Gyclostomi         .         .... 

Leptocardii  . 


Vulture,  hawk,  owl. 
Woodpecker,  parrot. 
Crow,  finch,  swallow. 
Fowl,  pheasant,  grouse. 
Heron,  stork,  snipe,  crane. 
Penguin,  duck,  pelican,  guU. 


Ostrich,  emeu,  apteryx. 

Crocodile,  alligator. 

Iguana,  chameleon,  gecko,  lizard,   slow- 
worm,  flying  dragon. 
Tortoise,  turtle. 
.■snake,  viper. 

Frog.  toad. 
Newt,  salamander. 


Lepidosiren. 

Perch,  mackerel,  cod,  herring. 

Shark,  ray. 

Sturgeon,  bony  pike. 

Lamprey,  hag. 

Amphioxus  lanceolatus. 


APPENDIX. 


865 


CLASSIFICATION    OF    THE    ANIMAL     KINGDOM. 


IXVEUTEIillATA. 


MOLLU8CA 

Cephalopoda    . 

Pteropoda    . 
<  laateropoda  : 

Pulmonigasteropoda    . 

Branchiogasteropoda 
Lamellibranchiata  . 
Brachiopoda 

Tunicata,  or  Ascidioidea. 
Bryozoa  or  Polyzoa 

Arthropoda 
Insecta    . 


Araehnida 
Myriopoda 
Crustacea 


Typical  Examples. 
argonaut,    squid,     cuttle-fish 


Octopus 

nautilus 

Clio,  Cleodora, 

Snail,  slug. 

Whelk,  limpet,  periwinkle. 
<  ►yster,  mussel,  cockle. 
Terebratula,  Lingula. 

Salpa,  Pyrosoma. 
Sea  mat. 


Beetle,  bee,  ant,  locust,  grasshopper,  cock- 
roach, earwig,  moth,  butterfly,  fly,  flea. 

bug. 
Scorpion,  spider,  mite. 
Centipede,  millipede. 
Crab,  lobster,  crayfish,  prawn,  barnacle. 


Annulata 
Scolecida 

Echinodermata 


CCELEXTERATA 
Ctenophora 
Anthozoa 
Hydrozoa 

Spongida 

Protozoa 

Khizopoda 
Infusoria 


Sea-mouse,  leech,  earthworm. 

Hair-worm,  thread-worm,  round-worm, 
fluke,  tape-worm,  guinea-worm. 

Sea-cucumber,  sea-urchin,  star-fish,  sand- 
star,  feather-star. 


Beroe. 

Sea  anemone,  coral,  sea-pen. 

Hydra,    Sertularia,    Velella, 

man-of-war. 
Sponge-. 


Foraminifera.  Amoeba. 
Paramcecium.  Vorticella. 


Portuguese 


3  K 


INDEX. 


A. 


Abdominal  muscles,  action  of  in  respira- 
tion, 232 
Aberration, 

chromatic,  711 

spherical,  710 
Abomasum,  296 
Absorbents.     See  Lymphatics. 
Absorption,  361 

by  blood-vessels,  377 

by  lacteal  vessels,  375 

by  lymphatics,  376 

conditions  for,  380 

by  the  skin,  426 

oxygen  by  lungs,  241 

process  of  osmosis,  378 

rapidity  of,  379 

See  Chyle,  Lymph,  Lymphatics,  Lac- 
teals. 
Accessor)'  nerve,  635 
Accidental  elements  in  human  body,  860 
Accommodation  of  eye,  703 
Acids,  organic,  856 

acetic,  ib. 
Acid-albumin,  305,  846 
Acini  of  secreting  glands,  399 
Actinic  rays,  724 
Addison's  disease,  471 
Adenoid  tissue,  40 
Adipose  tissue,  42.     See  Fat. 

development,  44 

situations  of,  ib. 

structure  of,  ib. 
Adrenals,  469 
After- birth,  778 
After-sensations, 

taste,  666 

touch,  658 

vision,  715 
Aggregate  glands,  399 
Agminate  glands,  319 
Air, 

atmospheric,  composition  of,  238 

breathing,  234 

complemental,  ib. 

reserve,  ib. 


Amides. 

Air,  continued. 

residual,  234 

tidal,  ib. 

changes  by  breathing,  239 

quantity  breathed,  235 

transmission  of    sonorous    vibrations 
through,  679,  680 

in  tympanum,  for  hearing,  682 

undulations  of,  conducted  by  external 
ear,  679,  680 
Air-cells,  224 

Air-tubes,  220.     See  Bronchi. 
Alanines,  848 
Albino-rabbits,  24 
Albumin,  845 

acid,  305 

action  of  gastric  fluid  on,  ib. 
alkali,  845,  846 

characters  of,  ib. 

chemical  composition  of,  845 

derived,  846 

egg,  845 

native,  ib. 

serum,  106,  845  .  . 

tissues   and    secretion    in    which    it 
e.xists,  ib. 

of  blood,  102 
Albuminoids,  845 
Albuminose,  847 
Albuminous  substances, 

absorption  of,  354 

action  of  gastric  fluid  on,  305 
of  liver  on,  348 
of  pancreas  on,  330 
Alcoholic  drinks,  effect  on  respiratory 

changes,  240 
Alimentary  canal,  277 

development  of,  806 

length  in  different  animals,  352 
Allantoin,  851 
Allan tois,  769,  7 70 
Alloxan,  851 
Aluminium,  860 
Amic  acids,  848 
Amides,  ib. 

3  K  2 


863 


IXDEX. 


Ammonia. 

Ammonia, 

cyanate    of,    identical    with     urea, 
'  442,  850 

exhaled  from  lungs,  242 

urate  of,  444 
Amnion,  769 

fluid  of,  770 
Amoeba,  8 
Amoeboid  movements,  9,  475 

cells,  35 

colourless  corpuscles,  99 

cornea-cells,  34 

ovum,  758 

protoplasm,  8 

Tradescantia,  ib. 
Amphioxus,  779 
Ampulla,  675 

Amputation,  sensations  after,  556 
Amyloids  or  Starches,  855 

action    of    pancreas    and     intestinal 
glands,  331,  352 
of  saliva  on,  285 
Amylopsin,  331,  8s3 
Anacrotic  wave,  182 
Anastomoses  of  muscular  fibres  of  heart, 

T  ->  *> 

of  nerves,  546 

of  veins,  201 

in  erectile  tissues,  210 
Anelectrotonus,  516 
Angle,  optical,  720 
Angulus  opticus  seu  visorius,  ib. 
Animal  heat,  382.     See  Heat  and  Tem- 
perature. 
Animals,  distinctive  characters,  3 
Antialbumate,  847 
Antialbumose,  ib. 
Antihelix,  672 
Antipeptone,  847 
Antitragus,  672 
Anus,  276 
Aorta,  159 

development,  791 

pressure  of  blood  in,  189 

valves  of,  136 
action  of,  141 
Aphasia,  612 

Apnoea,  258.     See  Asphyxia. 
Appendices  epiploic*,  325 
Appendix  vermiformis,  ib. 
Aquaeductus, 

cochlea?,  676 

vestibuli,  675 
Aqueous  humour,  700 
Arches,  visceral,  782 
Area  germinativa,  761 

opaca,  762 

pellucida,  ib. 

vasculosa,  768 
Areolar    tissue,    3 

Tissue. 
Arsenic,  860 
Arterial  tension,  tS 


See    Conned  ive 


Basemext-membrane. 

Arteries,  159 

circulation  in,  171 

velocity  of,  204 
distribution,  159 
muscular  contraction  of,  175 
effect  of  cold  on,  176 

of  division,  ib. 
elasticity,  172 

purposes  of,  ib. 
muscularity,  160 

governed  by  nervous  system,  19a 

purposes  of,  175 
nerves  of,  164 

nervous  system,  influence  of,  190 
office  of,  ib. 

pressure  of  blood  in,  185 
pulse,  177.     See  Pulse. 
rhythmic  contraction,  174 
structure,  160 

distinctions  in  large  and  small  ar- 
teries, ib. 
systemic,  126 
tone  of,  190 
umbilical,  793 
velocity  of  blood  in,  204 
Articulate  sounds,  classification  of,  530. 

See  Towels  and  Consonants. 
Arytenoid  cartilages,  521 

effect  of  approximation,  523 

movements  of,  ib. 
muscle,  521 
Asphyxia,  259 

causes  of  death  in,  ib. 
experiments  on,  260 
Astigmatism,  710 
Atmospheric  ah-,  238.     See  Air. 
pressure  in    relation    to   respiration. 

239 
Auditory  canal,  672 

function,  679 
Auditory  nerve,  678 

distribution,  ib. 

effects  of  irritation  of,  690 
Auricle  of  ear,  672 
Auricles  of  heart,  128,  130 

action,  137 

capacity,  132 

development,  789 

dilatation,  153 

force  of  contraction,  ib. 
Automatic  action,  563, 

cerebrum,  608 

medulla  oblongata,  588 

respiratory,  588,  589 
Axis-cylinder  of  nerve-fibre,  542 


B. 


Barytone  voice,  527 

Basement-membrane, 

of  mucous  membranes,  397 
of  secreting  membranes,  394 


INDEX. 


869 


BA88   VOH  B. 

.  526 

Battery,  DanielT  8,490 

id,  458 
spid  v:i!\.',  1  je 
Bile,  3 
antiseptic  power,  347 
colouring  matter,  340 
composition  of,  338 
digestive  properties,  346 

rementitious,  343 
fat  made  capable  of  absorption  bv, 

tunctions  in  digestion,  tb. 
mixture  with  chyme,  347 

mucus  in,  341 

natural  purgative,  347 

process  of  secretion  of,  342 

quantity,  343 

re-absorption,  342,  347 

salts,  339 

secretion  and  flow,  342 

Becretion  in  foetus,  344 

tests  for,  340,  341 

uses,  343 
Bilifulvm,    Biliprasin,  Bilirubin,   Bili- 

verdin,  340 
Bilin,  339 

preparation  of,  339 


re-absorption  of,  342,  347 
Bioplasm,  6.  See  Protopla 
Birth.  I 


See  Protoplasm 

See   Urinary 


Bladder,   urinary,    430 

Bladder 
Blastema,  6.     See  Protoplasm 
Blastodermic  membrane,  760 
Bleeding,  eft'ects  of,  on  blood,  107 
Blind  spot,  713 
Blood,  78 
albumin,  106 

use  of,  123 
arterial  and  venous,  108 
assimilation,  123 
bufl'y  coat,  82 
chemical  composition,  102 
coagulation,  80 
colour,  78,  108 

changed  by  respiration,  245 
colouring  matter,  103,  112 
colouring  matter,  relation  to  that  of 

bile,  341 
composition,  chemical,  102 

variations  in,  108 
corpuscles  or  cells  of,  92.     See  Blood- 
corpuscles. 

red,  92 

white,  98 
crystals,  1 12 
cupped  clot,  82 
development,  119 
extractive  matters,  105 
fatty  matters,  ib. 

use  of,  123 
fibrin,  81,  104 


Bone. 

Blood,  ru,,t', , ,n,  ,/. 

separation  <><',  81 

use  <>(',  123 
formation  in  liver,  102 

in  Bpleen,  4^4 
i  of,  109 
uaBmoglobin  ororuorin,  103,  112 
hepatic,  108 
menstrual,  743 
odour  or  halitus  of,  '  - 
portal,  characters  of,  108 

purification  of  by  liver,  343 
quantity,  79 
reaction,  78 

relation  of,  to  lymph,  374 
saline  constituents,  106 

uses  of,  124 
serum  of,  105 

compared  with  secretion  of  serous 
membrane,  395 
specific  gravity,  78 
splenic,  108 

structural  composition,  92 
temperature,  78 
uses,  123 

of  various  constituents,  ib. 
variations    of,    in    different    circum- 
stances, 107 

in  different  parts  of  body,  108 
Blood-corpuscles,  red,  92 
action  of  reagents  on,  94 
chemical  composition,  103 
development,  119,  120 
disintegration  and  removal,  122 
method  of  counting,  100 
rouleaux,  94 
sinking  of,  82 
specific  gravity,  93 
stroma,  ib. 

tendency  to  adhere,  94 
uses,  124 
varieties,  93 
vertebrate,  various,  95 
Blood-corpuscles,  white,  98 
amccboid  movements  of,  99 
derivation  of,  122 
formation  of,  in  spleen,  122,  464 
locomotion,  99 
Blood-crystals,  112 
Blood-pressure,  185 
influence  of  vaso-motor  system  of,  193 
variations,  189 
Blood-vessels, 

absorption  by,  377 

circumstances  influencing,  380 

difference   from  lymphatic  absorp- 
tion, 378 

osmotic  character  of,  379 

rapidity  of,  ib. 
development,  786 

influence  of  nervous  system  on,  190 
relation  to  secretion,  403 
Bone,  5 1 


8;o 


IXDEX. 


Boxe. 

Bone,  continued. 

canaliculi,  53 

cancellous,  51 

chemical  composition,  ib. 

compact,  ib. 

development,  57 

functions,  67 

Haversian  canals,  54 

lacuna?,  53 

lamella?,  55 

medullary  canal,  5 1 

periosteum,  52 

structure,  51 

growth,  60 
Brain.       See     Cerebellum,    Cerebrum, 
Pons,  etc. 

adult,  607 

amphibia,  606 

apes,  607 

birds,  606 

capillaries  of,  167,  208 

child,  607 

circulation  of  blood  in,  208,  ct  seq. 

convolutions,  601 

development,  799 

female,  607 

fish,  606 

gorilla,  607 

idiots,  ib. 

lobes,  601 

male,  607 

mammalia,  606 

orang,  608 

proportion  of  water  in,  858 

quantity  of  blood  in,  208,  et  seq. 

rabbit,  607 

reptiles,  606 

weight,  607 
relative,  ib. 
Breathing,  214.     See  Bespiration. 
Breathing-air,  234 
Bronchi,  arrangement  and  structure  of, 

220 
Bronchial  arteries  and  veins,  226 
Brownian  movement,  8 
Brunner's  glands,  318 
Buffy  coat,  formation  of,  81 
Bulbus  arteriosus,  790 
Burdach's  column,  572 
Bursa?  mucosa?,  395 


C. 

Ca?cum,  325 

Calcification  compared  with  ossification, 

62 
Calcium,  859 

fluoride,  ib. 

phosphate,  ib. 

carbonate,  ib. 


Cartilage. 

Calculi,  biliary,  containing  cholesterin, 

855,  . 
containing  copper,  342 

Calyces  of  the  kidney,  428 
Canal,  alimentary,  276.    See  Stomach, 
Intestine,  etc. 

external  auditory,  672 
function  of,  679 

spiral,  of  cochlea,  678 
Canaliculi  of  bone,  53 
Canalis  membranaceus,  678 
Canals,  Haversian,  54 

portal,  334 

semicircular,  675 

function  of,  685 
Cancellous  texture  of  bone,  51 
Capacity  of  chest,  vital,  235 

of  heart,  132 
Capillaries,  164 

circulation  in,  197 
rate  of,  206 

contraction  of,  200 

development,  786 

diameter  of,  165 

influence  of  on  circulation,  200 

lymphatic,  363 

network  of,  166 

number,  167 

passage  of  corpuscles  through  walb 

of'  T99  ,     ,  . 

resistance  to  flow  of  blood  in,  197 

still  layer  in,  ib. 

structure  of,  165 

of  lungs,  166 

of  stomach,  302 
Capric  acid,  856 
Caproic  acid,  ib. 
Capsule  of  Glisson,  332*' 
Capsules,  Malpighian,  429,  433 
Carbonic  acid  in  atmosphere,  238 

in  blood,  109 

effect  of,  252 

exhaled  from  skin,  425 

increase  of  in  breathed  air,  239 

in  lungs,  244 

in  relation  to  heat  of  body,  385 
Carbonates,  859 
Cardiac  orifice  of  stomach,  action  of,  310 

sphincter  of,  ib. 
relaxation  in  vomiting,  ib. 
Cardiac  revolution,  144 
Cardiograph,  148 
Carnivorous  animals,  food  of,  272 

sense  of  smell  in,  670 
Cartilage,  46 

articular,  ib. 

cellular,  49 

chondrin  obtained  from,  848 

classification,  46 

development,  50 

elastic,  49 

fibrous,  ib.     Sec  Fibro-cartilage. 

hyaline,  46 


INDEX. 


87I 


CaJLTTJ  ' 

Car*  United. 

matrix,  47 
ossification.  I  2 
perichondrium  "f,  64 
■tructure,  41  > 
temporary,  48 

*>  5° 
Tarietaes.  4'* 

Cartilage  01  external  ear,  used  in  hearing, 

679      ., 
Cartilages  of  larynx,  521 

1        a,  845,  846.     See  Milk. 
Cauda  equina.  ! 

Caudate  ganglion  corpuscles,  551 
Cause  of  fluidity  of  living  blood,  90 
Cells,  10 

abrasion.  17 

amoeboid,  35 

blood,  92.     See  Blood-corpuseles 

cartilage,  46 

chemical  transformation,  17 

ciliated,  29 

classification,  19 

contents  of,  11 

decay  and  death,  17 

definition  of,  10 

epithelium,  22.     See  Epithelium 

fission,  14,  15 

formative,  761 

functions,  16 

gemmation,  13 

gustatory,  664 

lacunar  of  bone,  53 

modes  of  connection,  19 

nutrition,  10 

action  of,  in  secretion,  289 

olfactory,  668 

pigment.  24 

reproduction,  13 

segmentation,  14 

structure  of,  10 

transformation,  17 

varieties,  18,  19 

vegetable,  8 

distinctions  from  animal  cells,  4 
Cellular  cartilage,  49 
Cement  of  teeth,  71 
Centres,  nervous,   191,    193,    &e. 
Xerve-eentres 

of  ossification,  66 
Centrifugal  nerve-fibres,  554 
Centripetal  nerve-fibres,  ib. 
Cerebellum,  595 

co-ordinating  function  of,  598 

cross-action  of,  599 

effects  of  injury  of  crura,  ib. 
of  removal  of,  597 

functions  of,  ib. 

in  relation  to  sensation,  ib. 
to  motion,  ib. 
to  muscular  sense,  ^98 
to  sexual  passion,  to. 

structure  of,  595 


Cklobu 

Cerebral  circulation,  208 

hemispheres,  600.    80*  Cerebrum 
Cerebral  nerr<  -. 

third,  620 

effects  of  irritation  and  injury  of, 

ib. 
relation  of  t"  iris,  ib. 

fourth,  621 
fifth. 
distribution  of, 
effect  of  division  of,  ib. 
influence  of  on  iris,  623 

on  muscles  of  mastication,  622 
on  organs  of  special  sense,,  O24. 
et  seq. 
relation  of,  to  nutrition,  625 
resemblance  to  spinal  nerves,  622 
sensory  function  of  greater   division 

of  fifth,  622 
sixth,  627 
communication    of,    with    sympa- 
thetic, 628 
seventh,     ib.      Sec  Auditory    Xerve 

and  Facial  Xerve 
eighth,  630,  et  seq.     Sec  Glossopha- 
ryngeal, Pneumogastrie,  and  Spinal 
Accessory  Nerves 
ninth,  635" 
Cerebration,  unconscious,  61 1 
Cerebrin,  850 

Cerebro-spinal  fluid,  relation  to  circula- 
tion, 209 
Cerebro-spinal    nervous    system,    564, 
>q. 
See  Brain,  Spinal  Cord,  &c. 
Cerebrum,  its  structure,  600,  604 
chemical  composition,  606 
convolutions  of,  601,  et  seq. 
crura  of,  590 
development,  799 
distinctive  character  in  man,  607 
effects  of  injury,  609 
electrical  stimulation,  613 
functions  of,  608 
grey  matter,  604 
in  relation  to  speech,  612 
localization  of  functions,  610 
structure,  604,  et  seq. 
unilateral  action  of,  610 
white  matter,  605 
Cerumen,  or  ear-wax,  417 
Chalk-stones,  444 
Characteristics    of   organic    compound, 

844 
Charcoal,  absorption  of,  381 
Chemical    composition    of   the   human 

body,  844—860 
Chest,  its  capacity,  235 
contraction  of  in  expiration,  321 
enlargement  of  in  inspiration,  228 
Chest-notes,  528 
Cheyne- Stokes'  breathing,  258 
Chlorine,  859 


8/2 


JXDEX. 


Chlokixe. 

Chlorine,  continued. 

in  human  body,  859 

in  mine,  449 
Cholesterin,  855 

in  bile,  341 
Chondrin,  848 
Chorda  dorsalis.  764 
Chorda  tynipaui,  286  et 
Chorda?  tendinea?,  135 

action  of,  139 
Chorion.  771 

villi  of,  772 
Choroid  coat  of  eye,  694 

blood-vessels,  699 
Choroidal  fissure,  804 
Chromatic  aberration.  711 
Chyle.  373 

absorption  of,  375 

analysis  of,  374 

coagulation  of,  lb. 

compared  with  lymph,  3  73 

corpuscles   of,  374.      See    Chyle-cor- 
puscles 

course  of,  361 

fibrin  of,  374 

forces  propelling,  375 

molecular  base  of,  373 

quantity  found,  373 

relation  of,  to  blood,  lb. 
Chyle-corpuscles,  374 
Chyme,  305 

absorption  of  digested  parts  of.  353 

changes  of  in  intestines,  353,  et  seq. 
Cilia,  29.  474 
Ciliary  epithelium,  29 

of  air  passages,  220 

function  of,  30 
Ciliary  motion,  30,  474 

nature  of,  475 
Ciliary-muscles,  702 

action  of  in  adaptation  to  distances. 

70S 

Ciliary  processes.  694 
Circulation  of  blood,  124 

action  of  heart.  137 

agents  concerned  10,211 

arteries.  171 

brain.  208 

capillaries,  197 

course  of,  124,  et  seq. 

discovery,  212 

erectile  structures,  210 

foetal,  796 

forces  acting  in,  127 

influence  of  respiration  ou,  253 

peculiarities    of,    in    different    parts, 
208 

portal.  334 

proofs,  212 

pulmonary.  244 

systemic,  126 

in  veins,  201 
velocity  of,  203 


Copper. 

Circumvallate  papilla?,  661 
Claviculi  of  Gagliardi,  57 
Cleft,  ocular,  804 
Clefts,  visceral,  782 
Clitoris.  742 

development  of,  818 
Cloaca,  816 

Clot  or  coagulum  of  blood,  81 
See  Coagulation, 
of  chyle,  374 
Coagulation  of  blood,  81 
absent  or  retarded,  88 
conditions  affecting,  ib. 
influence  of  respiration  on,  243 
theories  of,  87 
of  chyle.  374 
of  lymph,  ib. 
Coat,  bufly,  81 
Coats  of  arteries,  101 
Cochlea  of  the  ear,  671 

office  of,  682 
Cold-blooded  animals,  384 

extent  of  reflex  movements  in.  577 
retention  of  muscular  irritability  in, 

5°4 
Colloids,  379 
Colon,  323 
Colostrum,  408 
Colour-blindness,  726 
Colouring  matter, 

of  bile,  340 

of  blood.  103,  112 

of  urine.  446 
Colours,    optical   phenomena    of,    723, 

et  seq. 
Columna?  carnea?,  130 

action  of,  136 
Columnar  epithelium,  28 
Comple mental  air,  234 

colours.  72^ 
Compounds,  843 

inorganic,  857 

organic,  843 
Concha.  672 

use  of,  679 
Cones  of  retina,  697 
Coni  vasculosi.  731 
Conjunctiva,  691 
Connective  tissues.  ^ 

corpuscles  of,  ib. 

fibrous.  37 

gelatinous,  39 

retiform,  40 

varieties,  38 
Consonants,  532 

varieties  of,  ib. 
Contralto  voice,  326 
Convolutions,  cerebral,  601,  et  seq. 
Co-ordination  of   movements,   office  of 
cerebellum  in,  398 

office  of  sympathetic  ganglia  in.  642 
Copper,  an   accidental  element  in  the 
body,  860 


INDEX. 


873 


<    "ITER. 

Copper,  continued. 

in  bile,  y}2 
Cord,  spinal,  56  c.     s     Spinal  Cord 
umbilical, 

Is,  tendinous,  in  heart,  [35 
vocal,  520.     s"  Vocal  1  lori 
Corium,  413 
Cornea,  693 
action  of  on  rays  of  light,  700 
corpuscles,  (>g^ 
nerves,  ib. 
structure,  ib. 

after  injury  of  fifth  nerve,  626 
Corpora  Arantii,  136 
geniculata,  592 
quadrigemina,  ib. 

their  function,  ib. 
striata,  593 

their  function,  5^)4 
Corpus  callosum,  office  of,  615 
eayernosum  penis,  210 
dentatum 
of  cerebellum,  596 
of  olivary  body,  587 
luteuni,  747 

of  human  female,  747 
of  mammalian  animals,  ib. 
of    menstruation     and     pregnancy 
compared,  750 
spongiosum  urethra.-,  210 
Corpuscles    of   blood,  92.     See    Blood- 
corpuscles, 
of  chyle,  374 
of  connective  tissue,  ^ 
of  cornea,  693 
of  lymph,  374 
Pacinian,  547 
Correlation  of  life  with  other  forces,  818 
Cortical  substance  of  kidney,  428 

of  lymphatic  glands,  369 
Corti's  rods,  677 

office  of,  687 
Co>tal  types  of  respiration,  232 
Coughing,   influence  on   circulation  in 
veins,  256 
mechanism  of,  248 

isation  in  larynx  before,  559 
Cowper's  glands,  750 

office  uncertain,  756 
Cranial    nerves.      619.     See    Cerebral 

nerves. 
Cranium,  development  of,  799 
Crassamentum,  81 
Crescents  of  Gianuzzi,  281.     See  Semi- 

lunes  of  Heidenhain. 
Crico-arytenuid  muscles,  52 1 
Cricoid  cartilages,  ib. 
Crossed  pyramidal  tract,  572 
Crura  cerebelli, 

effect  of  dividing,  598,  et  seq. 
of  irritating,  ib. 
cerebri,  590 
their  office,  591 


DBS!   I  Mil"-    M  1  MI1UANE. 

Crusts  petrosa,  71 

Cryptogamic     plant-,    movement 

s]  11  lies  Of,  4 

Crystal  growth  of,  2 
Crj  stallin, 
Crystalline  lens,  700 

in  relation  to  vision   at  different 
distances,  704 
Crystalloids,  37^ 

dlood,  112 
Cubic  feet  of  air  for  rooms,  253 
Cupped  appearance  of  blood-clot,  82 
(  urdling  ferments,  307,  854 
Currents  of  action,  502 

ascending,  515 

continuous,  490 

descending,  515 

induced,  492 

muscle,  487 

natural,  488 

negative  variation,  502 

nerve,  513 

polarising,  515 

rest,  488,  513 
Curves,  Traube-Hering's,  258 
Cuticle,  410.  See  Epidermis,  Epithelium. 

of  hair,  419 
Cutis  anserina,  476 

vera,  413 
Cy;mate  of  ammonium,  442 
Cylindrical  or  columnar  epithelium,  28 
Cystic  duct,  332 
Cystin  in  urine,  449 


1). 


Daltonism,  726 
Daniell's  battery,  490 
Decidua, 

menstrualis,  745 

reflexa,  775 

serotina,  ib. 

vera,  774 
Decline,  3 

Decomposition,  tendency  of  animal  com- 
pounds to,  844 
Decomposition-products,  848 
Decussation   of  fibres   in  medulla  ob- 
longata, 585 
in  spinal  cord,  576 

of  optic  nerves,  732 
Defa-cation,  mechanism  of,  357 

influence  of  spinal  cord  on,  581 
Deglutition,  291.     Sec  Swallowing. 
Dentine,  67 
Depressor  nerve,  192 
Derived  albumins,  846 
Derma,  413 

Descendens  noni  nerve,  635 
Descemet's  membrane,  693 


8/4 


IXDEX. 


Development. 

Development,  3,  757 
of  organs,  778 
alimentary  canal,  806 
arteries,  791 
blood,  119,  et  seq. 
blood-vessels,  786 
bone,  57 
brain,  799 
capillaries,  786 
cranium,  799 
ear,  805 
embryo,  761 
extremities,  784 
eye,  802 

face  and  visceral  arches,  7S2 
heart,  785 
liver,  809 
lungs,  ib. 

medulla  oblongata,  801 
muscle,  483 
nerves,  798 
nervous  system,  ib. 
nose.  806 

organs  of  sense,  802 
pancreas,  808 
pituitary  body,  781 
respiratory  apparatus,  810 
salivary  glands,  808 
spinal  cord,  798 
teeth.  71 

vascular  system,  785 
veins,  793" 

vertebral  column  and  cranium,  778 
viscera]  arches  and  clefts,  782 
of  Wolffian  bodies,  urinary  apparatus 
and  sexual  organs,  810 
Dextrin,  285 
Diabetes,  351 
Diamides,  848 

Diapedesis  of  blood-corpuscles,  198 
Diaphragm, 

action  of,  on  abdominal  viscera,  218 
in  inspiration,  228 
in  various  respiratory  acts,  245 
in  vomiting,  310 
Diaphysis,  66 
Diastole  of  heart,  137 
Dicrotous  pulse,  182 
Diet- 
daily,  272 

influence  on  blood,  107 
mixed,  necessity  of,  263,  et  seq. 
Diffusion  of  gases  in  respiration,  244 
Digestion,  276 

in  the  intestines,  352,  355 
in  the  stomach,  305 
influence  of  nervous  system  on,  360 
of  stomach  after  death*,  313 
See  Gastric  fluid,  Food,  Stomach. 
Diplopia,  729 
Direct  cerebellar  tract,  572 

pyramidal  tract,  571 
Direction  of  sounds,  perception  of,  688 


Emmetropic  Eye. 

Discus  proligerus,  739 
Disdiaclasts,  479 

Distance,  adaptation  of  eye  to,  703 

of  sounds,  now  judged  of,  689 
Distinctness  of  vision,  how  secured,  699, 

et  seq. 
Dormant  vitality,  821 
Dorsal  laminae,  762,  782 
Double  healing,  690 

vision,  730 
Dreams,  618 

Drowning,  cause  of  death  in,  261 
Duct,  cystic,  332 

hepatic,  336 

thoracic,  361    , 

vitelline,  767 
Du-tless  glands,  461 
Ducts  of  Cuvier,  795 
Ductus  arteriosus,  792 

venosus,  795,  796 

closure  of,  798 
Duodenum,  315 

Duration  of  impressions  on  retina,  714 
Duvemey's  glands.  793 
Dysphagia,  absorption    from    nutritive 

baths  in,  427 
Dyspnoea,  259 


1:. 


Ear,  671 
bones  or  ossicles  of,  673 

function  of,  682 
development  of,  805 
external,  672 
function  of,  679 
internal,  674 

function  of,  685 
middle,  673 
function  of,  680 
Ectopia  vesicae,  459 
Efferent  nerve-fibres,  554 
lymphatics,  372 
vessels  of  kidney,  433 
Egg-albumin,  845" 
Eighth  cranial  nerve,  630 
Elastic  cartilage,  49 
fibres,  36 
tissue,  39 
Elastin,  848 
Electricity, 
in  muscle,  485 
nerve,  513 
retina,  717 
Electrodes,  486 
Electrotonus,  515 

Elementarv  substances  in  the  human 
body,  843 
accidental,  860 
Embryo,  761,  et  seq.     See  Development 
and  Foetus,  formation  of  blood  in,  1 19 
Emmetropic  eye,  708 


INDEX. 


875 


Emotions. 

Emotions,  connection  of  with  cerebral 

hemispheres,  608 
Enamel  of  teeth,  70 
Enamel  organ,  71 
End-bulbs,  416 
End-plates,  motorial,  549 
Endocardium,  134 
Endol]  mph,  074 

fanction  of,  605 
Endomysiuni,  478 
Endoneurium,  541 
Endosmometer,  378 
Endothelium,  24 

distinctive  characters,  ib. 

germinating,  27 

Energy,  536  .        . 

relations  of  vital  to  physical,  chap.  xx. 

daily  amount  expended  in  body,  536 

Epencephalon,  801 

Epiblast,  760 
Epidermis,  411 
development,  etc.,  of,  412 
functions  of,  422 
hinders  absorption,  413 

pigment  of,  412 

relation  to  sensibility,  423 

structure  of,  41 1 

thickening  of,  412 
Epididymis,  751 
Epiglottis,  520 

action  in  swallowing,  294 

influence  of  on  voice,  524 
Epineurium,  541 
Epiphysis,  66 
Epithelium,  22 

air-cells,  225 

arteries,  161 

bronchi,  220 

bronchial  tubes,  ib. 

ciliated,  29 

cogged,  24 

columnar,  28 

cylindrical,  ib. 

development,  32 

glandular,  27 

goblet-shaped,  29 

growth,  32 

mucous  membranes,  397 

olfactory  region,  668 

secreting  glands,  399 

serous  membranes,  394 

spheroidal,  27 

squamous  or  tesselated,  23 

transitional,  30 
Erect  position  of  objects,  perception  ot, 

7l8  ,    •      • 

Erectile  structures,  circulation  in,  210 

Erection,  ib. 

cause  of,  ib. 

influence  of  muscular  tissue  in,  to. 

a  reflex  act,  581 
Erythro-granulose,  583 
Erythro-dextrin,  853 


Facial  Nbkvb. 

Eunuchs,  voice  "i',  527 
Eustachian  tube,  673 

development. 

fanction  of,  <>84 
Eustachian  valve,  [29 
Excito-motor    and    senaon-motor 

560 
Excreta  in  relation  to  muscular  action, 

512,  Ct  srq. 

Excretin,  356 

Excretion,  427 
Excretoleic  acid,  356 
Exercise, 

effects  of,  on  production  of  carbonic 
acid,  240 
on  temperature  of  body,  383 
on  venous  circulation,  202 
Expenditure  of  body,  534 

amount,  534 

compared  with  income,  535 

evidences,  534 

objects,  53O 

sources,  ib. 
Expiration,  231 

influence  of,  on  circulation,  255 

mechanism  of,  231 

muscles  concerned  in,  232 

relative  duration  of,  233 
Expired  air,  properties  of,  239,  et  seq. 
Extractive  matters, 

in  blood,  106 

in  urine,  447 
Extremities,  development  oi,  784 

Eye,  691 

adaptation  of  vision  at  different  dis- 
tances, 699,  ct  seq. 
blood-vessels,  698 
capillary  vessels  of,  694 
development  of,  802 
effect  on,  of  injury  of  facial  nerve, 
628 
of  fifth  nerve,  625,  627 

effect  of  pressure  on,  730 

nerves,    supplying   muscles  of,    620, 
621,  627 

optical  apparatus  of,  699 

refracting  media  of,  700 

resemblance  to  camera,  712 

structure  of,  692 
Eyelids,  691 

development  of,  005  .  . 

Eyes,  simultaneous  action  of  in  vision, 
729 


F. 


Face,  development  of,  782 

effect  of  injury  of  seventh  nerve  on, 
628 
Facial  nerve,  628 

effects  of  paralysis  of,  ib. 


8y6 


IXDEX. 


Facial  Xerve. 

Facial  nerve,  continued. 

relation  of,  to  expression,  628 
Faeces,  composition  of,  356 

quantity  of,  ib. 
Fallopian  tubes,  741 

opening  into  abdomen,  ib. 
Falsetto  notes,  528 
Fasciculus, 

cuneatus,  572 

olivary,  ib. 

teres,  lb. 
Fasting, 

influence  on  secretion  of  bile,  342 
Fat.     See  Adipose  tissue. 

action  of  bile  on,  346 

of  pancreatic  secretion  on,  331 
of  small  intestine  on,  353 

absorbed  hy  lacteals,  375 

formation  of,  538 

in  blood,  106 

in  relation  to  heat  of  body,  390 

of  bile,  341 

of  chyle,  374 

situations  where  found,  42 

uses  of,  45 
Fechner's  law,  715 
Female  generative  organs,  736 
Fenestra  ovalis,  674 

rotunda,  675 
Ferments,  85,  285,  305,  330,  331 
Fibres,  20 

of  iM  filler,  698 
Fibrils  or  filaments,  20 
Fibrin,  847,  in  blood,  81    * 
use  of,  123 

in  chyle,  374 

formation  of,  81 

in  lymph,  374 

sources  and  properties  of,  847 

vegetable,  267 
Fibrinogen,  84,  et  seq. 
Fibrinoplastiu,  ib. 
Fibro-cartilage,  49 

classification,  ib. 

development,  ib. 

uses,  ib. 

white,  ib. 

yellow,  ib. 
Fibrous  tissue,  37 

white,  37 

yellow,  38 

development,  40 
Field  of  vision,  actual  and  ideal  size  of, 

719 
Fifth     nerve,      622.         See     Cerebral 

Nerves. 
Fillet,  584 
Filtration,  401 
Filum  terminate,  565 
Fimbriae  of  Fallopian  tube,  741 
Fingers,  development  of,  784 
Fish, 
temperature  of,  384 


33r, 


Fundus  of  Bladder. 

Fissures, 

of  brain,  601,  et  seq. 

of  spinal  cord,  566 
Fistula,  gastric,  experiments  in  cases  of, 

303,304 
Flesh,  of  animals,  265 
Fluids,  passage  of,  through  membranes, 
„      378 

Fluoride  of  calcium,  859 
Focal  distance,  703 
Foetus, 

blood  of,  119 

circulation  in,  796 

communication  with  mother,  776 

faeces  of,  344 

membranes,  767 

office  of  bile  in,  ib. 

pulse  in,  151 
Folds,  head  and  tail,  765 
Follicles,  Graafian,  738.      See  Graafian 

Vesicles. 
Food,  262 — 276 

all  mminous,  changes  of,  305 

amyloid,     changes      of,    28 

M  , 

ol  animals,  272 

of  carnivorous  animals,  ib. 

classification  of,  264 

composition      of     many,      845,      et 

seq. 
digestibility  of  articles  of,  307 

_  value  dependent  on,  275 
digestion    of,   in    intestines,   353,   et 
seq. 
in  stomach,  307,  et  seq. 
improper,  272 
of  man,  263 

mixed,  the  best  for  man,  263 
mixture  of,  necessary,  264 
relation  of,  to  carbonic  acid  produced, 
240 
to  heat  of  body,  385 
to  muscular  action,  512 
relation  of,  to  urea,  456 
to  urine,  440 
phosphates  in,  448 
table  of,  275 
too  little,  269 
too  much,  273 
vegetable,  contains  nitrogenous  prin- 
ciples, 267 
Foot-pound,  154 
Foot-ton,  ib. 
Foramen  ovale,  130 
Forced  movements,  599 
Form  of  bodies,  how  estimated,  721 
Formation  of  fat,  538 
Formic  acid,  856 
Fornix,  office  of,  616 
Fourth  cranial  nerve,  621 

ventricle,  =584 
Fovea  centralis,  713 
Fundus  of  bladder,  436 


[NDEX. 


877 


Fundus  of  uterus.  - 
Fungiform  papillto  of  t 


(.. 


ictophoroua  ducts,  406 
Gall-blad 
functions, 

»f  bile  into  ami  from,  342 
structure  . 

N  itres. 

spinal  nen 
of  the  Bympathetn  . 
action  of,  640,  it  seq. 

co-ordinators    of     involuntary 
movement-,  '42 
structure  of,  637 
in  heart,  155 

in  sub>tance  of  organs,  642 
Ganglion,  Gaasexian,  I  22 
co:  ^50 

Nerve-corpuscles. 
-.  S43 
in  bile,  341 
in  blood,  1 09 
extraction  of,  lb. 
extraction  from  blood,  lb. 
in  stomach  and  intestines,  367 
in  urine,  450 
Gastric  glands,  299 
Gastric  juice,  303 
acid  in,  304 

action  oi,  on  nitrogenous  food,  305 
on  non-nitrogenous  food,  307 
on    saccharine  and  amyloid  prin- 
cdpli  s, 
artificial,  305 

preparation  of,  ib. 
characters  of,  303 
composition  of,  304 
digestive  power  of,  305 
experiments  with. 
pepsin  of,  lb. 
quantity  of,  304 
ration  of,  303 
how  excited,  lb. 

influence  of  nervous  system  on,  312 
Gelatin,  847 

ai  *  -    -trie  juice  on,  307 

action  of  pancreatic  juice  on,  331 
Gelatinous  substances,  S47 
Generation  and  development,  730 
Generative  organs  of  the  female,  ib. 

of  the  male,  750 
Genito-urinary  tract  of  mucous  mem- 
brane, 397 
Ger lath's  network,  568 
Germinal  area,  761 
epithelium,  737 
matter,  6.     See  Protoplasm. 


■:•    T. 

minal  membrane,  760 

•  74° 
•  1>  vclojunent,  ib. 

. 

'.  ipmenl  of,  \b. 
ippearance  of,  ; 

Gill,  214 

Gland,  pineal.  472 
pituitarj . 

prostate,  750,  756 

Gland-cells,  .._  IQ2 

changes  in  during  secretion,  289,  301, 

relation  to  epithelium.  398 
Gland-ducts,  arrangement  of,  402 

contractions  of,  403 
Glands,  aggregate,  399 
Brunners,  318 

ceruminous,  417 

Cowper's,  750 

ductless,  4'ji.  ilar. 

Duvernev's,  743 

of  large  intestine, 

of  Lieberkiihn.  317 

lymphatic,     368.       Sec      Lymphatic 
Glands. 

mammary,  405 

of  Peyer,  318 

salivary,  279 

sebaceous,  417 

secreting,  39^.      5     v    reting  Gl 

of  small  intestines,  317 

of  stomach,  299 

sudoriferous,  416 

tubular,  399 

vascular,  461.     See  Vascular  Glands. 

vulvo-vaginal,  743 
Glandula  Xabothi,  742 
1  rlisson's  capsule,  ^2 
Globulin,  106,  846 

distinctions  from  albumin,  846 
Globus  major  and  minor,  751 

development,  812 
Glosso-pharyngeal  nerve,  285,  630 

communications  of,  ib. 

motor  filaments  in,  ib. 

a  nerve  of  common  sensation  and  of 
•  630 
Glottis,  action  of  laryngeal  muscles  on, 

,      5" 
closed  m  vomiting,  311 

effect   of  division    of    pneumogastric 
nerves  on,  '»34 

forms  assumed  by,  523 

narrowing  of,  proportioned  to  height 
of  note.  524 

respiratory  movements  of,  234 
Glucose,  E 

in  liver,  350 

test  for,  284 
Gluten  in  vegetables,  267 
Glycerin  extract,  305,  329 


8j8 


IXDEX. 


Glycix. 

Glyoin,  849 
Grlycochohc  acid.  ib. 
Glycogen,  350,  855 
characters,  350 

destination,  349 

preparation,  350 

quantity  fonned,  349 

variation  with,  diet,  ib. 
Glycosuria,  351 

artificial  production  of,  ib. 
Goll's  column,  572 
Graafian  vesicles,  738 

formation  and  development   of,  738, 
etseq. 

relation  of  ovum  to,  739 

rupture  of,  changes  following,  743 
Granular  layers  of  retina,  694 
Grape-sugar,  856.     See  Glucose. 
Grey  matter  of  cerebellum,  595 

of  cerebrum,  604 

of  crura  cerebri,  590 

of  medulla  oblongata,  587 

of  pons  Varolii,  590 

of  spinal  cord,  568 
Groove,  primitive,  762 
Growth,  2, 

coincident  with  development,  3 

of  bone,  66 

not  peculiar  to  living  beings,  2 
Guanin,  851 

Gubernaculum  testis,  815 
Gullet,  292 
Gustatory  nerves,  659 

cells,  664 


H. 


Habitual  movements,  562 
Hsematin.  no 

hydroehlorate  of,  117 
Hamiadynamonieter,  186 
Ha?matochometer,  206 
Haematoidin,  116 
Haemin,  117 
Hsemocytometer,  101 
Haemoglobin,  112,  et  seq. 

action  of  gases  on,  115 

distribution,  118 

estimation  of,  118 

spectrum,  114 
Hair-follicles,  420 

their  secretion,  423 
Hairs,  418 

chemical  composition  of,  848 

structure  of,  418 
Hamulus,  676 
Hare-lip,  783 

Hassall,  concentric  corpuscles"  of,  467 
Haversian  canals,  54 
Hearing,  anatomy  of  organ  of,  671 


Heat. 

Hearing,  continued. 
double,  690 

impaired  by  lesion  of  facial  nerve,  629 
influence  of  external  ear  on,  672 

of  labyrinth,  68s 

of  middle  ear,  680 
physiology  of, 678 
See  Sound,  Vibrations,  etc. 
Heart,  127-159 
action  of,  137 

accelerated,  158 

effects  of,  153 

force  of,  151 

frequency  of,  ib. 

inhibited,  157 

after  removal,  ib. 

rhythmic,  153 

work  of,  154 
auricles  of  128,  137 

See  Auricles, 
capacity,  132 
chambers,  128 
chorda?  tendinea?  of,  135 
column  a?  carnae  of,  130,  136 
course  of  blood  in,  134 
development,  785 
endocardium,  128 
force,  181 
frog's,  154 
ganglia  of,  155 
impulse  of,  147 

tracing  by  cardiograph,  148,  et  $eq. 
influence  of  pneumogastric  nerve,  156 

of  sympathetic  nerve,  158 
investing  sac,  127 
muscular  fibres  of,  132 
musculi  papillares,  135,  140 
nervous  connections  with  other  organs, 

157      r 
rhythm,  156 
nervous  system,  influence  on,  134 
revolution  of,  144 
situation,  127 
sounds  of,  145 
causes,  146 
structure  of,  132 
tendinous  cords  of.  135 
tubercle  of  Lower  in,  129 
valves,  135 

arterial  or  semilunar,  136 

function  of,  141 
auriculo-  ventricular,  135 
function  of,  139 
ventricles,  their  action,  138 

capacity,  132 
weight  of,  ib. 
work  of,  154 
Heat,  animal,  382.     See  Temperature, 
influence  of  nervous  system,  390 
of  various  circumstances  on,  382, 
et  seq. 
losses  by  radiation,  etc.,  387 
in  relation  to  bile,  345 


[NDEX. 


879 


Heat. 

Heat,  eoniin 
sources   and    modei    of    production, 

developed  in  contraction  of  muscles, 

382,386, 
perception  of, 

391 
II    it-producing  tissues,  386 

Heat  or  rut,  743 

analogous  to  menstruation,  ib. 
Height,  relation  to  respiratory  capacity, 

*35 
Helicotrema,  676 

Helix  of  car,  1  72 
Hemipcptoiu',  847 

Hemispheres,  Cerebral,  600.     See  Cere- 
brum 
Hepatic  cells,  333 

duets,  336 

nim,  335 

characters  of  blood  in,  IOo 

vessels,  arrangement  of,  334,  et  seq. 
Herbivorous  animals, 

perception  of  odours  by,  670 
Hering's  theory,  724 
Hermaphroditism,  apparent,  818 
Hiccough,  mechanism  of,  247 
Hip-joint,  pain  in  its  diseases,  559 
Hippuric  acid,  446.  458,  849 
Horse's  blood,  peculiar  coagulation  of, 

82 
Howship's  lacunae,  53 
Hunger,  sensation  of,  270 
Hyaline  cartilage,  46 
Hybernation,  state  of  thymus  in,  468 
Hydrogen,  843 

Hydrolytic  ferments,  284,  852 
Hymen,  742 
Hyperesthesia, 

result  of  injury  to  spinal  cord,  576 
Hypermetropia,  709 
Hypoblast,  760 
Hypoglossal  nerve,  633 
Hypospadias,  818 
Hypoxanthin,  851 


1. 


Ideas,  connection  of,  with  cerebrum,  609 

Ileum,  31C 

Ileo-ca?cai  valve,  326 

Illusions  of  touch,  655 

Image,  formation  of,  on  retina,  700 

distinctness  of,  708 

inversion  of,  717 
Impulse  of  heart,  147 
Income  of  body,  535 

compared  with  expenditure,  ib. 
Incus, 

function  of,  673 
Indican,  446 


Irradiation. 
Indigo,  852 

Illddl,    33O 

Induction 

•  nil,  492 

current,  ib. 
Infundibulum.  224 
Inhibitory  influence  of  pnc. 

liervi  ,    ' 

Inhibitory  action  of  brain,  53 
nerves,  554 

action  of,  on  heart,  156 
on  blood-vessels,  193 
on  blood- vesselsof  salivary  glands, 

286,  ei  se/. 
on  gastric  blood-vessels,  312,  et 

S"/. 

on  intestinal  movements,  359 
on  respiratory  movements,  249 
Inhibitory  heat-centre,  391 
Inorganic   matter,  distinction  from  or- 
ganised, 844,  et  so/. 

principles,  857 
Inosite,  856 
In  salivation,  279 
Inspiration,  227 

elastic  resistance  overcome  by,  23O 

extraordinary,  231 

force  employed  in,  237 
durum  dyspnoea,  259 

influence  of,  on  circulation,  253 

mechanism  of,  228 
Intercellular  substance,  20 
Intercostal  muscles,  action    in  inspira- 
tion, 229,  et  seq. 

in  expiration,  231 
Interlobular  veins,  336 
Intestinal  juice,  351 
Intestines,  digestion  in,  352,  355 

development,  807 

fatty  d'iseh  irges  from,  331 

gases,  367 

large,  digestion  in,  355 
structure,  325 

length  in  different  animals,  352 

movements,  359 

small,  changes  of  food  in,  352 
structure  of,  315 
Intonation,  527,  et 
Intralobular  veins,  336 
Inversive  ferments,  352 
Involuntary  muscl 

actions  of,  3 1 1 

struetu 
Iris,  701 

action  of,  701,  et  seq. 

in  adaptation  to  distances,  705 

blood-vessels,  701 

development  of,  805 

influence  of  fifth  nerve  on,  702 
of  third  nerve,  ib. 

relation  of,  to  optic  nerve,  ib. 
Iron,  859 
Irradiation,  712 


'311 

of,  47c 


88o 


INDEX. 


Ivory. 
Ivory  of  teeth,  70 


Jacob's  membrane,  697 
Jacobson's  nerve,  630 
Jaw,  interartieular  cartilage,  27! 
Jejunum,  315 
Juice,  gastric,  303 
pancreatic,  330 
Jumping,  511 


K. 


Karyokinesis,  15 

Katacrotic  wave,  182 

Katelectrotonus,  516 

Keratin,  307 

Key,  491 

Kidneys,  their  structure,  428 

blood-vessels  of,  how  distributed,  433 

capillaries  of,  424 

development  of,  812 

function  of,  437.     #00  Urine. 

Malpighian  corpuscles  of,  429 

nerves,  435 

tubules  of,  429 
Knee,  pain  of,  in  diseased  hip,  559 
Krause's  membrane,  480 
Kreatinin,  447 
Kymograph,  186 

tracings,  186,  et  scq. 

spring-,  187 


L. 


Labia  externa  and  interna,  742 
Labyrinth  of  the  ear,  674  et  seq. 

membranous,  678 

osseous,  674 

function  of,  685 
Lachrymal  apparatus,  691 

gland,  ib. 
Lactation,  406 
Lacteals,  302 

absorption  by,  375 

contain  lymph  in  fasting,  373 

origin  of,  363 

structure  of,  364 

in  villi,  324 
Lactic  acid,  857 

in  gastric  fluid,  304 
Lactiferous  ducts,  406 
Lactose,  266,  409 
Lacuna?  of  bone,  53 
Lamellae  of  bone,  55 


Liver. 

Lamina  spiralis,  676 

use  of,  686 
Lamina?  dorsales,  762 

viscerales  or  ventrales,  767 
Language,  how  produced,  530 
Large  intestine,  325.     See  Intestine. 
Larynx,  construction  of,  520 

muscles  of,  521 

nerves  of,  522 

variations  in  according  to  sex  and  age, 

527 

ventricles  of,  530 

vocal  cords  of,  520 
Latent  period,  497 
Laughing,  248 

Laxator  tympani  muscle,  685 
Lead  an  accidental  element,  860 
Leaping,  54 
Lecithin,  341 

Legumen  identical  with  casein,  267 
Lens,  crystalline,  700 
Lenticular  ganglion,  relation  of  third 

nerve  to,  625 
Leucic  acid,  857 
Leucin,  330 
Leucocytes, 

of  blood,  98 

amoeboid  movements,  99 

chyle,  374 

lymph,  372 

origin  of,  122 
Leucocythsemia,  state  of  vascular  glands 

in,  464 
Levers,  different  kinds  of,  507 
Lieberkiihn's  glauds, 

in  large  intestines,  326 

in  small  intestines,  317 
Life,  837 

relation  to  other  forces,  818 

simplest  manifestations  of,  8 
Ligamentum  nucha?,  39 
Lightning,  condition  of  blood  after  death 

by,  89 

Lime,  salts  of,  in  human  body,  859 

Lingual  branch  of  fifth  nerve,  285 

Lips,  influence  of  fifth  nerve  on  move- 
ments of,  624 

Liquor  amnii,  770 

Liquor  sanguinis,  or  plasma,  78 
lymph  derived  from,  376 
still  layer  in  capillaries,  197 

Lithium,  absorption  of  salts  of, 

Liver,  332 

action    of,    on   albuminous    matters, 

348 
on  saccharine  matters,  349 
blood-elaborating  organ,  347 
blood-making  organ,  120 
blood-vessels  of,  336 
capillaries  of,  ib. 
cells  of,  333 
circulation  in,  334 
development  of,  809. 


IX  I)  EX. 


83i 


I.I\  ER. 

Liv.T.  '•  mtinued. 

duets  of,  3  v 

fanotiona  of,  338 
in  foetus,  J 1 1 

gljoogenio  function  of,  148 
of,  338.     s'  •  Bile. 

structure  of,  1  ]  J 

sugar  formed  by,  350  ft  •#?. 
Locus  niger,  51  - 1 
Loss  of  water.  858 
Ludwig'a  air  pump,  no 
Lungs,  221 

blood-supply. 

capillaries  of,  166 

cells  of,  223 

ehangea  of  air  in,  238 

changes  of  blood  in,  244 

circulation  in, 

contraction  of,  237 

coverings  of,  222 

development  of,  810 

elasticity  of,  23 1 

lobes  of,  223 

lobules  of,  223 

lymphatics,  226 

muscular  tissue  of,  237 

nerves,  227 

nutrition  of,  226 

position  of,  215 

structure  of,  222 
Luxus  consumption,  274 
Lymph,  373    . 

compared  with  chyle,  373 
with  blood,  374 

current  of,  368 

quantity  formed,  375 

source  of,  376 
Lymph-corpuscle?,  373 

in  blood,  122 

development  of  into   red  blood-cor- 
puscles, ib. 

origin  of,  ib. 
Lymph-hearts,  structure  and  action  of, 

37  i  .  . 

relation  of  to  spinal  cord,  377 

Lymphatic  glands,  368 
Lymphatic  vessels,  361 

"absorption  by,  37O 

communication  with   serous  cavities, 

365 
communication  with  blood-vessel 

contraction  of,  368 

course  of  fluid  in,  368 

distribution  of,  361 

origin  of,  363 

propulsion  of  lymph  by,  368 

structure  of,  368  t  i 

valves  of,  368 

Lymphoid  or  retiform  tissue,  4c. 

Adenoid  Tissue. 


MkMHRANA    Ll.MITAN-     KtEIINA. 


M 


Macula  germinatira, 

M  iirnesium.  859 

Male  sexual  function*,  75  1 

Mullens,  (173 

function  of,  <>s2 
M alpighian  bodies  or  corpuscles  of  kid- 
ney, 429 

capsules,  ib. 

corpuscles  of  spleen,  4O4 
Maltose,  285,  853 
Mammalia, 

blood-corpuscles  of,  96 

brain  of,  606 
Mammary  glands,  405 

evolution,  407 

involution,  407 

lactation,  406 
Mandibular  arch,  783 
Manganese,  860 
Manometer,  186 

experiments     on    respiratory     power 
with,  238 
Marrow  of  bone,  52 
Mastication,  278 

fifth  nerve  supplies  muscles  of,  278 

muscles  of,  278 
Mastoid  cells,  673 
Matrix  of  cartilage,  46 

of  nails,  421 
Mature  corpuscles, 

origin  of,  120 
Meatus  of  ear,  672 

urinarius,  opening  of  in  female,  742 
Meckel's  cartilage,  7S3 
Meconium,  344 
Medulla  of  bone,  52 

of  hair,  420 
Medulla  oblongata,  583  et  8eq. 

columns  of,  583 

conduction  of  impressions,  587 

decussation  of  fibres,  584 

development,  801 

effects  of  inj  ury  and  disease  of,  588 

fibres  of,  how  distributed,  585 

functions  of,  587  et  teq. 

important  to  life,  588 

nerve-centres  in,  58S 

pyramids  of,  anterior,  584 
"  posterior.  -" !  5 

structure  of.   584 
Medullary  portion  of  kidney,  420 

substance  of  lymphatic  -lands.  369 

substance  of  nerve  fibre,  543 
Melanin,  852 
Membrane  decddua,  745 

granulosa,  739 

development  of  into  corpus  luteum , 

747 
limitans  externa,  O97 

interna,  695 

3    L 


882 


INDEX. 


Memrrana  Propria. 

Membrana  propria   or  basement  mem- 
brane, 397.      See  Basement  Mem- 
brane. 
papillaris,  805 

capsulo-pupiHari*,  ib. 
tympani,  673 
office  of.  680 
Membrane,  blastodermic,  760 
Jacob's,  697 

of  the  brain  and  spinal  cord,  5^4 
ossification  in,  57 

primary  or  basement,  394.     Sec  Base- 
ment membrane, 
vitelline,  739 
Membranes,  mucous,  396.     See  Mucous 

membranes. 
Membranes,  passage  of  fluids  through, 
366 
secreting,  398 
Membranes,   serous,   394.      See  Serous 

membranes. 
Membranous  labyrinth,  678 
Memory,    relation     to    cerebral     hemi- 
spheres, 608  et  seq. 
Menstrual     discharge,    composition    of, 

Menstruation,  744 

coincident  with  discharge  of  ova,  744 

corpus  luteum  of,  747 

time  of  appearance  and  cessation,  747 
Mental  derangement,  609 

exertion,  effect  on  heat  of  body,  391 
on  phosphates  in  urine,  448 

faculties,  development  of  in  proportion 
to  brain,  609 
theory  of  special  localisation  of,  610 
et  seq. 

field  of  vision,  719 
Mercurial  air-pump,  no 
Mercurial  manometer,  185 
Mercury,  absorption  of,  426 
Mesencephalon,  801 
Mesenteric  veins,  blood  of,  108 
Mesoblast,  760 
Mesocephalon,  590 
Metalbumin.  845 
Metallic    substances,    absorption   of  by 

skin,  426 
Metencephalon,  801 
Metha?nioglobin,  115 
Mezzo-soprano  voice,  426 
Micturition,  460 
Milk,  as  food,  307 

chemical  composition,  409 

properties  of,  409 

secretion  of,  406 
Milk-curdling  ferments,  331,  410 
Milk-globules,  409 
Miik-teeth,  77  et  seq. 
Millon's  re-agent,  845 
Mind,  cerebral  hemisphere  the   organs 
of,  608 

influence  on  action  of  heart,  154 


Mucus. 

Mind,  continued. 
influence  on  animal  heat,  391 

on  digestion,  360 

on  hearing,  689 

on  movements  of  intestines,  360 

on  secretion,  404 

on  secretion  of  saliva,  286 

in  vision,  719  et  seq. 
power  of  concentration  on  the  senses, 

"23  .  . 

of  exciting  sensations,  G49 

Mitral  valve,  133 
Modiolus,  675 
Molecules,  or  granules,  8 

in  blood,  94 

in  milk,  409 

movement  of  in  cells,  8 
Molars,  75 
Molecular  base  of  chyle,  373 

motion,  8 
Monamides,  848 
Motion,     causes    and    phenomena    of, 

474 
amoeboid,  8,  99,  475 

ciliary,  7,  474 

molecular,  8 

muscular,  488  et  seq. 

of  objects,  now  judged,  722 

power  of,  not   essentially   distinctive 

of  animals,  4 
sensation  of,  650 
Motor  impulses,  transmission  of  in  cord, 

576 

nerve-fibres,  554 

laws  of  action  of,  357 
Motor  linguae  nerve,  635 

oculi,  or  third  nerve,  620 
Motorial  end-plates,  549 
Mouth,  changes  of  food  in,  2~6et  seq. 
Movements, 

of  eyes,  728 

of  intestines,  359 

of  voluntary  muscles,  507 

produced    by   irritation    of    auditory 
nerve,  690 
Mucigen,  290 
Mucin,  290 
Mucous  membrane,  396 

basement  membrane  of,  397 

capillaries  of,  167 

epithelium-cells  of,  398.     See  Epithe- 
lium. 

digestive  tract,  39S 

gastro-pulmonary  tract,  397 

genito-urinary  tract,  397 

gland-cells  of,  397 

of  intestines,  315,  325 

of  stomach,  298 

of  tongue,  661 

of  uterus,  changes  of  in  pregnancy,  773 

respiratory  tract,  397 
Muco-salivary  glands,  282 
Mucus,  398 


INDEX. 


883 


Mi  1 

Mmus,  continued. 
in  bue,  341 

in  urine,  44*) 

of  mouth,  mixed  with  saliva,  283 
Mullcr's  fibres,  698 
Bfurexide,  445,  851 
Musi  Lee, 

activity,  488 

changes  in,  by  exercise,  500 

chemical  constitution,  485,  502 

clot,  485 

contractility,  488 

con  tract  ion,  mode  of,  4'  4 

corpuscles,  481 

curves,  41)7  / 1  teq.  ;  502 

development,  483 

disc  of  Hensen,  480 

effect  of  pressure  of,  on  veins,  202 

elasticity,  484 

electric  currents  irj,  485,  502 

fatigue,  499 
curves,  to. 

growth,  4S4 

heart,  482 

heat    developed     in   contraction     of, 
500 

involuntary,  476 
actions  of,  503,  511 

Krause's  membrane,  480 

muscle-rods,  482 

natural  currents,  485 

nerves  of,  483 

non-striated,  476 

nutrition  of,  483 

physiology  of,  484 

plain,  476 

plasma,  483 

reaction,  485 

response  to  stimuli,  503 

rest  of,  484 

rigor,  504 

sarcolemma,  478 

sensibility  of,  489 

serum,  485 

shape,  changes  in,  50 1 

sound  developed  in    contraction    of, 

501 
source  of  action  of,  512 
stimuli,  489 
striated,  478 
structure,  478  et  $eq. 
tetanus,  498 
unstriped,  476 
voluntary,  478 
actions  of,  507 

blood-vessels  and  nerves  of,  483 
work  of,  499 
Muscular  action,  503 
conditions  of,  502 
force,  499 
source,  £12 
Muscular  irritability,  503 

duration  of,  after  death,  504 


Nl'.KVKs. 

Muscular  motion,  476 

sense,  6« 
■  1  rebeQum  the  organ  of, 

tone.  582 
Huscnlaris  mucosa?,  293,  298,  316 
Musculi  papillaree,  135 
Musculocutaneous  plate,  780 
M  uaioal  sounds,  688 
Myograph,  495 

pendulum,  495 
Myopia,  or  short-sight,  708 
Myosin,  485 


N. 


Nabothi  glanduhv,  742 
Nails,  421 

growth  of,  421 

structure  of,  421 
Xaphthilaminc,  330 
Nasal  cavities  in  relation  to  smell,  668 

et  sea. 
Native  albumins,  845 
Natural  organic  compounds,  844 

classification  of,  iff. 
Nerve-centre,    548.      See    Cerebellum, 
Cerebrum,  Arc. 

ano-spinal,  581 

automatic  action,  563 

cardio-inhibitory,  157,  589 

cilio-spinal,  587 

conduction  in,  558 

deglutition,  296,  589 

diabetic,  £90 

diffusion  in,  559 

functions  of,  558 

genito-urinary,  581 

mastication,  279,  589 

radiation  in,  559 

reflexion  in,  ib. 

laws  and  conditions  of,  560 

respiratory,  2^0,  588 

secretion  of  saliva,  286,  5S9 

transference  of  impressions,  558 

vaso-motor,  191,  589 

vesico-spinal,  581 
Nerve-corpuscles, 

caudate  or  stellate,  549 

polar,  550 
Nerves,  540 

accelerator,  158 

action  of  stimuli  on,  514 
currents  of,  513 

afferent,  554 

axis-cylinder  of,  542 

centrifugal,  554 

centripetal,  5^4 

cerebro-spinal,  540 

classification,  542,  554 

3    L   2 


884 


INDEX. 


Nerves. 

Nerves,  continued. 
conduction  by,  553  et  seq. 

rate  of,  554 
continuity,  545 
course  of.  545 

cranial,  619.     See  Cerebral  Nerves, 
depressor,  192 
efferent,  554 

electrical  currents  of,  513 
functions  of,  552 

effect  of  chemical  stimuli  on,  514 
of  mechanical  irritation,  514 
of  temperature,  514 
funiculi  of,  541 
grey,  544 
impressions  on,  referred  to  periphery 

•  ?$?■ 

inhibitory,     554.        See     Inhibitory 

Action, 
intercentral,  554 
laws  of  conduction,  555 

of  motor  nerves,  557 

of  sensory  nerves,  555 
medullary  sheath.  542 
medullated,  542 
motor,  554 

laws  of  action  in,  5:57 
natural  currents,  513 
neurilemma,  541 
nodes  of  Ranvier,  543 
non-medullated,  544 
nuclei,  542 
of  special  sense,  557 
plexuses  of,  546 
primitive  nerve  sheath,  542 
sensory,  554 

laws  of  action  in,  555 
size  of,  544 
spinal,   569,    572,   636    et  seq.      See 

Spinal  Nerves, 
stimuli,  ^  1  \ 
structure,  541 

svmpathetie,  540,  636.     See  Sympa- 
thetic Nerve, 
terminations  of,  549 

central,  550 

in  cells,  549 

in  end-bulbs,  548 

in  motorial  end-plates,  549  ' 

in  networks  or  plexuses,  549 

m  Pacinian  corpuscles,  547 

in  touch-corpuscles,  548 
trophic,  625,  645 

u'.nar,  effect  of  compression  of,  555 
varieties  of,  541 
vaso-constrictor,  [94 
vaso-dilator,  ib. 
vaso-inhibitory,  ib. 
vaso-motor,  ib. 
white,  514 
Nervi  nervorum,  556 
Nervi  vasorum,  164 
Nervous  force,  velocity  of,  554 


Nymphs. 

Nervous  system,  540 
cerebro-spinal,  540 
development,  798 
elementary  structure  of,  540 
influence  of 

on  animal  heat,  391 

on  arteries,  192  et  seq. 

on  contractility,  488 

on   contraction  of   blood-vessels, 

190 
on  erection,  211 
on  gastric  digestion,  312 
on  the  heart's  action,  154 
on  movements  of  intestines,  359 

of  stomach,  312 
on  nutrition,  645 
on  respiration,  249 
on  secretion,  285 
on  sphincter  ani,  357 
sympathetic,  636 
Network,  intracellular,  1 1 

nuclear,  13 
Neurilemma,  541 
Neurin,  849 
Neuroglia,  41 
Nipple,  an  erectile  organ,  210 

structure  of,  406 
Nitrogen, 
in  blood,  118 

influence  of  in  decomposition,  844 
in  relation  to  food,  263  et  seq. 
in  respiration,  241 
Nitrogenous  compounds,  264 

non-nitrogenous  compounds,  264 
Nitrogenous  equilibrium,  538 
Nitrogenous  food,  265 
in  relation  to  muscular  work,  456  et 

seq. 
in  relation  to  urea,  ib. 
to  uric  acid,  458 
Nodes  of  Ranvier,  343 
Noises  in  ears,  557 

Non-azotized  or  Non -nitrogenous  food 
264 
organic  principles,  852 
Nose,  666.     See  Smell. 

irritation  referred  to,  559 
Notochord,  764 
Nucleus,  11 
position,  12 
staining  of,  12 
Nutrition,  533 
general  nature, 

of  nervous  system,  641 
of  trophic  nerves,  645 
in  paralysed  parts,  644 
of  cells,  10 
Nympba?,  742 


INDEX. 


885 


Ocri.AR  C 


0. 


Ocular  cleft,  804 

'spectrum,  72;  1 1  my, 
Odontob] 

Odo: 

causes  of,  H    , 
different  kinds  of,  O70 
perception  of,  ib. 

varies  in  different  classes,  ih, 
ttion  to  taste,  005 
phagus,  292 
Oil,  absorption  of,  375 
Oleaginous  principles,  digestion  of,  331 

Olfactory  cells,  668 

nerve,  667 
subjective  sensations  of,  671 
Olivary  body,  584 

fasciculus,  584 
Omphalo-mesenteric, 

arteries.  791 

duct,  77.S 

reins,  791 
Oncograph,  452 
Oncometer,  to. 
Ophthalmic  ganglion,  relation  of  third 

nerve,  620 
Ophthalmoscope,  716 
Optic, 

lobes,    corpora   quadrigemina   homo- 
logies of,  592 
functions  of,  593 

nerve,  decussation  of,  732 
point  of  entrance  insensible  to  light, 

713 

thalamus,  function  of,  594 

vesicle,  primary,  802 
secondary,  803 
Optical  angle,  720 

apparatus  of  eye,  699 
Ora  serrata  of  retina,  695 
Orang, 

brain  of,  608 
Organ  of  Corti,  676 
Organic  compounds  in  body,  843 

instability  of,  844 
Organs,  plurality  of  cerebral,  611 
Organs  of  sense,  development  of,  802 
Osmosis,  378 
Os  orbiculare,  673 
Os  uteri,  742 
Osseous  labyrinth,  674 
Ossicles  of  tin-  ear,  G73 

office  of,  682 
1 1— icula  auditus,  673 
Ossification,  57  k  ieq* 
Osteoblasts,  58 
Osteoclasts,  63 
Otoconia  or  Otoliths,  678 

use  of,  685 
Ovaries,  737 


Pak 
Ovaries,  route  l 

enlargement  of,  at  puberty,  741 
GraatMii  resii  lei  in,  738 
758 

Ovum,  739 

action  of  seminal  fluid  on,  758 
<  hanges  of,  in  ovary,  740 

previous  to  formation  of  embryo, 

758 

subsequent  to  cleavage,  761  • 
in  uterus,  ~yj  et  aeq. 
cleaving  of  yelk,  758 
connexion  of  with  uterus,  737 
discharge  of  from  ovary,  743 
formation  of,  740 
germinal  membrane  of,  760 
germinal  vesicle  and  spot  of,  740 
impregnation  of,  758 
structure  of,  739 
unimpregnated,  739 

Oviduct,  or  Fallopian  tube,  741 

Oxalic  acid,  449 

Oxalic  acid  in  urine,  449 

Oxygen,  843 
in  blood,  no 

consumed  in.breathing,  241 
effects  of  on  colour  of  blood,  108 
proportion  of  to   carbonic    acid,  238 
et  seq. 

Oxyhemoglobin,  112 
spectrum,  114 


Pacinian  bodies  or  corpuscles,  547 
Palate  and  uvula  in  relation  to  voice, 

529' 

cleft,  783 

Palmitin,  85; 

Pancreas,  328 

development  of,  808 
functions  of,  328 
structure,  328 
Pancreatic  fluid,  329 
Pancreatin,  854 
Papilla  foliata,  664 
Papillae 

of  the  kidney,  428 

of  skin,  distribution  of,  413 

end-bulbs  in,  416 
epithelium  of,  414 
nerve-fibres  in,  415 
supply  of  blood  to,  414 
touch  corpuscles  in,  415 
of  teeth, 
of  tongue,  661  et  aeq. 

anvallate  or  ealyciform. 
■  oiiical  or  filiform,  (JC2 
fungiform,  ib. 
Paraglobulin,  86  et  aeq. 
Paralbumin,  845 


8S6 


INDEX. 


Par  Vagum. 

Par    vagum,  631.     See    Pneumogastric 

nerve. 
Paralysed  parts, 

nutrition  of,  644 
pain  in,  556 

limbs,  temperature  of,  391 

preservation  of  sensibility  in,  576 
Paralysis,  cross,  576 
Parapeptone,  306 
Paraplegia, 

delivery  in,  581 

reflex  movements  in,  ib. 

state  of  intestines  in,  360 
Parotid  gland,  saliva  from,  279,  289 

nerves  influencing  secretion  by,  289 
Pause  in  heart's  action,  144 

respiratory,  233 
Pecten  of  birds,  804 
Peduncles, 

of  the  cerebellum,  598 

of  the  cerebrum,   or  Crura   Cerebri, 

590 
Pelvis  of  the  kidney,  428 
Penis, 

corpus  cavernosum  of,  210 

development  of,  818 

erection  of,  explained,  210 

reflex  action  in,  581 
Pepsin,  301 
Pepsinogen,  301 
Peptic  cells,  299 
Peptones,  305  it  seq. 
Perceptions  of   sensations  by   cerebral 

hemispheres.  609 
Pericardium.  127 
Perichondrium,  59 

Perilvmph,  or  fluid  of  labyrinth  of  ear, 
674 

use  of,  685 
Perimysium,  478 
Perineurium,  541 
Periosteum,  52 
Peristaltic     movements    of    intestines, 

359      , 

of  stomach,  308 
Perivascular  lymphatic  sheaths,  172 
Permanent  teeth,  76.     See  Teeth. 
Perspiration,  cutaneous,  424 

insensible  and  sensible,  424 

ordinary  constituents  of,  424 
Teyer's  glands,  318 

patches.  31S 

resemblance  to  vascular  glands,  461 

structure  of,  318 
Pfliiger's  law,  517 
Phakoscope,  704 
Pharynx.  291 

action  of  in  swallowing,  295 

influence  of  glosso-pharyngeal  nerve 
on,  296 
of  pneumogastric  nerve  on,  296 
Phenol,  857 
Phosphates,  859 


Pregnancy. 

Phosphates  in  tissues,  859 
Phosphorus  in  the  human  body,  ib. 
Pia  mater,  circulation  in,  208 
Pigment,  24 
of  hair,  418 
of  retina,  697 
of  skin,  412 
Pigment  cells,  forms  of,  24 

movements  of  granules  in,  24 
Pineal  gland,  472 
Pinna  of  ear,  672 
Pituitary  body,  472 
development,  781 
Placenta,  773  et  seq. 

fetal  and  maternal,  ib. 
Plants, 

distinctions    from    animals,  3.      See 
also  Vegetables. 
Plasma  of  blood,  80 

salts  of,  105 
Plasmine,  84 
composition,  85 
nature  of,  84 
Plethy  sinograph,  191 
Pleura,  221 
Plexus,  terminal,  549 
of  spinal  nerves,  relation  to  cord,  546 
myentericus,  315 
Auerbach's,  315 
Meissner's,  316 
Pneumogastric  nerve,  631 
distribution  of,  ib. 
influence  on 

action  of  heart,  156 
deglutition,  295 
gastric  digestion,  312 
larynx,  296 
lungs,  250 
oesophagus,  633 
pharynx,  633 
respiration,  250 
secretion  of  gastric  fluid,  312 
sensation  of  hunger,  270 
stomach,  312 
mixed  function  of,  631 
origin  from  medulla  oblongata,  586 
Poisoned  wounds,  absorption  from,  381 
Pons  Varolii,  its  structure,  590 

functions,  ib. 
Portal. 

blood,  characters  of,  108 
canals,  336 
circulation,  334 

function  of  spleen  with  regard  to. 

465 
veins,  arrangement  of,  336  et  seq. 
Portio  dura,  of  seventh  nerve,  628 

mollis,  of  seventh  nerve,  678 
Post  mortem  digestion,  313 
Potassium,  859 

sulphocyanate,  283 
Pregnancy,    absence    of    menstruation 
during,  747 


INDKX. 


887 


Prbok  ik<  r. 

I  tancj ,  miitm 
corpus  luteum  of, 
influence  on  blood, 
Presbyopia,  or  long-tight,  71- 
Primitive  groove,  762 
Primitive  nerve-sheath,  or  Schwann* 
sheath,  : 

Propionic  scid, 
ncephalon, 

land,  750 

Proteids.  ,05 
chemical  properties,  845  ei  teq. 
physical  properties,  ib. 
teste  for,  845 
varieties  of,  ib. 
Proteolytic  ferments,  307 
Protoplasm,  6 
chemical  characters,  ib. 
movement,  ib. 
nutrition,  10 
physical  char 

physiological  characters,  ib. 
reproduction,  13 
transformation  of,  17 
Proto-vertebrse,  7O4 
Psendoa    pe,  735 
Ptyalin,  283 

>n  of,  285 
Puberty, 
changes  at  period  of,  746 
indicated  by  menstruation ,  ib. 
Pulmonary  artery,  valves  of,  136 
capillaries,  166 
circulation,  226 
Pulse,  arterial.  1 77 
cause  of,  ib. 
dicrotous,  182 
difference  of  time  in  different  parts, 

frequency  of,  151 

intiuence'of  age  on,  ib. 
of  food,  posture,  etc,  152 

relation  01  to  respiration,  152 

sphvgmographic  tracings,  180  et  eeq. 

sanations,  181  et  seq. 

in  capillaries,  198 
Purkinje's  figures,  714 
Pylorus,  structure  of,  299 

"act ion  of,  309 
Pyramidal  portion  of  kidney,  428 
Pyramids  of  medulla  oblongata,  584 


ft. 


Quadrupeds,  retina-  of,  732 
Quantity  of  air  breathed,  234 
blood,  - 

saliva,  283 


BasratATOBi   Mot*w 

u. 

n 
Radiation  of  in.;  559 

Rectum,  325 
Recum  bility,  573 

559 
acquired,  y>2 
augmentation, 

-itication,  56 1 
compound,  : 

condition  y  U>,  560 

in  disease,  580 
examples  of,  563 

excito-motor  and  sensori-motor,  5U) 
inhibition  of,  563,  578 
irregular  in  disease,  580  _ 

after  separation  of  cord  from  brain, 

577  , 
laws  of,  460 
morbid,  580 
of  medulla  oblongata,  587  et  teq. 

of  spinal  cord,  577 
purposive  in  health,  560 
relation  between  a  stimulus  and,  56] 
secondary,  562 
simple,  562 
Refracting  media  of  eye,  700 
Re  fraction,  laws  of.  ib. 
Regions  of  body.     See  Frontispie 
Registering  apparatus, 
cardiograph,  [48 
kymograph,  186 
sphygmograph,  178 
Relations  between  secretions,  404 
Reptiles, 

blood-corpuscles,  95 
brain,  606 
Reserve  air,  234 
Residual  air,  234 
Respiration,  214 
abdominal  type,  231 
changes  of  air,  240 

of  blood,  244 
costal  type,  23 1 
force,  230 
frequency,  ib. 

influence*  of  nervous  system,  249 
mechanism,  228  et  seq. 
movements,    228.       See    Respiratory 

Movements, 
nitrogen  in  relation  to,  241 

oic  matter  excreted,  242 
quantitv  of  air  changed,  235 
relation  to  the  pulse,  152    - 
suspension  and  arrest,  258 
types  of,  231 
Respiratory  capacity  of  chest 
cells,  224 

functions  of  skin,  426 
movements,  228 

axes  of  rotation,  228  tt 
of  air  tubes,  218 


S8S 


INDEX. 


Eespiratory  Movements. 

Respiratory  movements,  continued. 
of  glottis,  234 

influence   on   amount    of   carbonic 
acid,  239 
on  arterial  tension,  263 
rate,  236 
relation  to  pulse  rate,  236 
size  of  animal,  ib. 
relation  to  will,  249 
various  mechanism,  245 
muscles,  228  et  seq. 
daily  work,  235 
power  of,  237 
nerve-centre,  249 
rhythm,  233 
sounds,  233 
Eestiforni  bodies,  585 
Eete  mucosum,  412 

testis,  751 
Eetiforni  or  adenoid,  or  lvmphoid  tissue. 

40 
Eetina,  694 
blind  spot,  713 
blood-vessels,  699 
duration  of  impressions  on,  714 

of  after-sensations,  715 
effect  of  pressure  on,  730 
excitation  of,  713 
focal  distance  of,  703 
fovea  centralis,  695,  713 
functions  of,  713 

image    on,    how    formed     distinctly, 
^699 
inversion  of,  how  corrected,  717 
insensible  at  entrance  of  optic  nerve, 

layers,  695 

in  quadrupeds,  732 

reciprocal  action  of  parts  of,  726 

in  relation  to  direction  of  vision,  721 
to  motion  of  bodies,  722 
to  single  vision,  729 
to  size  of  field  of  vision,  719 

reflection  of  light  from,  716 

structure  of,  694 

vessels.  699 

visual  purple,  716 
Eheoscopic  frog,  515 
Ehinence-phalon,  801 
Eibs,  axis  of  rotation,  228  et  seq. 
Eigor  mortis,  504 

affects  all  classes  of  muscles,  ib. 

phenomena  and  causes  of,  505 
Eima  glottidis,  movements  of  in  respira- 
tion, 234 
Bitter's  tetanus,  318 
Eods  of  Corti,  677 

use  of,  687 
Eouleaux,  formation  of  in  blood,  94 
Ruminants, 

stomach  of,  296 
Elimination,  ib. 
Eunning,  mechanism  of,  511 


Semen. 


Eut  or  heat,  743 


S. 


Saccharine  principles  of  food,  digestion 

of,  352 

Sacculus,  678 
Saliva,  282 

composition,  283 

process  of  secretion,  285 

quantity,  283 

rate  of  secretion,  ib. 

uses,  284 
Salivary  glands,  279 

development  of,  808 

influence  of  nervous  system,  285 

mixed,  283 

nerves,  282 

secretion,  282 

structure,  279 

true,  281 

varieties,  280 
Sarcode,  6.     See  Protoplasm. 
Sarcolemma,  478 
Sarcosin,  849 
Sarcous  elements,  479 
Scala  media,  676 

tympani,  ib. 

vestibuli,  ib. 
Sclerotic,  692 

blood-vessels,  699 
Scurvy  from  want  cf  vegetables,  268 
Sebaceous  glands,  417 

their  secretion,  423 
Sebacic  acid,  857 
Secreting  glands,  398 

aggregated,  399 

convoluted  tubular,  ib. 

tubular  or  simple,  ib. 
Secreting  membranes,  394.     See  Mucous 

and  Serous  membranes. 
Secretion,  393 

apparatus  necessary  for,  393  et  seq. 

changes  in  gland-cells  during,  402 
„         „  pancreas,  329 
,,         „  stomach,  301 
„         ,,  salivary  glands,  289 

circumstances  influencing,  403 

discharge  of,  402 

general  nature  of,  393 

influence  of  nervous  system,  404   ■ 

process  of  physical  and  chemical,  401, 
402 

serous,  395 

synovial,  396 
Segmentation  of  cells,  757 

ovum,  757 
Semen,  756 

composition  of,  ib. 

emission  of,  a  reflex  act,  581 

filaments  or  spermatozoa,  752 
purpose  of,  756 

tubes,  752 


INDEX. 


889 


Semk  iuhlak. 

Semicircular  mud*  of  car,  675 

development  of,  805  et  §$q. 
of,  685 
Semilunar  \alves,  136 

functions  of,  141 
Semilunei  of  Heidenhain,  28] 

colour,  723 

common,  646 

conditions  necessary  to,  648 

excited  by  mind,  648 

by  internal  causes,  ib. 
of  motion,  650 
nerves  of,  619  et  sea. 

impressions  on  referred  to  periphery, 

.    553,      • 

laws  ol  action,  553 

objeetive,  648 

of  pain.  ^51 

of  pressure,  655 

special,  647 

nerves  of,  619 
stimuli  of,  557 

of  special  ,557 
subjective,  557,  658.     See  also  Special 

Senses,  648. 
tactile,  651 
temperature,  656 
tickling,  652 
touch,  651 
transference  and  radiation  of,  558  et 

of  weight,  65; 
Sense,  special,  646 

of  hearing,  671.    See  Hearing,  Sound. 

of  sight,  691.     Set  Vi-ion. 

of  smell,  666.     See  Smell. 

of  taste,  658.     See  Taste. 

of  touch,  65 1 .     See  Touch. 

muscular,  655 

organs  of,  development  of,  802 
Sensory     impressions,    conduction    of. 

by  spinal  cord,  573 
nerves,  554 
Septum  between  auricles,  formation  of, 
789 
between     ventricles,     formation     of, 
ib. 
Serous  fluid ,  395 
Serous  membranes,  394 
arrangement  of,  ib. 
communication  of   lymphatics   with, 

366 
epithelium,  394 
fluid  secreted  by.  395 
functions,  ib. 
lining  joints,  etc.,  ib. 
visceral  cavities,  ib. 
stomata,  366 
structure  of,  394 
Serum, 
of  blood,  115 


SOBBXVG. 

Serum,  contbvml. 

separation  of,  8l,   1 15 

Seventh  cerebral  nerve,  auditorv  portion, 

678 

facia]  portion,  628 
Sex,  influence  on  blood,  108 

influence   on   production  of  carbonic 

acid,  239 
relation  of  to  respiratory  movements, 

Sexual    organs   and   functions    in    the 
female,  736 

in  the  male,  750 
Sexual  passion,  connection  of  with  cere- 
bellum, 599 
Sighing,  mechanism  of,  246 
Sight,  691.     Set  Vision. 
Silica,  parts  in  which  found,  859 
Silicon,  i'j. 

Singing,  mechanism  of,  248,  526  et  seq. 
Single  vision,  conditions  of,  729 
Sinus  pocularis,  817 

urogenitalis,  ib. 
Sinuses  of  dura  mater,  208 
Sixth  cerebral  nerve,  627 
Size  of  field  of  vision,  719 
Skeleton.     See  Frontispiece. 
Skin,  410 

absorption  by,  426 
of  metallic  substances,  ib. 
of  water,  ib. 

cutis  vera  of,  413 

epidermis  of,  411 

evaporation  from,  387 

excretion  by,  424 

exhalation  of  carbonic  acid  from,  424 
of  watery  vapour  from,  424 

functions  of,  422 
respiratory,  425 

papillae  of,  413 

perspiration  of,  424 

rete  mucosum  of,  412 

sebaceous  glands  of,  417 

structure  of,  410 

sudoriparous  glands  of,  416 
Sleep,  617 
Smell,  sense  of,  666 

conditions  of,  ib. 

delicacy,  669 

different  kinds  of  odours,  670 

impaired  by  lesion  of  facial  nerve,  629 

impaired  by  lesion  of  fifth  nervi  .    2 

internal  excitants  of,  671 

limited  to  olfactory  region,  667 

relation  to  common  sensibility,  669 

structure  of  organ  of,  667 

subjective  sensations,  671 

varies  in  different  animals,  670 
Sneezing,  caused  by  sun's  light,  559 

mechanism  of,  248 
Snitfing,  mechanism  of,  248 

smell,  aided  by,  667 
Sobbing,  248 


890 


IXDEX. 


Sodium. 

Sodium,  859 ^ 

in  human  body,  ib. 
salts  of  in  blood,  106 
Solitary  glands,  319 
Soluble  ferments,  852 
Somatopleure,  765 
Somnambulism,  563 

Sonorous  vibrations,  how  communicated 
in  ear,  679  et  seq. 
in  ah-  and  in  water,  ib.     See  Sound. 
Soprano  voice,  526 
Sound, 

binaural  sensations,  690 

conduction  of  by  ear,  679 

by  external  ear,  679 

by  internal  ear,  685 

by  middle  ear,  680 

movements  and  sensations  produced 

by,  691 
perception, 

of  direction  of,  688 
of  distance  of,  689 
permanence  of  sensation  of,  689 
produced  by   contraction   of  muscle, 

501 

production  of,  688 

subjective,  690 
Source  of  water,  858 
Spasms,  reflex  acts,  580 
Speaking,  ^30 

mechanism  of,  248,  530 
Special  senses,  647 
Spectrum-analysis  of  blood,  1 14 
Spectrum  or  ocular  after-sensation,  725 
Speech,  530 

function  of  tongue  in,  533 

influence  of  medulla  oblongata  on,  589 
Spermatozoa,  development  of,  752 

form  and  structure  of,  753 

function  of,  756 


motion  of,  7;6 


■10 


Spherical  aberration, 

correction  of,  ib. 
Spheroidal  epithelium,  27 
Sphincter  ani,  325,  357 

external,  357 

internal,  325 

influence  of  spinal  cord  on,  357 
Sphygmograph,  178 

tracings,  180  et  seq. 
Spinal  accessory  nerve,  635 
Spinal  cord,  565 

automatism,  583 

canal  of,  566 

centres  in,  580 

a  collection  of  nervous  centres,  5 

columns  of,  566 

commissures  of,  ib. 

conduction    of    impressions  by, 
et  seq. 

course  of  fibres  in,  571 

decussation  of  sensory  impressions  in, 
575 


573 


Stercori>". 

Spinal  cord,  continued. 

effect  of  injuries  of,  on  conduction  of 
impressions,  575  et  seq. 
on  nutrition,  645 
fissures  and  furrows  of,  566 
functions  of,  574 
of  columns,  575 
influence  on  lymph-hearts,  581 
on  sphincter  ani,  ib. 
on  tone,  582 
morbid  irritability  of,  580 
nerves  of,  569 
reflex  action  of,  577 
in  disease,  580 
inhibition  of,  578 
size  of  different  parts,  567 
special  centres  in,  580 
structure  of,  565  et  seq. 
transference,  577 
weight,  607 

relative,  ib. 
white  matter,  567 
grey  matter,  568 
Spinal  nerves,  569,  636 
origin  of,  569 
physiology  of,  572 
Spiral  canal  of  cochlea,  67 1 
lamina  of  cochlea,  ib. 
function  of,  682 
Spirometer,  235 
Splanchnic  nerve,  192,  312 
Splanchnopleure,  765 
Spleen,  461 
functions,  464 
hilus  of,  461 

influence  of  nervous  system,  466 
Malpighian  corpuscles  of,  464 
pulp,  463 
stroma  of,  ib. 
structure  of,  ib. 
trabecular  of,  ib. 
Splenic  vein,  blood  of,  109 
Spot,  germinal,  740 
Squamous  epithelium,  23 
Stammering,  533 
Stapedius  muscle,  674 

function  of,  685 
Stapes,  673 
Starch,  285 
digestion  of 
in  small  intestine,  331,  354 
in  mouth,  285 
in  stomach,  307,  354 
Starvation,  270 
appearances  after  death,  272 
efl'ect  on  temperature,  271 
loss  of  weight  in,  ib. 
period  of  death  in,  ib. 
symptoms,  ib. 
Steapsin,  331 
Stearic  acid,  856 
Stearin,  855 
Stercorin,  345 


IXDKX. 


8<JI 


Stercorin. 

Stercorin,  continued. 

allied  to  cholesterin,  345 
Stereoscope,  722 

St.  Martin.  Alexis,  .  303 

Btomaoh,  296 
blood-vessels,  302 
development,  806,  i  /  seq. 
digestion  in,  303 
circumstances  favouring,  307 
products  of,  30b 
digestion  after  death)  313 
glands,  299 
lymphatics,  302 
movements,  308 

influence  of  nervous  system,  312 
mucous  membrane,  298 
muscular  coat,  298 
nerves,  307 
ruminant,  296 

secretion  of,  303.     See  Gastric  fluid, 
structure,  297 
temperature,  303 
Stomata,  200,  366 

Stratum  intermedium  (Hannover),  74 
Striated  muscle,  478 
Stromiihr,  204 

Structural  basis  of  human  body,  5 
Stumps,  sensations  in,  556 
Succinic  arid,  857 
Succus  entericus  351 

functions  of,  352 
Sucking,  mechanism  of,  248 
Sudoriferous  glands,  41') 
their  distribution,  417 
number  of,  ib, 
their  secretion,  424 
Suffocation,  257,  <  t  seq. 
Sugar,  856 
as  food,  experiments  with,  272 
digestion  of,  352,  354 
formation  of  111  liver,  348,  350 
Sulphates,  859 
in  tissues,  859 
in  urine,  447 
Sulphuretted  hydrogen,  857 
Suprarenal  capsules,  469 
development  of.  814 
disease   of,   relation   to  discoloration 
of  skin.  471 
Structure.  469 

Sun,  a  source  of  energy,  824 
Uowiug,  294 
nerves  engaged,  295 
Sweat,  424 

Svmpathetic  nervous  system,  030 
'character    of    movements    executed 

through,  641 
conduction  of  impressions  by,  640 
diagrammatic  view,  638 
distribution.  636 
divisions  of,  540 

fibres,    differences   of    from    cerebro- 
spinal fibres,  544 


TkMI'EKATVHK. 

Sympathetic  nervous  system,  continued. 
mixture  with  oereDro-epinfl]  6 

637 
(unctions,  640 
ganglia  of,  040 

action  of,  640  et  uq. 
co-ordination  of  movements  by,  642 
structure,  '137 
in  substance  of  organs,  '42 
influence  on 

animal  heat,  391 
blood-vessels,  190  et  eeq, 
heart,  158 
intestines,  359 

involuntary  motion,  640  et  seq. 
salivary  glands,  285  et  acq. 
secretion,  ib. 
stomach,  312 
structure  of,  637 
Synovial  fluid,  secretion  of,  396 

membranes,  396 
Svntonin,  306,  846 

Systemic  circulation,   124.     See   Circu- 
lation, 
vessels,  lb. 
Systole  of  heart,  147 


T. 


Taste,  658 

after-tastes,  666 
conditions  for  perception  of,  658 
connection  with  smell,  665 
impaired  by  injury 
of  facial  nerve,  629 
of  filth  nerve,  626 
nerves  of,  626,  630 
seat  of,  658 

subjective  sensations,  666 
varieties,  665 
Taste-goblets,  664 
Taurin,  849 
Taurocholic  acid,  339 
Teeth,  67 

development,  71 
eruption,  times  of,  77 
structure  of,  68  et  seq. 
temporary  and  permanent,  75  et  seq. 
Temperament,  influence  on  blood,  108 
Temperature,  382 
average  of  body,  ib. 
changes  of,  effects  of,  383  et  seq. 
circumstances  modifying,  386 
of     cold-blooded    and    warm-blooded 

animals.  384 
in  disease,  ib. 
influence  on  amount  of  carbonic  acid 

produced,  240 
loss  of,  387 
maintenance  of,  386 
of  Mammalia,  Birds,  etc.,  384 


892 


INDEX. 


Temperature. 

Temperature,  continued. 

of  paralysed  parts,  391 

regulation  of,  386 

of  respired  air,  242 

sensation  of  variation  of,   656.     See 
Heat. 
Tendons,  structure  of,  38 

cells  of,  ib. 
Tenor  voice,  526 
Tension,  arterial,  185 
Tension  of  gases  in  lungs,  243 
Tensor  tympani  muscle,  674 

office  of,  684 
Tesselated  epithelium,  22 
Testicle,  750 

development,  813 

descent  of,  815 

structure  of,  750  et  seq. 
Tetanus,  498 
Thalamencephalon,  801 
Thalami  optici,  function  of,  594 
Thermogenic  nerves  and  nerve-centres, 

391 
Thirst,  270 

allayed  by  cutaneous  absorption,  426 
Thoracic  duct,  361 

contents,  375 
Thymus  gland,  466 

function  of,  468 

structure,  467 
Thyro-arytenoid  muscles,  527 
Thyroid  cartilage,  structure  and  connec- 
tions of,  520 
Thyroid-gland,  468 

function  of,  469 

structure,  468 
Timbre  of  voice,  526 
Tissue,  adipose,  42 

areolar,  cellular,  or  connective,  37 

elastic,  38 

fatty,  42 

fibrous,  38 

gelatinous,  39 

retiform,  40 
Tissues, 

connective,  33 

elementary  structure  of,  2,3,  et  s'eg. 

erectile,  210 
Tone  of  blood-vessels,  190 

of  muscles,  582 

of  voice,  526 
Tongue,  659 

action  of  in  deglutition,  294 
in  sucking,  248 

action  of  in  speech,  533 

epithelium  of,  663- 

influence  of  facial  nerve  on  muscles  of, 
629 

motor  nerve  of,  635 

an  organ  of  touch,  664 

papillae  of,  661 

parts  most  sensitive  to  taste,  665 

structure  of,  659 


Tyrosin. 

Tonsils,  291 

Tooth,  67.     See  Teeth. 

Tooth-ache,  radiation  of,  sensation  in, 

55? 
Tooth-pulp,  68 

Touch,  651 

after  sensation,  658 

conditions  for  perfection  of,  652 

connection  of   with  muscular  sense, 

655  . 
co-operation  of  mind  with,  658 
function  of  cuticle   with  regard  to, 

410 
of  papillae  of  skin  with  regard  to, 

410 
hand  an  organ  of,  652 
illusions,  655 
modifications  of,  651 
a  modification  of  common  sensation, 

651 
special  organs,  652 
subjective  sensations,  658 
the  tongue  an  organ  of,  653 
various  degrees  of  in  different  parts, 

653 
Touch-corpuscles,  416 

Trabecular  cranii,  781 

Trachea,  218 

Tradescantia  Yirginica,  movements  in 

cells  of,  8 
Tragus,  672 

Transference  of  impressions,  558 
Traube-Hering's  curves,  258 
Tricuspid  valve,  135 

safety-valve  action  of,  139 
Trigeminal  or  fifth  nerve,  622 

effects  of  injury  of,  623 
Trophic  nerves,  625 
Trypsin,  331 
Tripsinogen,  329 
Tube,  Eustachian,  673 
Tubercle  of  Lower,  129 
Tubes,   Fallopian,  741.     See  Fallopian 
Tubes. 

looped,  of  Henle,  431 
Tubular  glands,  399 

convoluted,  ib. 

simple,  ib. 

of  intestines,  317,  325 

of  stomach,  299 
Tubules,  21 
Tubuli  seminiferi,  752 

uriniferi,  429  et  seq. 
Tunica  albuginea  of  testicle,  750 
Tympanum  or  middle  ear,  673 

development  of,  805 

functions  of,  680 

membrane  of,  673 

structure  of,  ib. 

use  of  air  in,  682 
Types  of  respiration,  231 
Tyrosin,  330 


INDEX. 


893 


Ulceration. 


U. 


I'll  ration  of  parts  attending  injnriei 

of  nerves,  (144 
Ulnar  nerve, 

effeota  of  compression  of,  553 
Umbilical  arteries,  778 

contraction  of,  177 

cord,  778 

reside,  760.  767 
Unconscious  1  erebration,  611 
Unorganised  ferments,  852 
Unstnped  muscular  fibre,  476 

development,  483 

distribution,  476 

structure,  477 
Urachus,  771 
Urate  of  amnionium,  444 

of  sodium,  444 
Urea,  441 

apparatus    for    estimating    quantity, 

,443, 

chemical  composition  of,  442, 

identical  with  cyanate  of  ammonium, 
%b. 

properties,  441 

quantity,  443 

in  relation  to  muscular  exertion,  457 

sources,  450 
Ureides,  851 
Ureter,  436 

Urethra,  development  of,  818 
Uric  acid,  444 

condition  in  which  it  exists  in  urine, 

444 
forms  in  which  it  is  deposited,  443 

proportionate  quantity  of,  444 

source  of,  458 

tests,  445 

variations  in  quantity,  444 
Urina  sanguinis,  potus,  et  cibi,  440 
Urinary  bladder.  430 

development,  815 

nerves,  431 

regurgitation  from  prevented,  459 

structure,  430 
Urinary  ferments,  438,  855 
Urine,  437 

abnormal,  441 

analysis  of,  437 

chemical  composition,  ib. 

colouring  matter  of,  446 

cyst  in  in,  44c) 

decomposition  by  mucus,  438 

effect  of  blood-pressure  on,  453 

expulsion,  460 

extractives,  447 

rlow  of  into  bladder,  459 

gases,  450 

hippuric  acid  in,  446 

mucus  in,  446 

oxalic  acid  in,  449 


Vaso-constuictoii  Nehvi  .-. 

Urine,  continued. 
physical  characters,  1  ^7 
pigments,  j  )'> 

quantity  of  chief  constituents,  139 
reaction  of,  438 
in  different  animals,  438 

made  alkaline  by  diet,  43*) 
saline  matter,  447 
secretion,  455 
effects  or  posture,  etc.,  on,  45') 
rate  of,  ib. 
solids,  441 

variations  of,  439 
specific  gravity  oi,  440 

variations  of,  440 
urates,  444,  445 
urea,  441 
uric  acid  in,  444 

variations  of  specific  gravity,  440 
of  water,  439 
Urobilin,  446 
Urochrome,  446 
Uroerythrin,  446 
Uses  of  blood,  113 
Uterus,  741 

change  of  mucous  membrane  of,  745 
development  of  in  pregnancy,  745 
follicular  glands  of,  742 
masculinus,  817 
reflex  action  of,  581 
structure,  741 
Utriculus  of  labyrinth,  678 
Uvula  in  relation  to  voice,  529 


Vagina,  structure  of,  742 

Vagus  nerve,  286.      See  Pneurnogastric. 

Valerianic  acid,  856 

Valve,  ileo-csecal,  structure  of,  326 

of  Vieussens,  595 
Valves  of  heart,  135 

action  of,  139,  et  seq. 

bicuspid  or  mitral,  135 

semilunar,  136,  141 

tricuspid,  135,  136 

of  lymphatic  vessels,  368 

of  veins,  170  et  st  q, 
Valvula*  conniventes,  317 
Vas  deferens,  751 

development,  813 
Vasa  erf'erentia  of  testicle,  751 
of  kidney,  434 

recta  of  kidney,  435 
of  testicle,  751 

vasorum,  162 
Vascular  area,  768 
Vascular  -lands,  46T 

in  relation  to  blood,  472 

several  offices  of,  472 
Vascular  system,  development  of,  785 
Vaso-constrictor  nerves,  194 


894 


INDEX. 


Yaso-dilator  Nerves. 

Vaso-dilator  nerves,  194 

Yaso-motor  influence  on  blood-pressure, 

192  et  seq. 
Yaso-motor  nerves,  191 
effect  of  section,  191  et  seq. 
influence  upon  blood-pressure,  192 
Yaso-motor  nerve-centres,  191 

reflection  by,  191 
Vegetables    and    animals,    distinctions 

between,  3 
Yeins,  168 
anastomoses  of.  201 
blood-pressure  in,  202 
circulation  in,  201  et  seq. 

rate  of,  206 
cardinal,  793 

collateral  circulation  in,  201 
cranium,  208 
development,  793 
distribution,  168 
effects  of  muscular  pressure  on.  202 

of  respiration  on,  254 
force  of  heart's  action  remaining  in, 

201 
influence  of  expiration,  255 

inspiration,  253 
influence  of  gravitation  in,  203 
parietal  system  of,  793  et  seq. 
pressure  in.  202 
rhythmical  action  in,  202 
structure  of,  168 
systemic,  126 
umbilical,  778 
valves  of,  170 
velocity  of  blood  in,  206 
visceral  system  of,  793  et  seq. 
Yelocity  of  blood  in  arteries,  204 
in  capillaries,  206 
in  veins,  206 
of  circulation,  203 
of  nervous  force,  554 
Yena  porta?,  109,  334 
Yen*  hepatica?  advehentes,  794 

revehentes.  ib. 
Yentilation.  252 
Yentricles  of  heart,  138 
capacity  of,  132 
contraction  of,  138 

effect  on  blood-current    iu   veins, 

„    153 

dilatation  of,  ib. 

force  of,  ib. 

of  larynx,  office  of,  530 
Yentriloquism,  532,  689 
Vermicular     movement    of    intestines, 

_       .359 

\  ermiform  process,  325 
Vertebrae,  development  of,  778 
Vesicle,  germinal,  740 

Graafian,  738 
bursting  of,  743 

umbilical,  760.  767 
Yesicula  germinativa,  740 


Yocal  Cords. 

Yesicula;  seminales,  754 
functions  of,  754 
reflex  movements  of,  581 
structure,  754 
Vestibule  of  the  ear,  674 
Vestigial  fold  of  Marshall,  796 
Yibrations,    conveyance  of  to  auditory 
nerve,  679  et  seq. 
perception  of,  688 
of  vocal  cords,  52c 
Yidian  nerve,  628 
Villi  in  chorion,  772 

in  placenta,  776 
Villi  of  intestines,  321 

action  in  digestion,  322 
Visceral  arches,  development  of,  782 
connection  with  cranial  nerves,  783 
lamina?  or  plates,  767 
Vision,  691 
angle  of,  720 
at   different  distances,   adaptation  of 

eye  to,  703  et  seq. 
contrasted  with  touch,  72  r 
corpora   quadrigemina,  the  principal 

nerve-centres  of,  592 
correction  of  aberration,  710  et  seq. 

of  inversion  of  image,  7 1 7 
defects  of,  708  et  seq. 
distinctness     of,     how    secured,    699 

et  seq, 
double,  730 

duration  of  sensation  in.  714 
estimation  of  the  form  of  objects,  721 
of  their  direction,  721 
of  their  motion,  722 
of  their  size,  720 
field  of,  size  of,  719 
focal  distance  of,  703 
impaired  by  lesion    of   fifth    nerve, 

624 
influence  of  attention  on,  723 
modified    by    different  parts  of   the 

retina.  726 
purple,  716 
in  quadrupeds,  732 
single,  with  two  eyes,  732 
Visual  direction.  721* 
Vital  or  respiratorv  capacity  of  chest, 

235 
\  ital  capillary  force,  200 
Vital  force.  837 
Yitellin.  846 
Vitelline  duct,  767 

membrane,  739 

spheres,  759 
Vitreous  humour,  701 
Yocal  cords,  521 

action  of  in  respiratory  actions.  234 
et  seq. 

approximation  of,  effect  on  height  of 
note,  523 

elastic  tissue  in,  39 

longer  in  males  than  in  females.  1.26 


INDEX. 


895 


V(w  \i.  COBDS. 

\  itthturtl. 

position  of,  hon  modified,  525 
vibrations  of,  cam  ;2o 

\ 
of  b 

conditions  on  v/hieh  strength  depends, 

,  .  5*7 
\        .  human,  produced  by  vibration  of 

il  1  orus,  518,  523 

in  eunuchs,  527 
influence  <>f  age  on, 

of  arches  of  palate  ami  uvula,  529 

of  epiglottis,  524 

of  sex,  526 
influence  of  ventricles  of  larynx,  530 

of  vocal  cords,  ^25 
in  male  and  female.  526 

cause  of  different  pitch,  526 
modulations  of,  526 
natural  and  falsetto,  528 
peculiar  characters  of,  526 
varieties  of,  527 
Vomiting1,  310 

action  of  stomach  in,  ib. 
nerve-actions  in,  312 
voluntary  and  acquired,  311 
Vowels  and*  consonants,  530 
Vulvo-vaginal    or    Duvernev's    glands, 

743 


W. 

Walking,  509 

Water,  858 
absorbed  by  skin,   426 

by  stomach,  353 
amount, 
in  blood,  variations  in,  102,  107 
exhaled  from  lungs,  241 
from  skin,  425 
forms  large  part  of  human  body,  858 
influence  of  on  coagulation  of  blood, 
89 


ZOX  \     I'i  I  I.t'f  IDA. 

Water,  1  ontinued. 
influence  of  on  decomposition,  N44 
in  urine,  excretion  of,  450 

variations  in.  }  n 
loss  of  from  body,  858 

nses,  ib. 
quantity  in  rations  tissues,  ib. 
source,  ib. 

ii-  of  in  atmosphere,  238 

Wave  of  bl l  causing  the  pulse,  177 

velocity  of,  178 
White  corpuscles,  98.     See  Blood-cor- 
puscles, white  :    and   Lymph-cor- 
puscles. 
White  fibro-cartilage,  49 

fibrous  tissue,  38 
Willis,  circle  of,  208 
Wolffian  bodies,  810  et  xetj. 
Work  of  heart,  153 


Xanthin,  447 
Xantho-proteic  reaction,  845 


Yawning,  248 

Yelk,  or  vitellus,  757 

changes  of,  in  Fallopian  tube,  758 

cleaving  of,  ib. 

constriction  of,   by   ventral    lamina*, 

1  elk-sac,  767  et  uq. 
Yellow  elastic  fibre,  36,  39 

fibro-cartilage.  4.9 

spot  of  Summering,  698 
Young-Helmholtz  theory,  724 


Zimmermann,  corpuscles  of,  467 
Zona  pellucida,  739 


THE    END. 


CATALOGUE  No.  7. 


A  CATALOGUE 


OF 


BOOKS  FOR  STUDENTS; 

INCLUDING   A    FULL    LIST   OF 

The  fQuiz-  Com  paid s  ? 

AND    MANY   OF 

THE   MOST   PROMINENT 

Students'  Manuals  and  Text-Books 


FUBLISHED    BY 


P.  BLAKISTOX,  SOX  &  CO.. 

Medical  Booksellers,  Importers  and  Publishers, 
No.  1012  WALNUT  STREET, 

PHILADELPHIA. 


***  For  sale  by  all  Booksellers,  or  any  book  will  be  sent  by  mail, 
postpaid,  upon  receipt  of  price.  Catalogues  of  books  on  all  branches 
o<  Medicine,  Dentistry,  Pharmacy,  etc.,  supplied  upon  application. 


THE  PQUIZ-COMPENDS? 

A  NEW  SERIES  OF  COMPENDS  FOR  STUDENTS. 

For  Use  in  the  Quiz  Class  and  when 
Preparing  for  Examinations. 

Price  of  Each,  Bound  in  Cloth,  $1.00    Interleaved,  $1.25. 


Based  on  the  most  popular  text- books,  and  on  the  lec- 
tures of  prominent  professors,  they  form  a  most  complete 
set  of  manuals,  containing  information  nowhere  else 
collected  in  such  a  condensed,  practical  shape.  The 
authors  have  had  large  experience  as  quiz  masters  and 
attaches  of  colleges,  with  exceptional  opportunities  for 
noting  the  most  recent  advances  and  methods.  The 
arrangement  of  the  subjects,  illustrations,  types,  etc.,  are 
all  of  the  most  improved  form,  and  the  size  of  the  books 
is  such  that  they  may  be  easily  carried  in  the  pocket. 

No.  1.    ANATOMY.     (Illustrated.) 

THIRD  REVISED  EDITION. 
A  Compend  of  Human  Anatomy.     By  Samuel  O.  L. 
Potter,  m.a.,  m.d.,  U.  S.  Army.  With  63  Illustrations. 

"  The  work  is  reliable  and  complete,  and  just  what  the  student 
needs  in  reviewing  the  subject  for  his  examinations." — The  Physi- 
cian and  Surgeon's  Investigator,  Buffalo,  N.  Y. 

"To  those  desiring  to  post  themselves  hurriedly  for  examination, 
this  little  book  will  be  useful  in  refreshing  the  memory." — New 
Orleans  Medical  and  Surgical  Journal. 

"The  arrangement  is  well  calculated  to  facilitate  accurate  memo- 
rizing, and  the  illustrations  are  clear  and  good." — North  Carolina 
Medical  Journal. 

Nos.  2  and  3.     PRACTICE. 
A  Compend  of    the   Practice  of    Medicine,  especially 

adapted  to  the  use  of  Students.  By  Dan'l  E.  Hughes. 

M.D.,  Demonstrator  of  Clinical  Medicine  in  Jefferson 

Medical  College,  Philadelphia.     In  two  parts. 

Part  I. — Continued,  Eruptive,  and  Periodical  Fevers. 
Diseases  of  the  Stomach,  Intestines,  Peritoneum,  Biliary 
Passages,  Liver,  Kidneys,  etc.,  and  General  Diseases,  etc. 

Part  II. — Diseases  of  the  Respirator)'  System,  Circu- 
latory System,  and  Nervous  System ;  Diseases  of  the 
Blood,  etc. 

***  These  little  books  can  be  regarded  as  a  full  set  of 
notes  upon  the   Practice   of    Medicine,   containing   the 


THE  ?  QUIZ-COMPENDS  ?. 


Synonyms.  Definitions,  Causes,  Symptoms,  Prognosis. 
Diagnosis,  Treatment,  etc.,  of  each  disease,  and  includ- 
ing a  number  of  new  prescriptions.  They  have  been 
compiled  from  the  lectures  of  prominent  Professors,  and 
reference  has  been  made  to  the  latest  writings  of  Pro- 
fessors Flint,  DaCosta,  REYNOLDS,  Bartholow, 
ROBERTS  and  others. 

"  It  is  brief  and  concise,  and  at  the  same  time  possesses  an  accu- 
racy not  generally  found  in  compends." — fas.  M.  French,  M.D., 
Ass't  to  the  Prof,  of  Practice,  Medical  College  of  Ohio,  Cincinnati. 

"  The  book  seems  very  concise,  yet  very  comprehensive.     . 
An  unusually  superior  book." — Dr.  E.  T.  Bruen,  Demonstrator 
inical  Medicine,  l/ni?>ersily  of  Pennsylvania. 

"  I  have  used  it  considerably  in  connection  with  my  branches  in 
the  Quiz-class  of  the  University  of  La." — J.  H.  Bemiss,  AVn 
Orleans. 

"  Dr.  Hughes  has  prepared  a  very  useful  little  book,  and  I  shall 
take  pleasure  in  advising  my  class  to  use  it." — Dr.  George  W 
Hall,  Prof essor  of  Practice ,  St.  Louis  College  of  Physicians  ami 
Surgeons. 

No.  4.     PHYSIOLOGY. 
A  Compend  of  Human  Physiology,  adapted  to  the  use 

of  Students.     By  Albert    P.  Brubaker,  m.d.,  De 

monstrator  of  Physiology  in  Jefferson  Medical  College. 

Philadelphia. 

"  Dr.  Brubaker  deserves  the  hearty  thanks  of  medical  students 
for  his  Compend  of  Physiology.  He  has  arranged  the  fundamental 
and  practical  principles  of  the  science  in  a  peculiarly  inviting  and 
accessible  manner.  I  have  already  introduced  the  work  to  my 
class." — Maurice  X.  Miller,  M.D.,  Instructor  in  Practical  His- 
tology,  formerly  Demonstrator  of  Physiology,  University  City  oj 
New  York. 

"  '  Quiz-Compend '  No.  4  is  fully  up  to  the  high  standard  estab- 
lished by  its  predecessors  of  the  same  series." — Medical  Bulletin, 
Philadelphia. 

"  I  can  recommend  it  as  a  valuable  aid  to  the  student." — C.  A". 
Ellinwood,  M.D.,  Professor  of  Physiology,  Cooper  Medical  Col- 
lege, San  Francisco. 

"  This  is  a  well  written  little  book." — London  Lancet. 

No.  5.     OBSTETRICS. 
A  Compend  of  Obstetrics.   For  Physicians  and  Students. 

By  Henry  G.  LANDIS,  m.d.,  Professor  of  Obstetrics 

and  Diseases  of  Women,  in  Starling  Medical  College, 

Columbus.     Illustrated. 

"  We  have  no  doubt  that  many  students  will  find  in  it  a  most  val- 
uable aid  in  preparing  for  examination." — The  American  fourna. 
of  Obstetrics . 

"  It  is  complete,  accurate  and  scientific.  The  very  best  book  o; 
its  kind  I  have  seen." — f.  S.  Knox,  M.D.,  Lecturer  on  Obstetrics 
Rush  Medical  College,  Chicago. 

Price  of  each  Book,  Cloth.  $1.00.    Interleaved  for  Notes,  $1.25. 


THE  ?  QUIZ-COMPENDS  ?. 


"  I  have  been  teaching  in  this  department  for  many  years,  and  am 
free  to  say  that  this  will  be  the  best  assistant  I  ever  had.  It  is  ac- 
curate and  comprehensive,  but  brief  and  pointed." — Prof.  P.  D. 
Yost,  St.  Louis. 

No.  6.     MATERIA  MEDICA.     Revised  Ed. 

A  Compend  on  Materia  Medica  and  Therapeutics,  with 
especial  reference  to  the  Physiological  Actions  of 
Drugs.  For  the  use  of  Medical,  Dental,  and  Pharma- 
ceutical Students  and  Practitioners.  Based  on  the  New 
Revision  I  Sixth)  of  the  U.  S.  Pharmacopoeia,  and  in- 
cluding many  unofficinal  remedies.  By  Samuel  O. 
L.  Potter,.  m.a.,m.d.,  U.  S.  Army. 

"  I  have  examined  the  little  volume  carefully,  and  find  it  just 
such  a  book  as  I  require  in  my  private  Quiz,  and  shall  certain!}'  re- 
commend it  to  my  classes.  Your  Compends  are  all  popular  here  in 
Washington." — John  E.  Brackett,  M.D.,  Professor  of  Materia 
Medica  and  Therapeutics ,  Hcnuard  Medical  College,  Washington. 

"  Part  of  a  series  of  small  but  valuable  text-books.  .  .  .  While 
the  work  is,  owing  to  its  therapeutic  contents,  more  useful  to  the 
medical  student,  the  pharmaceutical  student  may  derive  much  use- 
ful information  from  it." — N.  Y.  Pharmaceutical  Record. 

No.  7.     CHEMISTRY.    Revised  Ed. 

A  Compend  of  Chemistry.     By  G.  Mason*  Ward,  m.d., 
Demonstrator  of  Chemistry  in  Jefferson  Medical  Col- 
lege, Philadelphia.    Including  Table  of  Elements  and 
various  Analytical  Tables. 
"  Brief,  but  excellent.  ...  It  will  doubtless  prove  an  admirable 

aid  to  the  student,  by  fixing  these  facts  in  his  memory.    It  is  worthy 

the  study  of  both  medical  and  pharmaceutical   students   in  this 

branch." — Pharmaceutical  Record,  New  York. 

No.  8.    VISCERAL  ANATOMY. 
A  Compend  of  Visceral  Anatomy.     By  Samuel  O.  L. 
Potter,  m.a..  m.d.,  U.  S.  Army.    With  40  Illustrations. 

***  This  is  the  only  Compend  that  contains  full  descriptions  of  the 
viscera,  and  will,  together  with  No.  i  of  this  series,  form  the  only 
complete  Compend  of  Anatomy  published. 

No.  9.  STJRG-ERY.  Illustrated. 
A  Compend  of  Surgery;  including  Fractures,  Wounds, 
Dislocations,  Sprains,  Amputations  and  other  opera- 
tions, Inflammation,  Suppuration,  Ulcers,  Syphilis, 
Tumors,  Shock,  etc.  Diseases  of  the  Spine,  Ear,  Eye, 
Bladder,  Testicles,  Anus,  and  other  Surgical  Diseases. 
By  Orville  Horwitz,  a.m.,  m.d.,  with  43  Illustra- 
tions. 
Price  of  Each,  Cloth,  $1.00.    interleaved  for  Notes,  $1.25. 


THE  TQUIZ-COMPENDS?. 


No.  10.     ORGANIC  CHEMISTRY. 

JUST  PUBLISHED. 
•  ompend  of  Organic  Chemistry,  including  Medical 
Chemistry,  Urine  Analysis,  and  the  Analysis  of  V 
and  Food,  etc.  By  Hknry  LeFFMANN,  m.d.,  Pro 
fessor  of  Clinical  Chemistry  and  Hygiene  in  the  Phila- 
delphia Polyclinic ;  Professor  of  Chemistry,  Penn- 
sylvania College  of  Dental  Surgery;  Member  of  the 
V.  Medico-Legal  Society.  Cloth.     $1.00. 

Interleaved,  for  the  addition  of  Notes,  $1.25. 

Nature  of  Organic  Bodies.  Transformations  under  various  con- 
ditions. Organic  Synthesis.  Homologous  and  Isomeric  Bodies. 
Empirical  and  Rational  formulae.  Classification  of  Organic  Bodies. 
Hydrocarbon.  Derivatives  of  Hydrocarbons,  Alcohols  and  Ethers. 
Benzenes  and  Turpenes.  Fat  Acids,  Oils  and  Fats,  Sugars,  Glyco- 
sides. Cyanogen  Compounds  Amines  and  Amides.  Alkaloids. 
Ptomaines.  Animal  Chemistry.  Nutrition  and  Assimilation. 
Food,  Water  and  Air.     Urinary  Analysis.     Index. 

The  Essentials  of  Pathology. 

BY  D.  TOD  GILLIAM,  M.D., 

Professor  of  Physiology  in  Starling  Medical  College,  Columbus ,0 
With  47  Illustrations.  12mo.  Cloth.  Price  $2.00. 
***  The  object  of  this  book  is  to  unfold  to  the  beginner  the  funda- 
mentals of  pathology  in  a  plain,  practical  way,  and  by  bringing  them 
within  easy  comprehension  to  increase  his  interest  in  the  study  of 
the  subject.  Though  it  will  not  altogether  supplant  larger  works, 
it  will  be  found  to  impart  clear-cut  conceptions  of  the  generally 
accepted  doctrines  of  the  day,  and  to  prevent  confusion  in  the  mind 
of  the  student. 

A  POCKET-BOOK  OF 

PHYSICAL    DIAGNOSIS 

OF   THE 

Diseases  of  the  Heart  and  Lungs. 

A   MANUAL   FOR   STUDENTS  AND   PHYSICIANS. 

BY  DR.  EDWARD  T.  BRUEN, 
ononstrator  of  Clinical  Medicine  in  the  University  of  Pennsyl- 
vania, Assistant  Physician  to  the  University  Hospital,  etc. 

Second  Edition.  Revised.    With  new  Illustrations.    12mo.    $1.50. 

%*The  subject  is  treated  in  a  plain,  practical  manner,  avoiding 
questions  of  historical  or  theoretical  interest,  and  without  h 
special  claim  to  originality  of  matter,  the  author  has  made  a  book 
that  presents  the  somewhat  difficult  points  of  Physical  Diagnosis 
clearly  and  distinctly. 


STUDENTS'  MANUALS. 


TYSON,  ON  THE  URINE.  A  Practical  Guide  to 
the  Examination  of  Urine.  For  Physicians  and  Stu- 
dents. By  James  Tyson,  m.d.,  Professor  of  Path- 
ology and  Morbid  Anatomy,  University  of  Pennsylva- 
nia. With  Colored  Plates  and  Wood  Engravings. 
Fourth  Edition.  i2mo,  cloth,  $1.50 

HEATH'S  MINOR  SURGERY.  A  Manual  of 
Minor  Surgery  and  Bandaging.  By  Christopher 
Heath,  m.d.,  Surgeon  to  University  College  Hospital, 
London.     6th  Edition.     115  111.      i2mo,  cloth,  $2.00 

MACNAMARA,  ON  THE  EYE.  A  Manual  for 
Students  and  Physicians.  4  Colored  Plates  and  65 
Wood  Engravings.     Demi  8vo.  Cloth,  $4.00. 

VIRCHOW'S  POST-MORTEMS.  Post-Mortem 
Examinations.  A  Description  and  Explanation  of  the 
Methods  of  Performing  them.  By  Prof.  Rudolph 
Virchow,  of  Berlin.  Translated  by  Dr.  T.  B.  Smith. 
2d  Ed.     4  Lithographic  Plates.         i2mo,  cloth,  #1.25 

DULLES'  ACCIDENTS  AND  EMERGEN- 
CIES. What  To  Do  First  in  Accidents  and  Emer- 
gencies. A  Manual  Explaining  the  Treatment  of 
Surgical  and  other  Accidents,  Poisoning,  etc.  By 
Charles  W.  Dulles,  m.d.,  Surgeon  Out-door  De- 
partment, Presbyterian  Hospital,  Philadelphia.  Col- 
ored Plate  and  other  Illustrations.        32mo,  cloth,  .75 

BEALE,  ON  SLIGHT  AILMENTS.  Their  Na- 
ture and  Treatment.  By  Lionel  S.  Beale,  m.d., 
F.R.s.  Second  Edition.  Revised,  Enlarged  and  Illus- 
trated.    283  pages.     8vo. 

Paper  covers,  75  cents;  cloth,  $1.25 

ALLINGHAM,  ON  THE  RECTUM.  Fistulse, 
Hemorrhoids,  Painful  Ulcer,  Stricture,  Prolapsus,  and 
other  Diseases  of  the  Rectum ;  Their  Diagnosis  and 
Treatment.  By  Wm.  Allingham,  m.d.  Fourth  Re- 
vised and  Enlarged  Edition.     Illustrated.     8vo. 

Paper  covers,  75  cents;  cloth,  $1.25 

AITKEN,  THE  SCIENCE  AND  PRACTICE 
OF  MEDICINE.  A  New  (Seventh)  Edition.  2 
Vols.     8vo.  Cloth,  Si 2.00;  Leather,  $14.00. 


STUDENTS'  MANUALS  AND  1!  XI 


MARSHALL  AND  SMITH,  ON  THE  URINE. 
The  Chemical  Analysis  of  the  Urine.  By  [OHN  Mak- 
bh  \i  i ,  M.D.,  Chemical  Laboratory,  University  of  Penn< 
gylvania,  and  Prof.  E.  F.  Smith.  [11ns.  Cloth,  $i  oo 

MEARS*     PRACTICAL    SURGERY.       Surgical 

indaging,  Ligation,  Amputation,  etc.     By 

J.  BwiNG  Meak>.  m.d.,   Demonstrator  of  Surgery  in 

Jefferson  Med.  College.  227  Illus.    2d  Ed.     In  Press. 

KIRKE'S  PHYSIOLOGY.  A  Handbook  for  Stu- 
dents. Eleventh  Edition,  1884.  466  Illustrations. 
I  >emi  8vo.  Cloth,  #5.00. 

TYSON,  ON  THE  CELL  DOCTRINE;  its  His- 
tory and  Present  State.  By  Prof.  JAMES  Tyson,  m.D. 
Second  Edition.     Illustrated.  i2mo,  cloth,  $2.00 

MEADOWS'  MIDWIFERY.  A  Manual  for  Stu- 
dents. By  Alfred  Meadows,  m.d.  From  Fourth 
London  Edition.     145  Illustrations.    8vo,  cloth,  S2.00 

WYTHE'S  DOSE  AND  SYMPTOM  BOOK. 
Containing  the  Doses  and  Uses  of  all  the  principal 
Articles  of  the  Materia  Medica,  etc.  Eleventh  Edi- 
tion.        32mo,  cloth,  $1.00;  pocket-book  style,  $1.25 

PHYSICIAN'S  PRESCRIPTION  BOOK.  Con- 
taining Lists  of  Terms,  Phrases,  Contractions  and 
Abbreviations  used  in  Prescriptions,  Explanatory  Notes, 
Grammatical  Construction  of  Prescriptions,  etc.,  etc. 
By  Prof.  Jonathan  Pereira,  m.d.  Sixteenth  Edi- 
tion.        32mo,  cloth,  $1.00;  pocket-book  style,  $1.25 

POCKET  LEXICONS. 

CLEAVELAND'S  POCKET  MEDICAL  LEXI- 
CON. A  Medical  Lexicon,  containing  correct  Pro- 
nunciation and  Definition  of  Terms  used  in  Medi- 
cine and  the  Collateral  Sciences.  Thirtieth  Edition. 
Very  small  pocket  size.     Red  Edges. 

Cloth,  75  cents;  pocket-book  style,  #1.00 

LONGLEY'S    POCKET    DICTIONARY.      The 

Student's  Medical  Lexicon,  giving  TJefinition  and  Pro- 
nunciation of  all  Terms  used  in  Medicine,  with  an 
Appendix  giving  Poisons  and  Their  Antidotes,  Abbre- 
viations used  in  Prescriptions,  Metric  Scale  of  Doses, 
etc.  241110,  cloth,  $1.00;  pocket-book  style,  $  1.25 


ROBERTS'  PRACTICE. 

Fifth  Edition. 
Recommended  as  a    Text-book  at   University  of  Pennsylvania, 

Long  Island  College  Hospital,  Yale  and  Harvard  Colleges, 

Bishop's  College,  Montreal,  University  of  Michigan,  and 

over  twenty  other  Medical  Schools. 

A  HANDBOOK  OF  THE  THEORY  AND   PRACTICE  OF 

MEDICINE.     By  Frederick  T.   Roberts,  m.d.,  m.r.c.p., 

Professor  of  Clinical  Medicine  and  Therapeutics  in  University 

College  Hospital,  London.     Fifth  Edition.     Octavo. 

CLOTH,  $5.00;  LEATHER,  $6.00. 

*#*  This  new  edition  has  been  subjected  to  a  careful  revision. 
Many  chapters  have  been  rewritten.  Important  additions  have  been 
made  throughout,  and  new  illustrations  introduced. 

"A  clear,  yet  concise,  scientific  and  practical  work.  It  is  a  capi- 
tal compendium  of  the  classified  knowledge  of  the  subject." — Prof. 
J.  Adams  Allen,  Rush  Medical  College,  Chicago. 

"  I  have  become  thoroughly  convinced  of  its  great  value,  and 
have  cordially  recommended  it  to  my  class  in  Yale  College."— 
Prof.  David  P.  Smith. 

"  I  have  examined  it  with  some  care,  and  think  it  a  good  book, 
and  shall  take  pleasure  in  mentioning  it  among  the  works  which 
may  properly  be  put  in  the  hands  of  students." — A.  B.  Palmer, 
Prof,  of  the  Practice  of  Medicine,   University  of  Michigan. 

"  It  is  unsurpassed  by  any  work  that  has  fallen  into  our  hands, 
as  a  compendium  for  students  preparing  for  examination.  It  is 
thoroughly  practical,  and  fully  up  to  the  times." — The  Clinic. 

By  Same  Author. 

ROBERTS'  NOTES  ONMATERIA  MEDICA 

AND    PHARMACY. 

Just  Ready,     nmo.    Cloth.  Price  $2.00. 

A  new  Compend  for  Students. 


BIDDLE'S  MATERIA  MEDICA. 

Ninth  Revised  Edition. 

Recommended  as  a    Text-book  at    Yale    College,    University  of 

Michigan,   College  of  Physicians  and  Surgeons,  Baltimore , 

Baltimore  Medical  College,  Louisville  Medical  College, 

and  a  number  of  other  Colleges  throughout  the  U.  S. 

BIDDLE'S  MATERIA  MEDICA.  For  the  Use  of  Students  and 
Physicians.  By  the  late  Prof.  John  B.  Biddle,  m.d.,  Profes- 
sor of  Materia  Medica  in  Jefferson  Medical  College,  Philadelphia. 
The  Ninth  Edition,  thoroughly  revised,  and  in  many  parts  re- 
written, by  his  son,  Clement  Biddle,  m.d.,  Past  Assistant 
Surgeon,  U.  S.  Navy,  assisted  by  Henry  Morris,  m.d. 

CLOTH,  $4.00  ;  LEATHER,  $4.75. 
"  I  shall   unhesitatingly  recommend  it  (the  9th  Edition)  to  my 

students  at  the  Bellevue  Hospital  Medical  College. — Prof. 

A.  A.  Smith,  New  York,  fune,  1883. 
"  The  larger  works  usually  recommended  as  text-books  in  our 

medical  schools  are  too  voluminous  for  convenient  use.     This  work 

will  be  found  to  contain  in  a  condensed  form  all  that  is  most  valuable, 

and  will  supply  students  with  a  reliable  guide." — Chicago  Med.  Jl 
***  This  Ninth  Edition  contains  all  the  additions  and  changes  in 

the  U.  S.  Pharmacopoeia,  Sixth  Revision. 


STANDARD  TEXT-BOOKS. 


BLOXAM'S  CHEMISTRY.  Inorganic  and  Organic,  with  Ex- 
periment..    Fifth  Edition,     Revisedand  [Uusti 

8vo,  cloth,  $3.75 ;  leather,  £4. 75 

CARPENTER  ON  THE  MICROSCOPE  and  lis  Revelations. 
Sixth  Edition,  Enlarged.  With  500  Illustrations  and  Colored 
Plates,  handsomely  printed.  Demi  8vo,  cloth,  $5.50 

FLOWER,  DIAGRAMS  OF  THE  NERVES  of  the  Human 
<  >ti^in.  I  >i  visions,  Connections,  etc.  410,  cloth,  $3.50 

GLISAN'S  MODERN  MIDWIFERY.  A  Text-hook.  129 
Illustrations.  8vo,  cloth,  $4.00;  leather,  $5.00 

HOLDEN'S  OSTEOLOGY.  A  Description  of  the  Hones,  with 
Colored  Delineations  of  the  Attachments  of  the  Muscles.  Sixth 
Edition.     61  Lithographic  Plates  and  many  Wood   Engravings. 

Royal  8vo,  cloth,  $6.00 

HEADLAND,  THE  ACTION  OF  MEDICINE  in  the  System. 
Ninth  American  Kdition.  8vo,  cloth,  $3.00 

MANN'S  PSYCHOLOGICAL  MEDICINE  and  Allied  Ner- 
vous Diseases;  including  the  Medico- Legal  Aspects  of  Insanity. 
With  Illustrations.  8vo,  cloth,  $5.00  ;  leather,  $6. 00. 

MEIGS  AND  PEPPER  ON  CHILDREN".  A  Practical  Trea- 
tise on  Diseases  of  Children.     Seventh  Edition,  Revised. 

8vo,  cloth,  $6.00  ;  leather,  $7.00 

PARKES'  PRACTICAL  HYGIENE.  Sixth  Revised  and  En- 
larged Edition.     Illustrated.  8vo,  cloth,  $3.00 

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WILSON'S  HUMAN  ANATOMY.  General  and  Special. 
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WYTHE'S  MICROSCOPIST.  A  Manual  of  Microscopy  and 
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ACTON,  ON  THE  REPRODUCTIVE  ORGANS.  Their 
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HOLDEN'S  ANATOMY.        Fifth  Edition. 
JUST  PUBLISHED. 

A  MANUAL  OF  THE  DISSECTION 

OF  THE  HUMAN  BODY. 

By  Luther  Holden,  m.d.,  Late  President  of  the  Royal  College 
of  Surgeons  of  England,  Consulting  Surgeon  to  St.  Bartholomew's 
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REESE'S 
MEDICAL   JURISPRUDENCE 

AND  TOXICOLOGY. 

A  Text-book  of  Medical  Jurisprudence  and  Toxicology'.  By 
John  J.  Reese,  m.  d.,  Professor  of  Medical  Jurisprudence  and 
Toxicology-  in  the  Medical  and  Law  Departments  of  the  University 
of  Pennsylvania:  Vice-President  of  the  Medical  Jurisprudence  So- 
ciety of  Philadelphia  ;  Physician  to  St.  Joseph's  Hospital ;  Corres- 
ponding Member  of  the  New  York  Medico-legal  Society.  One 
Volume.    Demi  Octavo.    606  pages.    Cloth,  $4.00;  Leather,  $5.00. 

"  Professor  Reese  is  so  well  known  as  a  skilled  medical  jurist 
that  his  authorship  of  any  work  virtually  guarantees  the  thorough- 
ness and  practical  character  of  the  latter.  And  such  is  the  case  in 
the  book  before  us.  *  *  *  *  We  might  call  these  the 
essentials  for  the  study  of  medical  jurisprudence.  The  subject 
is  skeletonized,  condensed,  and  made  thoroughly  up  to  the  wants  of 
the  general  medical  practitioner,  and  the  requirements  of  prose- 
cuting and  defending  attorneys.  If  any  section  deserves  more  dis- 
tinction than  any  other,  as  to  intrinsic  excellence,  it  is  that  on  toxi- 
cology. This  part  of  the  book  comprises  the  best  oudine  of  th-; 
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the  work  is  everything  it  promises  and  more,  and  considering  its 
size,  condensation,  and  practical  character,  it  is  by  far  the  most 
useful  one  for  ready  reference  that  we  have  met  with.  It  is  well 
printed  and  neatly  bound. — Ar.  I '.  Medical  Record,  Sept.  13th, :  \ 

RICHTER'S  CHEMISTRY, 

A  TEXT-BOOK  of  INORGANIC  CHEMISTRY  for  STUDENTS 

By  PROF.  VICTOR  von  RICHTER, 

University  of  Breslau, 

Authorized  Translation  from  the  Third  German  Editi ■:  n 

By  EDGAR  F.  SMITH,  M.A.,  Ph.D., 

Professor  of  Chemistry  in  Wittenberg  College,  Spring -fi eld,  Ohio; 
formerly  in  the  Laboratories  of  the  University  of  Pennsyl- 
vania; Member  of  the  Chemical  Society  of  Berlin. 

•.2mo.  89  Wood-cuts  and  Col.  Lithographic  Plate  of  Spectra.  $2.00 

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presentation  of  the  theories  and  facts  of  the  science.  These  are 
usually  taught  apart,  as  if  entirely  independent  of  each  other,  and 
those  experienced  in  teaching  the  subject  know  only  too  well  the 
trouble  encountered  in  attempting  to  get  the  student  properly  in- 
terested in  the  science  and  in  bringing  him  to  a  clear  comprehension 
of  the  same.  In  this  work  of  Prof,  von  Richter,  which  has  beer, 
received  abroad  with  such  hearty  welcome,  two  editions  having 
been  rapidly  disposed  of,  theory  and  fact  are  brought  close  together, 
and  their  intimate  relation  clearly  shown.  From  careful  observa- 
tion of  experiments  and  their  results,  the  student  is  led  to  a  correct 
understanding  of  the  interesting  principles  of  chemistry. 

In  preparation,  "ORGANIC  CHEMISTRY,'  By  the  same 
author.     Translated. 


fust  PtMUkedy  September,  1I&4. 

VAN  HARLINGEN  ON  SKIN  DISEASES. 

A  Handbook  of   the   I  of  the  Skin,  their  Di 

and  Treatment.    By  Arthur  Van  Harlingen,  lf.D., 

"cssor  of  Diseases  of  the   Skin   in  the  Philadelphia 
clinic,  Consulting  Physician  to  the  Dispensary   for 
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12M0.    284  PAGES.     CLOTH.    PRICE  $1.75. 
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number  of  figures,  accurately  colored,  showing  the  appearance  of 
various  lesions,  and  will  be  found  to  give  great  aid  in  diagnosing. 

BYFORD,  DISEASES  OF  WOMEN. 

NEW  REVISED  EDITION. 
The  Practice  of  Medicine  and  Surgery,  as  applied  to  the 
Diseases  of  Women.  By  W.  II.  BYFORD,  a.m.,  m.d.. 
Professor  of  Gynaecology  in  Rush  Medical  College ; 
of  Obstetrics  in  the  Woman's  Medical  College ;  Sur- 
geon to  the  Woman's  Hospital;  President  of  the 
American  Gynaecological  Society,  etc.  Third  Edition. 
Revised  and  Enlarged;  much  of  it  Rewritten;  with 
over  160  Illustrations.     Octavo. 

PRICE,  CLOTH,  $5.00:  LEATHER.  S6.00. 
•'  The  treatise  is  as  complete  a  one  as  the  present  state  of  our 
science  will  admit  of  being  written.    We  commend  it  to  the  diligent 
study  of  every  practitioner  and  student,  as  a  work  calculated  to  in- 
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partment, and  has  embodied  in  the  present  work  the  results  of  a 
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of  the  most  valuable  practical  works  issued  from   the  American 
press." — Chicago  Medical  Examiner. 

MACKENZIE,  THE  THROAT  AND  NOSE. 

By  Morell  Mackenzie,  m.d.,  Senior  Physician  to  the 

Hospital  for  Diseases  of  the  Chest  and  Throat ;  Lecturer 

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YEO'S   PHYSIOLOGY. 

A  MANUAL  FOR  STUDENTS.     JUST  READY. 

300     CAREFULLY    PRINTED    ILLUSTRATIONS. 

FULL  GLOSSARY  AND  INDEX. 

By  Gerald  F.  Yeo,  m.d.,  f.r.c.s.,  Professor  of  Physi- 
ology in  King's  College,  London.  Small  Octavo.  750 
pages.     Over  300  carefully  printed  Illustrations. 

PRICE,  CLOTH.  $4.00:  LEATHER,  $5.00. 

"  By  his  excellent  manual,  Prof.  Yeo  has  supplied  a  want  which 
must  have  been  felt  by  every  teacher  of  physiology.  *  *  *  * 
In  conclusion,  we  heartily  congratulate  Prof.  Yeo  on  his  work, 
which  we  can  recommend  to  all  those  who  wish  to  find  within  a 
moderate  compass  a  reliable  and  pleasantly  written  exposition  of 
all  the  essential  facts  of  physiology  as  the  science  now  stands." — 
The  Dublin  Journal  of  Med.  Science. 

"The  work  will  take  a  high  rank  among  the  smaller  text-books 
of  Physiology." — Prof.  H.  P.  Bowditch,  Harvard  Med.  School, 
Boston. 

"  The  brief  examination  I  have  given  it  was  so  favorable  that  I 
placed  it  in  the  list  of  text-books  recommended  in  the  circular  of 
the  University  Medical  College." — Prof.  Lewis  A.  Stimpson, 
M.  D.,  37  East  33d  Street,  New  York. 

"  For  students'  use  it  is  one  of  the  very  best  text-books  in  Physi- 
ology."— Prof.  L.  B.  How,  Dartmouth  Med.  College,  Hanover, 
N.H. 

RINDFLEISCH. 

THE  ELEMENTS  OF  PATHOLOGY. 

TRANSLATED  BY  WM.  H.  MERCUR,  M.D. 
REVISED   AND   EDITED   BY  PROF.  JAS.  TYSON, 

Of  the  Uniziersity  of  Pennsylvania. 
263  PAGES.  CLOTH.  PRICE  $2.00. 
*#*  It  is  the  object  of  Prof.  Rindfleisch  to  present  in 
this  volume  of  moderate  size  the  fundamental  principles 
of  Pathology  A  large  number  of  the  general  processes 
which  underlie  disease,  a  knowledge  of  which  is  essen- 
tial to  the  practical  physician,  are  plainly  presented. 
They  include,  among  others,  inflammation,  tumor  forma- 
tion, fever,  derangements  of  nutrition,  including  atrophy, 
derangements  of  the  movement  of  the  blood,  of  blood 
formation  and  blood  purification,  hyperesthesia,  anaesthe- 
sia, convulsions,  paralysis,  etc.  The  well-known  reputa- 
tion of  the  author,  his  thorough  familiarity  with  and  his 
method  of  treating  the  subject,  make  this  most  recent  work 
peculiarly  useful  to  the  student,  as  well  as  to  the  prac- 
ticing physician  who  wishes  to  brush  up  his  pathology. 


I 


